Charles Darwin........................................................................................................................................1

CRITICAL INTRODUCTION. ...............................................................................................................1

CHAPTER I.ATOLLS OR LAGOONISLANDS. ...........................................................................8

CHAPTER II.BARRIER REEFS. ....................................................................................................24

CHAPTER III.FRINGING OR SHOREREEFS. ...........................................................................29

CHAPTER IV.ON THE DISTRIBUTION AND GROWTH OF CORALREEFS. ......................32

CORALREEFS. .................................................................................................................................45

THE THEORY OF THEIR FORMATION. ........................................................................................59

INDEX. ...............................................................................................................................................104

Although in some respects more technical in their subjects and style than Darwin's "Journal," the books here

reprinted will never lose their value and interest for the originality of the observations they contain. Many

parts of them are admirably adapted for giving an insight into problems regarding the structure and changes

of the earth's surface, and in fact they form a charming introduction to physical geology and physiography in

their application to special domains. The books themselves cannot be obtained for many times the price of the

present volume, and both the general reader, who desires to know more of Darwin's work, and the student of

geology, who naturally wishes to know how a master mind reasoned on most important geological subjects,

will be glad of the opportunity of possessing them in a convenient and cheap form.

The three introductions, which my friend Professor Judd has kindly furnished, give critical and historical

A scientific discovery is the outcome of an interesting process of evolution in the mind of its author. When

we are able to detect the germs of thought in which such a discovery has originated, and to trace the

successive stages of the reasoning by which the crude idea has developed into an epochmaking book, we

have the materials for reconstructing an important chapter of scientific history. Such a contribution to the

story of the "making of science" may be furnished in respect to Darwin's famous theory of coralreefs, and

The subject of corals and coralreefs is one concerning which much popular misconception has always

prevailed. The misleading comparison of coralrock with the combs of bees and the nests of wasps is perhaps

responsible for much of this misunderstanding; one writer has indeed described a coralreef as being "built

by fishes by means of their teeth." Scarcely less misleading, however, are the references we so frequently

meet with, both in prose and verse, to the "skill," "industry," and "perseverance" of the "coralinsect" in

"building" his "home." As well might we praise men for their cleverness in making their own skeletons, and

laud their assiduity in filling churchyards with the same. The polyps and other organisms, whose remains

accumulate to form a coralreef, simply live and perform their natural functions, and then die, leaving behind

them, in the natural course of events, the hard calcareous portions of their structures to add to the growing

While the forms of coralreefs and coralislands are sometimes very remarkable and worthy of attentive

study, there is no ground, it need scarcely be added, for the suggestion that they afford proofs of design on the

part of the living builders, or that, in the words of Flinders, they constitute breastworks, defending the

It was not till the beginning of the present century that travellers like Beechey, Chamisso, Quoy and Gaimard,

Moresby, Nelson, and others, began to collect accurate details concerning the forms and structure of

coralmasses, and to make such observations on the habits of reefforming polyps, as might serve as a basis

for safe reasoning concerning the origin of coralreefs and islands. In the second volume of Lyell's

"Principles of Geology," published in 1832, the final chapter gives an admirable summary of all that was then

known on the subject. At that time, the ringform of the atolls was almost universally regarded as a proof that

they had grown up on submerged volcanic craters; and Lyell gave his powerful support to that theory.

Charles Darwin was never tired of acknowledging his indebtedness to Lyell. In dedicating to his friend the

second edition of his "Naturalist's Voyage Round the World," Darwin writes that he does so "with grateful

pleasure, as an acknowledgment that the chief part of whatever scientific merit this journal and the other

works of the author may possess, has been derived from studying the wellknown and admirable 'Principles

The second volume of Lyell's "Principles" appeared after Darwin had left England; but it was doubtless sent

on to him without delay by his faithful friend and correspondent, Professor Henslow. It appears to have

reached Darwin at a most opportune moment, while, in fact, he was studying the striking evidences of slow

and longcontinued, but often interrupted movement on the west coast of South America. Darwin's acute

mind could not fail to detect the weakness of the then prevalent theory concerning the origin of the

ringshaped atollsand the difficulty which he found in accepting the volcanic theory, as an explanation of

In an interesting fragment of autobiography, Darwin has given us a very clear account of the way in which

the leading idea of the theory of coralreefs originated in his mind; he writes, "No other work of mine was

begun in so deductive a spirit as this, for the whole theory was thought out on the west coast of South

America, before I had seen a true coralreef. I had therefore only to verify and extend my views by a careful

examination of living reefs. But it should be observed that I had during the two previous years been

incessantly attending to the effects on the shores of South America of the intermittent elevation of the land,

together with the denudation and deposition of sediment. This necessarily led me to reflect much on the

effects of subsidence, and it was easy to replace in imagination the continued deposition of sediment by the

upward growth of corals. To do this was to form my theory of the formation of barrierreefs and atolls."

On her homeward voyage, the "Beagle" visited Tahiti, Australia, and some of the coralislands in the Indian

Ocean, and Darwin had an opportunity of testing and verifying the conclusion at which he had arrived by

I well recollect a remarkable conversation I had with Darwin, shortly after the death of Lyell. With

characteristic modesty, he told me that he never fully realised the importance of his theory of coralreefs till

he had an opportunity of discussing it with Lyell, shortly after the return of the "Beagle". Lyell, on receiving

from the lips of its author a sketch of the new theory, was so overcome with delight that he danced about and

threw himself into the wildest contortions, as was his manner when excessively pleased. He wrote shortly

afterwards to Darwin as follows:"I could think of nothing for days after your lesson on coralreefs, but of

the tops of submerged continents. It is all true, but do not flatter yourself that you will be believed till you are

growing bald like me, with hard work and vexation at the incredulity of the world." On May 24th, 1837,

Lyell wrote to Sir John Herschel as follows:"I am very full of Darwin's new theory of coralislands, and

have urged Whewell to make him read it at our next meeting. I must give up my volcanic crater forever,

though it cost me a pang at first, for it accounted for so much." Dr. Whewell was president of the Geological

Society at the time, and on May 31st, 1837, Darwin read a paper entitled "On Certain Areas of Elevation and

Subsidence in the Pacific and Indian oceans, as deduced from the Study of Coral Formations," an abstract of

It was about this time that Darwin, having settled himself in lodgings at Great Marlborough Street,

commenced the writing of his book on "CoralReefs." Many delays from illhealth and the interruption of

other work, caused the progress to be slow, and his journal speaks of "recommencing" the subject in February

1839, shortly after his marriage, and again in October of the same year. In July 1841, he states that he began

once more "after more than thirteen month's interval," and the last proofsheet of the book was not corrected

till May 6th, 1842. Darwin writes in his autobiography, "This book, though a small one, cost me twenty

months of hard work, as I had to read every work on the islands of the Pacific, and to consult many charts."

The task of elaborating and writing out his books was, with Darwin, always a very slow and laborious one;

but it is clear that in accomplishing the work now under consideration, there was a long and constant struggle

with the lethargy and weakness resulting from the sad condition of his health at that time.

Lyell's anticipation that the theory of coralreefs would be slow in meeting with general acceptance was

certainly not justified by the actual facts. On the contrary the new book was at once received with general

assent among both geologists and zoologists, and even attracted a considerable amount of attention from the

It was not long before the coralreef theory of Darwin found an able exponent and sturdy champion in the

person of the great American naturalist, Professor James D. Dana. Two years after the return of the "Beagle"

to England, the ships of the United States Exploring Expedition set sail upon their four years' cruise, under

the command of Captain Wilkes, and Dana was a member of the scientific staff. When, in 1839, the

expedition arrived at Sydney, a newspaper paragraph was found which gave the American naturalist the first

intimation of Darwin's new theory of the origin of atolls and barrierreefs. Writing in 1872, Dana describes

the effect produced on his mind by reading this passage:"The paragraph threw a flood of light over the

subject, and called forth feelings of peculiar satisfaction, and of gratefulness to Mr. Darwin, which still come

up afresh whenever the subject of coral islands is mentioned. The Gambier Islands in the Paumotus, which

gave him the key to the theory, I had not seen; but on reaching the Feejees, six months later, in 1840, I found

there similar facts on a still grander scale and of a more diversified character, so that I was afterward enabled

to speak of his theory as established with more positiveness than he himself, in his philosophic caution, had

been ready to adopt. His work on coralreefs appeared in 1842, when my report on the subject was already in

manuscript. It showed that the conclusions on other points, which we had independently reached, were for the

most part the same. The principal points of difference relate to the reason for the absence of corals from some

coasts, and the evidence therefrom as to changes of level, and the distribution of the oceanic regions of

elevation and subsidencetopics which a wide range of travel over the Pacific brought directly and

Among the Reports of the United States Exploring Expedition, two important works from the pen of

Professor Dana made their appearance;one on "Zoophytes," which treats at length on "Corals and

CoralAnimals," and the other on "CoralReefs and Islands." In 1872, Dana prepared a work of a more

popular character in which some of the chief results of his studies are described; it bore the title of "Corals

and CoralIslands." Of this work, new and enlarged editions appeared in 1874 and 1890 in America, while

two editions were published in this country in 1872 and 1875. In all these works their author, while

maintaining an independent judgment on certain matters of detail, warmly defends the views of Darwin on all

Another able exponent and illustrator of the theory of coralreefs was found in Professor J.B. Jukes, who

accompanied H.M.S. "Fly", as naturalist, during the survey of the Great BarrierReefin the years 1842 to

1846. Jukes, who was a man of great acuteness as well as independence of mind, concludes his account of the

great Australian reefs with the following words:"After seeing much of the Great BarrierReefs, and

reflecting much upon them, and trying if it were possible by any means to evade the conclusions to which Mr.

Darwin has come, I cannot help adding that his hypothesis is perfectly satisfactory to my mind, and rises

As the result of the clear exposition of the subject by Darwin, Lyell, Dana, and Jukes, the theory of

coralreefs had, by the middle of the present century, commanded the almost universal assent of both

biologists and geologists. In 1859 Baron von Richthofen brought forward new facts in its support, by

showing that the existence of the thick masses of dolomitic limestone in the Tyrol could be best accounted for

if they were regarded as of coralline origin and as being formed during a period of long continued subsidence.

The same views were maintained by Professor Mojsisovics in his "Dolomitriffe von Sudtirol und Venetien,"

The first serious note of dissent to the generally accepted theory was heard in 1863, when a distinguished

German naturalist, Dr. Karl Semper, declared that his study of the Pelew Islands showed that uninterrupted

subsidence could not have been going on in that region. Dr. Semper's objections were very carefully

considered by Mr. Darwin, and a reply to them appeared in the second and revised edition of his

"CoralReefs," which was published in 1874. With characteristic frankness and freedom from prejudice,

Darwin admitted that the facts brought forward by Dr. Semper proved that in certain specified cases,

subsidence could not have played the chief part in originating the peculiar forms of the coralislands. But

while making this admission, he firmly maintained that exceptional cases, like those described in the Pelew

Islands, were not sufficient to invalidate the theory of subsidence as applied to the widely spread atolls,

encircling reefs, and barrierreefs of the Pacific and Indian Oceans. It is worthy of note that to the end of his

life Darwin maintained a friendly correspondence with Semper concerning the points on which they were at

After the appearance of Semper's work, Dr. J.J. Rein published an account of the Bermudas, in which he

opposed the interpretation of the structure of the islands given by Nelson and other authors, and maintained

that the facts observed in them are opposed to the views of Darwin. Although, so far as I am aware, Darwin

had no opportunity of studying and considering these particular objections, it may be mentioned that two

American geologists have since carefully reexamined the districtProfessor W.N. Rice in 1884 and

Professor A. Heilprin in 1889and they have independently arrived at the conclusion that Dr. Rein's

The most serious opposition to Darwin's coralreef theory, however, was that which developed itself after the

return of H.M.S. "Challenger" from her famous voyage. Mr. John Murray, one of the staff of naturalists on

board that vessel, propounded a new theory of coralreefs, and maintained that the view that they were

formed by subsidence was one that was no longer tenable; these objections have been supported by Professor

Alexander Agassiz in the United States, and by Dr. A. Geikie, and Dr. H.B. Guppy in this country.

Although Mr. Darwin did not live to bring out a third edition of his "CoralReefs," I know from several

conversations with him that he had given the most patient and thoughtful consideration to Mr. Murray's paper

on the subject. He admitted to me that had he known, when he wrote his work, of the abundant deposition of

the remains of calcareous organisms on the sea floor, he might have regarded this cause as sufficient in a few

cases to raise the summits of submerged volcanoes or other mountains to a level at which reefforming corals

can commence to flourish. But he did not think that the admission that under certain favourable conditions,

atolls might be thus formed without subsidence, necessitated an abandonment of his theory in the case of the

A letter written by Darwin to Professor Alexander Agassiz in May 1881 shows exactly the attitude which

careful consideration of the subject led him to maintain towards the theory propounded by Mr.

Murray:"You will have seen," he writes, "Mr. Murray's views on the formation of atolls and barrierreefs.

Before publishing my book, I thought long over the same view, but only as far as ordinary marine organisms

are concerned, for at that time little was known of the multitude of minute oceanic organisms. I rejected this

view, as from the few dredgings made in the "Beagle", in the south temperate regions, I concluded that shells,

the smaller corals, etc., decayed and were dissolved when not protected by the deposition of sediment, and

sediment could not accumulate in the open ocean. Certainly, shells, etc., were in several cases completely

rotten, and crumbled into mud between my fingers; but you will know whether this is in any degree common.

I have expressly said that a bank at the proper depth would give rise to an atoll, which could not be

distinguished from one formed during subsidence. I can, however, hardly believe in the existence of as many

banks (there having been no subsidence) as there are atolls in the great oceans, within a reasonable depth, on

which minute oceanic organisms could have accumulated to the depth of many hundred feet."

Darwin's concluding words in the same letter written within a year of his death, are a striking proof of the

candour and openness of mind which he preserved so well to the end, in this as in other controversies.

"If I am wrong, the sooner I am knocked on the head and annihilated so much the better. It still seems to me a

marvellous thing that there should not have been much, and longcontinued, subsidence in the beds of the

great oceans. I wish some doubly rich millionaire would take it into his head to have borings made in some of

the Pacific and Indian atolls, and bring home cores for slicing from a depth of 500 or 600 feet."

It is noteworthy that the objections to Darwin's theory have for the most part proceeded from zoologists,

while those who have fully appreciated the geological aspect of the question, have been the staunchest

supporters of the theory of subsidence. The desirability of such boring operations in atolls has been insisted

upon by several geologists, and it may be hoped that before many years have passed away, Darwin's hopes

may be realised, either with or without the intervention of the "doubly rich millionaire."

Three years after the death of Darwin, the veteran Professor Dana reentered the lists and contributed a

powerful defence of the theory of subsidence in the form of a reply to an essay written by the ablest exponent

of the antiDarwinian views on this subject, Dr. A. Geikie. While pointing out that the Darwinian position

had been to a great extent misunderstood by its opponents, he showed that the rival theory presented even

During the last five years, the whole question of the origin of coralreefs and islands has been reopened,

and a controversy has arisen, into which, unfortunately, acrimonious elements have been very unnecessarily

introduced. Those who desire it, will find clear and impartial statements of the varied and often mutually

destructive views put forward by different authors, in three works which have made their appearance within

the last year,"The Bermuda Islands," by Professor Angelo Heilprin; "Corals and CoralIslands," new

edition by Professor J.D. Dana; and the third edition of Darwin's "CoralReefs," with Notes and Appendix by

Most readers will, I think, rise from the perusal of these works with the conviction that, while on certain

points of detail it is clear that, through the want of knowledge concerning the action of marine organisms in

the open ocean, Darwin was betrayed into some grave errors, yet the main foundations of his argument have

not been seriously impaired by the new facts observed in the deepsea researches, or by the severe criticism

to which his theory has been subjected during the last ten years. On the other hand, I think it will appear that

much misapprehension has been exhibited by some of Darwin's critics, as to what his views and arguments

really were; so that the reprint and wide circulation of the book in its original form is greatly to be desired,

and cannot but be attended with advantage to all those who will have the fairness to acquaint themselves with

The object of this volume is to describe from my own observation and the works of others, the principal kinds

of coralreefs, more especially those occurring in the open ocean, and to explain the origin of their peculiar

forms. I do not here treat of the polypifers, which construct these vast works, except so far as relates to their

distribution, and to the conditions favourable to their vigorous growth. Without any distinct intention to

classify coralreefs, most voyagers have spoken of them under the following heads: "lagoonislands," or

"atolls," "barrier" or "encircling reefs," and "fringing" or "shorereefs." The lagoonislands have received

much the most attention; and it is not surprising, for every one must be struck with astonishment, when he

first beholds one of these vast rings of coralrock, often many leagues in diameter, here and there

surmounted by a low verdant island with dazzling white shores, bathed on the outside by the foaming

breakers of the ocean, and on the inside surrounding a calm expanse of water, which from reflection, is of a

bright but pale green colour. The naturalist will feel this astonishment more deeply after having examined the

soft and almost gelatinous bodies of these apparently insignificant creatures, and when he knows that the

solid reef increases only on the outer edge, which day and night is lashed by the breakers of an ocean never at

rest. Well did Francois Pyrard de Laval, in the year 1605, exclaim, "C'est une merueille de voir chacun de ces

atollons, enuironne d'un grand banc de pierre tout autour, n'y ayant point d'artifice humain." The

accompanying sketch of Whitsunday island, in the South Pacific, taken from Captain Beechey's admirable

"Voyage," although excellent of its kind, gives but a faint idea of the singular aspect of one of these

Whitsunday Island is of small size, and the whole circle has been converted into land, which is a

comparatively rare circumstance. As the reef of a lagoonisland generally supports many separate small

islands, the word "island," applied to the whole, is often the cause of confusion; hence I have invariably used

in this volume the term "atoll," which is the name given to these circular groups of coralislets by their

Barrierreefs, when encircling small islands, have been comparatively little noticed by voyagers; but they

well deserve attention. In their structure they are little less marvellous than atolls, and they give a singular

and most picturesque character to the scenery of the islands they surround. In the accompanying sketch, taken

from the "Voyage of the 'Coquille'," the reef is seen from within, from one of the high peaks of the island of

Bolabola. (I have taken the liberty of simplifying the foreground, and leaving out a mountainous island in the

far distance.) Here, as in Whitsunday Island, the whole of that part of the reef which is visible is converted

into land. This is a circumstance of rare occurrence; more usually a snowwhite line of great breakers, with

here and there an islet crowned by cocoanut trees, separates the smooth waters of the lagoonlike channel

from the waves of the open sea. The barrierreefs of Australia and of New Caledonia, owing to their

enormous dimensions, have excited much attention: in structure and form they resemble those encircling

With respect to fringing, or shorereefs, there is little in their structure which needs explanation; and their

name expresses their comparatively small extension. They differ from barrierreefs in not lying so far from

the shore, and in not having within a broad channel of deep water. Reefs also occur around submerged banks

of sediment and of worndown rock; and others are scattered quite irregularly where the sea is very shallow;

these in most respects are allied to those of the fringing class, but they are of comparatively little interest.

I have given a separate chapter to each of the above classes, and have described some one reef or island, on

which I possessed most information, as typical; and have afterwards compared it with others of a like kind.

Although this classification is useful from being obvious, and from including most of the coralreefs existing

in the open sea, it admits of a more fundamental division into barrier and atollformed reefs on the one hand,

where there is a great apparent difficulty with respect to the foundation on which they must first have grown;

and into fringingreefs on the other, where, owing to the nature of the slope of the adjoining land, there is no

such difficulty. The two blue tints and the red colour (replaced by numbers in this edition.) on the map (Plate

III.), represent this main division, as explained in the beginning of the last chapter. In the Appendix, every

existing coralreef, except some on the coast of Brazil not included in the map, is briefly described in

geographical order, as far as I possessed information; and any particular spot may be found by consulting the

Several theories have been advanced to explain the origin of atolls or lagoonislands, but scarcely one to

account for barrierreefs. From the limited depths at which reefbuilding polypifers can flourish, taken into

consideration with certain other circumstances, we are compelled to conclude, as it will be seen, that both in

atolls and barrierreefs, the foundation on which the coral was primarily attached, has subsided; and that

during this downward movement, the reefs have grown upwards. This conclusion, it will be further seen,

explains most satisfactorily the outline and general form of atolls and barrierreefs, and likewise certain

peculiarities in their structure. The distribution, also, of the different kinds of coralreefs, and their position

with relation to the areas of recent elevation, and to the points subject to volcanic eruptions, fully accord with

this theory of their origin. (A brief account of my views on coral formations, now published in my Journal of

Researches, was read May 31st, 1837, before the Geological Society, and an abstract has appeared in the

In the several original surveys, from which the small plans on this plate have been reduced, the coralreefs

are engraved in very different styles. For the sake of uniformity, I have adopted the style used in the charts of

the Chagos Archipelago, published by the East Indian Company, from the survey by Captain Moresby and

Lieutenant Powell. The surface of the reef, which dries at low water, is represented by a surface with small

crosses: the coralislets on the reef are marked by small linear spaces, on which a few cocoanut trees, out of

all proportion too large, have been introduced for the sake of clearness. The entire ANNULAR REEF, which

when surrounding an open expanse of water, forms an "atoll," and when surrounding one or more high

islands, forms an encircling "barrierreef," has a nearly uniform structure. The reefs in some of the original

surveys are represented merely by a single line with crosses, so that their breadth is not given; I have had

such reefs engraved of the width usually attained by coralreefs. I have not thought it worth while to

introduce all those small and very numerous reefs, which occur within the lagoons of most atolls and within

the lagoonchannels of most barrierreefs, and which stand either isolated, or are attached to the shores of

the reef or land. At Peros Banhos none of the lagoonreefs rise to the surface of the water; a few of them

have been introduced, and are marked by plain dotted circles. A few of the deepest soundings are laid down

Figure 1.VANIKORO, situated in the western part of the South Pacific; taken from the survey by Captain

D'Urville in the "Astrolabe;" the soundings on the southern side of the island, namely, from thirty to forty

fathoms, are given from the voyage of the Chev. Dillon; the other soundings are laid down from the survey

by D'Urville; height of the summit of the island is 3,032 feet. The principal small detached reefs within the

lagoonchannel have in this instance been represented. The southern shore of the island is narrowly fringed

by a reef: if the engraver had carried this reef entirely round both islands, this figure would have served (by

leaving out in imagination the barrierreef) as a good specimen of an abruptlysided island, surrounded by a

Figure 2.HOGOLEU, or ROUG, in the Caroline Archipelago; taken from the "Atlas of the Voyage of the

'Astrolabe,'" compiled from the surveys of Captains Duperrey and D'Urville; the depth of the immense

Figure 3.RAIATEA, in the Society Archipelago; from the map given in the quarto edition of "Cook's First

Figure 4.BOW, or HEYOU ATOLL (or lagoonisland), in the Low Archipelago, from the survey by

Captain Beechey, R.N.; the lagoon is choked up with reefs, but the average greatest depth of about twenty

Figure 5.BOLABOLA, in the Society Archipelago, from the survey of Captain Duperrey in the "Coquille:"

the soundings in this and the following figures have been altered from French feet to English fathoms; height

Figure 6.MAURUA, in the Society Archipelago; from the survey by Captain Duperrey in the "Coquille:"

Figure 7.POUYNIPETE, or SENIAVINE, in the Caroline Archipelago; from the survey by Admiral Lutke.

Figure 8.GAMBIER ISLANDS, in the southern part of the Low Archipelago; from the survey by Captain

Beechey; height of highest island, 1,246 feet; the islands are surrounded by extensive and irregular reefs; the

Figure 9.PEROS BANHOS ATOLL (or lagoonisland), in the Chagos group in the Indian Ocean; from

the survey by Captain Moresby and Lieutenant Powell; not nearly all the small submerged reefs in the lagoon

Figure 10.KEELING, or COCOS ATOLL (or lagoonisland), in the Indian Ocean; from the survey by

Captain Fitzroy; the lagoon south of the dotted line is very shallow, and is left almost bare at low water; the

part north of the line is choked up with irregular reefs. The annular reef on the northwest side is broken, and

Coralconglomerate.Lagoon.Calcareous sediment.Scari and Holuthuriae subsisting on

corals.Changes in the condition of the reefs and islets. Probable subsidence of the atoll.Future state

A.Level of the sea at low water: where the letter A is placed, the depth is twentyfive fathoms, and the

distance rather more than one hundred and fifty yards from the edge of the reef.

B.Outer edge of that flat part of the reef, which dries at low water: the edge either consists of a convex

mound, as represented, or of rugged points, like those a little farther seaward, beneath the water.

D.A low projecting ledge of brecciated coralrock washed by the waves at high water.

E.A slope of loose fragments, reached by the sea only during gales: the upper part, which is from six to

twelve feet high, is clothed with vegetation. The surface of the islet gently slopes to the lagoon.

KEELING or COCOS atoll is situated in the Indian Ocean, in 12 deg 5' S., and longitude 90 deg 55' E.: a

reduced chart of it was made from the survey of Captain Fitzroy and the Officers of H.M.S. "Beagle," is

given in Plate I., Figure 10. The greatest width of this atoll is nine miles and a half. Its structure is in most

respects characteristic of the class to which it belongs, with the exception of the shallowness of the lagoon.

The accompanying woodcut represents a vertical section, supposed to be drawn at low water from the outer

coast across one of the low islets (one being taken of average dimensions) to within the lagoon.

The section is true to the scale in a horizontal line, but it could not be made so in a vertical one, as the

average greatest height of the land is only between six and twelve feet above highwater mark.

I will describe the section, commencing with the outer margin. I must first observe that the reefbuilding

polypifers, not being tidal animals, require to be constantly submerged or washed by the breakers. I was

assured by Mr. Liesk, a very intelligent resident on these islands, as well as by some chiefs at Tahiti

(Otaheite), that an exposure to the rays of the sun for a very short time invariably causes their destruction.

Hence it is possible only under the most favourable circumstances, afforded by an unusually low tide and

smooth water, to reach the outer margin, where the coral is alive. I succeeded only twice in gaining this part,

and found it almost entirely composed of a living Porites, which forms great irregularly rounded masses (like

those of an Astraea, but larger) from four to eight feet broad, and little less in thickness. These mounds are

separated from each other by narrow crooked channels, about six feet deep, most of which intersect the line

of reef at right angles. On the furthest mound, which I was able to reach by the aid of a leapingpole, and

over which the sea broke with some violence, although the day was quite calm and the tide low, the

polypifers in the uppermost cells were all dead, but between three and four inches lower down on its side they

were living, and formed a projecting border round the upper and dead surface. The coral being thus checked

in its upward growth, extends laterally, and hence most of the masses, especially those a little further inwards,

had broad flat dead summits. On the other hand I could see, during the recoil of the breakers, that a few yards

further seaward, the whole convex surface of the Porites was alive; so that the point where we were standing

was almost on the exact upward and shoreward limit of existence of those corals which form the outer margin

of the reef. We shall presently see that there are other organic productions, fitted to bear a somewhat longer

Next, but much inferior in importance to the Porites, is the Millepora complanata. (This Millepora (Palmipora

of Blainville), as well as the M. alcicornis, possesses the singular property of stinging the skin where it is

It grows in thick vertical plates, intersecting each other at various angles, and forms an exceedingly strong

honeycombed mass, which generally affects a circular form, the marginal plates alone being alive. Between

these plates and in the protected crevices on the reef, a multitude of branching zoophytes and other

productions flourish, but the Porites and Millepora alone seem able to resist the fury of the breakers on its

upper and outer edge: at the depth of a few fathoms other kinds of stony corals live. Mr. Liesk, who was

intimately acquainted with every part of this reef, and likewise with that of North Keeling atoll, assured me

that these corals invariably compose the outer margin. The lagoon is inhabited by quite a distinct set of

corals, generally brittle and thinly branched; but a Porites, apparently of the same species with that on the

outside, is found there, although it does not seem to thrive, and certainly does not attain the thousandth part in

The woodcut shows the form of the bottom off the reef: the water deepens for a space between one and two

hundred yards wide, very gradually to twentyfive fathoms (A in section), beyond which the sides plunge

into the unfathomable ocean at an angle of 45 deg. (The soundings from which this section is laid down were

taken with great care by Captain Fitzroy himself. He used a bellshaped lead, having a diameter of four

inches, and the armings each time were cut off and brought on board for me to examine. The arming is a

preparation of tallow, placed in the concavity at the bottom of the lead. Sand, and even small fragments of

rock, will adhere to it; and if the bottom be of rock it brings up an exact impression of its surface.) To the

depth of ten or twelve fathoms the bottom is exceedingly rugged, and seems formed of great masses of living

coral, similar to those on the margin. The arming of the lead here invariably came up quite clean, but deeply

indented, and chains and anchors which were lowered, in the hopes of tearing up the coral, were broken.

Many small fragments, however, of Millepora alcicornis were brought up; and on the arming from an

eightfathom cast, there was a perfect impression of an Astraea, apparently alive. I examined the rolled

fragments cast on the beach during gales, in order further to ascertain what corals grew outside the reef. The

fragments consisted of many kinds, of which the Porites already mentioned and a Madrepora, apparently the

M. corymbosa, were the most abundant. As I searched in vain in the hollows on the reef and in the lagoon, for

a living specimen of this Madrepore, I conclude that it is confined to a zone outside, and beneath the surface,

where it must be very abundant. Fragments of the Millepora alcicornis and of an Astraea were also numerous;

the former is found, but not in proportionate numbers, in the hollows on the reef; but the Astraea I did not see

living. Hence we may infer, that these are the kinds of coral which form the rugged sloping surface

(represented in the woodcut by an uneven line), round and beneath the external margin. Between twelve and

twenty fathoms the arming came up an equal number of times smoothed with sand, and indented with coral:

an anchor and lead were lost at the respective depths of thirteen and sixteen fathoms. Out of twentyfive

soundings taken at a greater depth than twenty fathoms, every one showed that the bottom was covered with

sand; whereas, at a less depth than twelve fathoms, every sounding showed that it was exceedingly rugged,

and free from all extraneous particles. Two soundings were obtained at the depth of 360 fathoms, and several

between two hundred and three hundred fathoms. The sand brought up from these depths consisted of finely

triturated fragments of stony zoophytes, but not, as far as I could distinguish, of a particle of any lamelliform

At a distance of 2,200 yards from the breakers, Captain Fitzroy found no bottom with a line of 7,200 feet in

length; hence the submarine slope of this coral formation is steeper than that of any volcanic cone. Off the

mouth of the lagoon, and likewise off the northern point of the atoll, where the currents act violently, the

inclination, owing to the accumulation of sediment, is less. As the arming of the lead from all the greater

depths showed a smooth sandy bottom, I at first concluded that the whole consisted of a vast conical pile of

calcareous sand, but the sudden increase of depth at some points, and the circumstance of the line having

been cut, as if rubbed, when between five hundred and six hundred fathoms were out, indicate the probable

On the margin of the reef, close within the line where the upper surface of the Porites and of the Millepora is

dead, three species of Nullipora flourish. One grows in thin sheets, like a lichen on old trees; the second in

stony knobs, as thick as a man's finger, radiating from a common centre; and the third, which is less common,

in a mosslike reticulation of thin, but perfectly rigid branches. (This last species is of a beautiful bright

peachblossom colour. Its branches are about as thick as crowquills; they are slightly flattened and knobbed

at the extremities. The extremities only are alive and brightly coloured. The two other species are of a dirty

purplishwhite. The second species is extremely hard; its short knoblike branches are cylindrical, and do

not grow thicker at their extremities.) The three species occur either separately or mingled together; and they

form by their successive growth a layer two or three feet in thickness, which in some cases is hard, but where

formed of the lichenlike kind, readily yields an impression to the hammer: the surface is of a reddish colour.

These Nulliporae, although able to exist above the limit of true corals, seem to require to be bathed during the

greater part of each tide by breaking water, for they are not found in any abundance in the protected hollows

on the back part of the reef, where they might be immersed either during the whole or an equal proportional

time of each tide. It is remarkable that organic productions of such extreme simplicity, for the Nulliporae

undoubtedly belong to one of the lowest classes of the vegetable kingdom, should be limited to a zone so

peculiarly circumstanced. Hence the layer composed by their growth merely fringes the reef for a space of

about twenty yards in width, either under the form of separate mammillated projections, where the outer

masses of coral are separate, or, more commonly, where the corals are united into a solid margin, as a

continuous smooth convex mound (B in woodcut), like an artificial breakwater. Both the mound and

mammillated projections stand about three feet higher than any other part of the reef, by which term I do not

include the islets, formed by the accumulation of rolled fragments. We shall hereafter see that other coral

reefs are protected by a similar thick growth of Nulliporae on the outer margin, the part most exposed to the

The woodcut represents a section across one of the islets on the reef, but if all that part which is above the

level of C were removed, the section would be that of a simple reef, as it occurs where no islet has been

formed. It is this reef which essentially forms the atoll. It is a ring, enclosing the lagoon on all sides except at

the northern end, where there are two open spaces, through one of which ships can enter. The reef varies in

width from two hundred and fifty to five hundred yards, its surface is level, or very slightly inclined towards

the lagoon, and at high tide the sea breaks entirely over it: the water at low tide thrown by the breakers on the

reef, is carried by the many narrow and shoal gullies or channels on its surface, into the lagoon: a return

stream sets out of the lagoon through the main entrance. The most frequent coral in the hollows on the reef is

Pocillopora verrucosa, which grows in short sinuous plates, or branches, and when alive is of a beautiful pale

lakered: a Madrepora, closely allied or identical with M. pocillifera, is also common. As soon as an islet is

formed, and the waves are prevented breaking entirely over the reef, the channels and hollows in it become

filled up with cemented fragments, and its surface is converted into a hard smooth floor (C of woodcut), like

an artificial one of freestone. This flat surface varies in width from one hundred to two hundred, or even three

hundred yards, and is strewed with a few large fragments of coral torn up during gales: it is uncovered only at

low water. I could with difficulty, and only by the aid of a chisel, procure chips of rock from its surface, and

therefore could not ascertain how much of it is formed by the aggregation of detritus, and how much by the

outward growth of mounds of corals, similar to those now living on the margin. Nothing can be more singular

than the appearance at low tide of this "flat" of naked stone, especially where it is externally bounded by the

smooth convex mound of Nulliporae, appearing like a breakwater built to resist the waves, which are

constantly throwing over it sheets of foaming water. The characteristic appearance of this "flat" is shown in

The islets on the reef are first formed between two hundred and three hundred yards from its outer edge,

through the accumulation of a pile of fragments, thrown together by some unusually strong gale. Their

ordinary width is under a quarter of a mile, and their length varies from a few yards to several miles. Those

on the southeast and windward side of the atoll, increase solely by the addition of fragments on their outer

side; hence the loose blocks of coral, of which their surface is composed, as well as the shells mingled with

them, almost exclusively consist of those kinds which live on the outer coast. The highest part of the islets

(excepting hillocks of blown sand, some of which are thirty feet high), is close to the outer beach (E of the

woodcut), and averages from six to ten feet above ordinary highwater mark. From the outer beach the

surface slopes gently to the shores of the lagoon, which no doubt has been caused by the breakers the further

they have rolled over the reef, having had less power to throw up fragments. The little waves of the lagoon

heap up sand and fragments of thinlybranched corals on the inner side of the islets on the leeward side of the

atoll; and these islets are broader than those to windward, some being even eight hundred yards in width; but

the land thus added is very low. The fragments beneath the surface are cemented into a solid mass, which is

exposed as a ledge (D of the woodcut), projecting some yards in front of the outer shore and from two to four

feet high. This ledge is just reached by the waves at ordinary highwater: it extends in front of all the islets,

and everywhere has a waterworn and scooped appearance. The fragments of coral which are occasionally

cast on the "flat" are during gales of unusual violence swept together on the beach, where the waves each day

at highwater tend to remove and gradually wear them down; but the lower fragments having become firmly

cemented together by the percolation of calcareous matter, resist the daily tides longer, and hence project as a

ledge. The cemented mass is generally of a white colour, but in some few parts reddish from ferruginous

matter; it is very hard, and is sonorous under the hammer; it is obscurely divided by seams, dipping at a small

angle seaward; it consists of fragments of the corals which grow on the outer margin, some quite and others

partially rounded, some small and others between two and three feet across; and of masses of previously

formed conglomerate, torn up, rounded, and recemented; or it consists of a calcareous sandstone, entirely

composed of rounded particles, generally almost blended together, of shells, corals, the spines of echini, and

other such organic bodies; rocks, of this latter kind, occur on many shores, where there are no coral reefs. The

structure of the coral in the conglomerate has generally been much obscured by the infiltration of spathose

calcareous matter; and I collected a very interesting series, beginning with fragments of unaltered coral, and

ending with others, where it was impossible to discover with the naked eye any trace of organic structure. In

some specimens I was unable, even with the aid of a lens, and by wetting them, to distinguish the boundaries

of the altered coral and spathose limestone. Many even of the blocks of coral lying loose on the beach, had

The lagoon alone remains to be described; it is much shallower than that of most atolls of considerable size.

The southern part is almost filled up with banks of mud and fields of coral, both dead and alive, but there are

considerable spaces, between three and four fathoms, and smaller basins, from eight to ten fathoms deep.

Probably about half its area consists of sediment, and half of coralreefs. The corals composing these reefs

have a very different aspect from those on the outside; they are very numerous in kind, and most of them are

thinly branched. Meandrina, however, lives in the lagoon, and great rounded masses of this coral are

numerous, lying quite or almost loose on the bottom. The other commonest kinds consist of three closely

allied species of true Madrepora in thin branches; of Seriatapora subulata; two species of Porites (This Porites

has somewhat the habit of P. clavaria, but the branches are not knobbed at their ends. When alive it is of a

yellow colour, but after having been washed in fresh water and placed to dry, a jetblack slimy substance

exuded from the entire surface, so that the specimen now appears as if it had been dipped in ink.) with

cylindrical branches, one of which forms circular clumps, with the exterior branches only alive; and lastly, a

coral something like an Explanaria, but with stars on both surfaces, growing in thin, brittle, stony, foliaceous

expansions, especially in the deeper basins of the lagoon. The reefs on which these corals grow are very

irregular in form, are full of cavities, and have not a solid flat surface of dead rock, like that surrounding the

lagoon; nor can they be nearly so hard, for the inhabitants made with crowbars a channel of considerable

length through these reefs, in which a schooner, built on the S.E. islet, was floated out. It is a very interesting

circumstance, pointed out to us by Mr. Liesk, that this channel, although made less than ten years before our

visit, was then, as we saw, almost choked up with living coral, so that fresh excavations would be absolutely

The sediment from the deepest parts in the lagoon, when wet, appeared chalky, but when dry, like very fine

sand. Large soft banks of similar, but even finer grained mud, occur on the S.E. shore of the lagoon, affording

a thick growth of a Fucus, on which turtle feed: this mud, although discoloured by vegetable matter, appears

from its entire solution in acids to be purely calcareous. I have seen in the Museum of the Geological Society,

a similar but more remarkable substance, brought by Lieutenant Nelson from the reefs of Bermuda, which,

when shown to several experienced geologists, was mistaken by them for true chalk. On the outside of the

reef much sediment must be formed by the action of the surf on the rolled fragments of coral; but in the calm

waters of the lagoon, this can take place only in a small degree. There are, however, other and unexpected

agents at work here: large shoals of two species of Scarus, one inhabiting the surf outside the reef and the

other the lagoon, subsist entirely, as I was assured by Mr. Liesk, the intelligent resident before referred to, by

browsing on the living polypifers. I opened several of these fish, which are very numerous and of

considerable size, and I found their intestines distended by small pieces of coral, and finely ground calcareous

matter. This must daily pass from them as the finest sediment; much also must be produced by the infinitely

numerous vermiform and molluscous animals, which make cavities in almost every block of coral. Dr. J.

Allan, of Forres, who has enjoyed the best means of observation, informs me in a letter that the Holothuriae

(a family of Radiata) subsist on living coral; and the singular structure of bone within the anterior extremity

of their bodies, certainly appears well adapted for this purpose. The number of the species of Holothuria, and

of the individuals which swarm on every part of these coralreefs, is extraordinarily great; and many

shiploads are annually freighted, as is wellknown, for China with the trepang, which is a species of this

genus. The amount of coral yearly consumed, and ground down into the finest mud, by these several

creatures, and probably by many other kinds, must be immense. These facts are, however, of more

importance in another point of view, as showing us that there are living checks to the growth of coralreefs,

and that the almost universal law of "consumed and be consumed," holds good even with the polypifers

forming those massive bulwarks, which are able to withstand the force of the open ocean.

Considering that Keeling atoll, like other coral formations, has been entirely formed by the growth of organic

beings, and the accumulation of their detritus, one is naturally led to inquire how long it has continued, and

how long it is likely to continue, in its present state. Mr. Liesk informed me that he had seen an old chart in

which the present long island on the S.E. side was divided by several channels into as many islets; and he

assures me that the channels can still be distinguished by the smaller size of the trees on them. On several

islets, also, I observed that only young cocoanut trees were growing on the extremities; and that older and

taller trees rose in regular succession behind them; which shows that these islets have very lately increased in

length. In the upper and southeastern part of the lagoon, I was much surprised by finding an irregular field

of at least a mile square of branching corals, still upright, but entirely dead. They consisted of the species

already mentioned; they were of a brown colour, and so rotten, that in trying to stand on them I sank halfway

up the leg, as if through decayed brushwood. The tops of the branches were barely covered by water at the

time of lowest tide. Several facts having led me to disbelieve in any elevation of the whole atoll, I was at first

unable to imagine what cause could have killed so large a field of coral. Upon reflection, however, it

appeared to me that the closing up of the abovementioned channels would be a sufficient cause; for before

this, a strong breeze by forcing water through them into the head of the lagoon, would tend to raise its level.

But now this cannot happen, and the inhabitants observe that the tide rises to a less height, during a high S.E.

wind, at the head than at the mouth of the lagoon. The corals, which, under the former condition of things,

had attained the utmost possible limit of upward growth, would thus occasionally be exposed for a short time

Besides the increase of dry land, indicated by the foregoing facts, the exterior solid reef appears to have

grown outwards. On the western side of the atoll, the "flat" lying between the margin of the reef and the

beach, is very wide; and in front of the regular beach with its conglomerate basis, there is, in most parts, a bed

of sand and loose fragments with trees growing out of it, which apparently is not reached even by the spray at

high water. It is evident some change has taken place since the waves formed the inner beach; that they

formerly beat against it with violence was evident, from a remarkably thick and waterworn point of

conglomerate at one spot, now protected by vegetation and a bank of sand; that they beat against it in the

same peculiar manner in which the swell from windward now obliquely curls round the margin of the reef,

was evident from the conglomerate having been worn into a point projecting from the beach in a similarly

oblique manner. This retreat in the line of action of the breakers might result, either from the surface of the

reef in front of the islets having been submerged at one time, and afterward having grown upwards, or from

the mounds of coral on the margin having continued to grow outwards. That an outward growth of this part is

in process, can hardly be doubted from the fact already mentioned of the mounds of Porites with their

summits apparently lately killed, and their sides only three or four inches lower down thickened by a fresh

layer of living coral. But there is a difficulty on this supposition which I must not pass over. If the whole, or a

large part of the "flat," had been formed by the outward growth of the margin, each successive margin would

naturally have been coated by the Nulliporae, and so much of the surface would have been of equal height

with the existing zone of living Nulliporae: this is not the case, as may be seen in the woodcut. It is, however,

evident from the abraded state of the "flat," with its original inequalities filled up, that its surface has been

much modified; and it is possible that the hinder portions of the zone of Nulliporae, perishing as the reef

grows outwards, might be worn down by the surf. If this has not taken place, the reef can in no part have

increased outwards in breadth since its formation, or at least since the Nulliporae formed the convex mound

on its margin; for the zone thus formed, and which stands between two and three feet above the other parts of

Thus far we have considered facts, which indicate, with more or less probability, the increase of the atoll in

its different parts: there are others having an opposite tendency. On the southeast side, Lieutenant Sulivan,

to whose kindness I am indebted for many interesting observations, found the conglomerate projecting on the

reef nearly fifty yards in front of the beach: we may infer from what we see in all other parts of the atoll, that

the conglomerate was not originally so much exposed, but formed the base of an islet, the front and upper

part of which has since been swept away. The degree to which the conglomerate, round nearly the whole

atoll, has been scooped, broken up, and the fragments cast on the beach, is certainly very surprising, even on

the view that it is the office of occasional gales to pile up fragments, and of the daily tides to wear them

away. On the western side, also, of the atoll, where I have described a bed of sand and fragments with trees

growing out of it, in front of an old beach, it struck both Lieutenant Sulivan and myself, from the manner in

which the trees were being washed down, that the surf had lately recommenced an attack on this line of coast.

Appearances indicating a slight encroachment of the water on the land, are plainer within the lagoon: I

noticed in several places, both on its windward and leeward shores, old cocoanut trees falling with their

roots undermined, and the rotten stumps of others on the beach, where the inhabitants assured us the

cocoanut could not now grow. Captain Fitzroy pointed out to me, near the settlement, the foundation posts

of a shed, now washed by every tide, but which the inhabitants stated, had seven years before stood above

high watermark. In the calm waters of the lagoon, directly connected with a great, and therefore stable ocean,

it seems very improbable that a change in the currents, sufficiently great to cause the water to eat into the land

on all sides, should have taken place within a limited period. From these considerations I inferred, that

probably the atoll had lately subsided to a small amount; and this inference was strengthened by the

circumstance, that in 1834, two years before our visit, the island had been shaken by a severe earthquake, and

by two slighter ones during the ten previous years. If, during these subterranean disturbances, the atoll did

subside, the downward movement must have been very small, as we must conclude from the fields of dead

coral still lipping the surface of the lagoon, and from the breakers on the western shore not having yet

regained the line of their former action. The subsidence must, also, have been preceded by a long period of

rest, during which the islets extended to their present size, and the living margin of the reef grew either

Whether this view be correct or not, the above facts are worthy of attention, as showing how severe a struggle

is in progress on these low coral formations between the two nicely balanced powers of land and water. With

respect to the future state of Keeling atoll, if left undisturbed, we can see that the islets may still extend in

length; but as they cannot resist the surf until broken by rolling over a wide space, their increase in breadth

must depend on the increasing breadth of the reef; and this must be limited by the steepness of the submarine

flanks, which can be added to only by sediment derived from the wear and tear of the coral. From the rapid

growth of the coral in the channel cut for the schooner, and from the several agents at work in producing fine

sediment, it might be thought that the lagoon would necessarily become quickly filled up. Some of this

sediment, however, is transported into the open sea, as appears from the soundings off the mouth of the

lagoon, instead of being deposited within it. The deposition, moreover, of sediment, checks the growth of

coralreefs, so that these two agencies cannot act together with full effect in filling it up. We know so little of

the habits of the many different species of corals, which form the lagoonreefs, that we have no more reasons

for supposing that their whole surface would grow up as quickly as the coral did in the schoonerchannel,

than for supposing that the whole surface of a peatmoss would increase as quickly as parts are known to do

in holes, where the peat has been cut away. These agencies, nevertheless, tend to fill up the lagoon; but in

proportion as it becomes shallower, so must the polypifers be subject to many injurious agencies, such as

impure water and loss of food. For instance, Mr. Liesk informed me, that some years before our visit

unusually heavy rain killed nearly all the fish in the lagoon, and probably the same cause would likewise

injure the corals. The reefs also, it must be remembered, cannot possibly rise above the level of the lowest

springtide, so that the final conversion of the lagoon into land must be due to the accumulation of sediment;

and in the midst of the clear water of the ocean, and with no surrounding high land, this process must be

part.Breaches in the reef.Ledgeformed shores round certain lagoons.Conversion of lagoons into

I will here give a sketch of the general form and structure of the many atolls and atollformed reefs which

occur in the Pacific and Indian Oceans, comparing them with Keeling atoll. The Maldiva atolls and the Great

Chagos Bank differ in so many respects, that I shall devote to them, besides occasional references, a third

section of this chapter. Keeling atoll may be considered as of moderate dimensions and of regular form. Of

the thirtytwo islands surveyed by Captain Beechey in the Low Archipelago, the longest was found to be

thirty miles, and the shortest less than a mile; but Vliegen atoll, situated in another part of the same group,

appears to be sixty miles long and twenty broad. Most of the atolls in this group are of an elongated form;

thus Bow Island is thirty miles in length, and on an average only six in width (See Figure 4, Plate I.), and

Clermont Tonnere has nearly the same proportions. In the Marshall Archipelago (the Ralick and Radack

group of Kotzebue) several of the atolls are more than thirty miles in length, and Rimsky Korsacoff is

fiftyfour long, and twenty wide, at the broadest part of its irregular outline. Most of the atolls in the Maldiva

Archipelago are of great size, one of them (which, however, bears a double name) measured in a medial and

slightly curved line, is no less than eightyeight geographical miles long, its greatest width being under

twenty, and its least only nine and a half miles. Some atolls have spurs projecting from them; and in the

Marshall group there are atolls united together by linear reefs, for instance Menchikoff Island (See Figure 3,

Plate II.), which is sixty miles in length, and consists of three loops tied together. In far the greater number of

cases an atoll consists of a simple elongated ring, with its outline moderately regular.

The average width of the annular wreath may be taken as about a quarter of a mile. Captain Beechey

(Beechey's "Voyage to the Pacific and Beering's Straits," chapter viii.) says that in the atolls of the Low

Archipelago it exceeded in no instance half a mile. The description given of the structure and proportional

dimensions of the reef and islets of Keeling atoll, appears to apply perfectly to nearly all the atolls in the

Pacific and Indian Oceans. The islets are first formed some way back either on the projecting points of the

reef, especially if its form be angular, or on the sides of the main entrances into the lagoonthat is in both

cases, on points where the breakers can act during gales of wind in somewhat different directions, so that the

matter thrown up from one side may accumulate against that before thrown up from another. In Lutke's chart

of the Caroline atolls, we see many instances of the former case; and the occurrence of islets, as if placed for

beacons, on the points where there is a gateway or breach through the reef, has been noticed by several

authors. There are some atollformed reefs, rising to the surface of the sea and partly dry at low water, on

which from some cause islets have never been formed; and there are others on which they have been formed,

but have subsequently been worn away. In atolls of small dimensions the islets frequently become united into

a single horseshoe or ringformed strip; but Diego Garcia, although an atoll of considerable size, being

thirteen miles and a half in length, has its lagoon entirely surrounded, except at the northern end, by a belt of

land, on an average a third of a mile in width. To show how small the total area of the annular reef and the

land is in islands of this class, I may quote a remark from the voyage of Lutke, namely, that if the fortythree

rings, or atolls, in the Caroline Archipelago, were put one within another, and over a steeple in the centre of

The form of the bottom off Keeling atoll, which gradually slopes to about twenty fathoms at the distance of

between one and two hundred yards from the edge of the reef, and then plunges at an angle of 45 deg into

unfathomable depths, is exactly the same (The form of the bottom round the Marshall atolls in the Northern

Pacific is probably similar: Kotzebue ("First Voyage," volume ii., page 16) says: "We had at a small distance

from the reef, forty fathoms depth, which increased a little further so much that we could find no bottom.")

with that of the sections of the atolls in the Low Archipelago given by Captain Beechey. The nature,

however, of the bottom seems to differ, for this officer (I must be permitted to express my obligation to

Captain Beechey, for the very kind manner in which he has given me information on several points, and to

own the great assistance I have derived from his excellent published work.) informs me that all the soundings,

even the deepest, were on coral, but he does not know whether dead or alive. The slope round Christmas atoll

(Lat. 1 deg 4' N., 157 deg 45' W.), described by Cook (Cook's "Third Voyage," volume ii., chapter 10.), is

considerably less, at about half a mile from the edge of the reef, the average depth was about fourteen

fathoms on a fine sandy bottom, and at a mile, only between twenty and forty fathoms. It has no doubt been

owing to this gentle slope, that the strip of land surrounding its lagoon, has increased in one part to the

extraordinary width of three miles; it is formed of successive ridges of broken shells and corals, like those on

the beach. I know of no other instance of such width in the reef of an atoll; but Mr. F.D. Bennett informs me

that the inclination of the bottom round Caroline atoll in the Pacific, is like that off Christmas Island, very

gentle. Off the Maldiva and Chagos atolls, the inclination is much more abrupt; thus at Heawandoo Pholo,

Lieutenant Powell (This fact is taken from a MS. account of these groups lent me by Captain Moresby. See

also Captain Moresby's paper on the Maldiva atolls in the "Geographical Journal", volume v., page 401.)

found fifty and sixty fathoms close to the edge of the reef, and at 300 yards distance there was no bottom with

a 300yard line. Captain Moresby informs me, that at 100 fathoms from the mouth of the lagoon of Diego

Garcia, he found no bottom with 150 fathoms; this is the more remarkable, as the slope is generally less

abrupt in front of channels through a reef, owing to the accumulation of sediment. At Egmont Island, also, at

150 fathoms from the reef, soundings were struck with 150 fathoms. Lastly, at Cardoo atoll, only sixty yards

from the reef, no bottom was obtained, as I am informed by Captain Moresby, with a line of 200 fathoms!

The currents run with great force round these atolls, and where they are strongest, the inclination appears to

be most abrupt. I am informed by the same authority, that wherever soundings were obtained off these

islands, the bottom was invariably sandy: nor was there any reason to suspect the existence of submarine

cliffs, as there was at Keeling Island. (Off some of the islands in the Low Archipelago the bottom appears to

descend by ledges. Off Elizabeth Island, which, however, consists of raised coral, Captain Beechey (page 45,

4to edition) describes three ledges: the first had an easy slope from the beach to a distance of about fifty

yards: the second extended two hundred yards with twentyfive fathoms on it, and then ended abruptly, like

the first; and immediately beyond this there was no bottom with two hundred fathoms.) Here then occurs a

difficulty; can sand accumulate on a slope, which, in some cases, appears to exceed fiftyfive degrees? It

must be observed, that I speak of slopes where soundings were obtained, and not of such cases, as that of

Cardoo, where the nature of the bottom is unknown, and where its inclination must be nearly vertical. M. Elie

de Beaumont ("Memoires pour servir a une description Geolog. de France," tome iv., page 216.) has argued,

and there is no higher authority on this subject, from the inclination at which snow slides down in avalanches,

that a bed of sand or mud cannot be formed at a greater angle than thirty degrees. Considering the number of

soundings on sand, obtained round the Maldiva and Chagos atolls, which appears to indicate a greater angle,

and the extreme abruptness of the sandbanks in the West Indies, as will be mentioned in the Appendix, I

must conclude that the adhesive property of wet sand counteracts its gravity, in a much greater ratio than has

been allowed for by M. Elie de Beaumont. From the facility with which calcareous sand becomes

agglutinated, it is not necessary to suppose that the bed of loose sand is thick.

Captain Beechey has observed, that the submarine slope is much less at the extremities of the more elongated

atolls in the Low Archipelago, than at their sides; in speaking of Ducie's Island he says (Beechey's "Voyage,"

4to edition, page 44.) the buttress, as it may be called, which "has the most powerful enemy (the S.W. swell)

to oppose, is carried out much further, and with less abruptness than the other." In some cases, the less

inclination of a certain part of the external slope, for instance of the northern extremities of the two Keeling

atolls, is caused by a prevailing current which there accumulates a bed of sand. Where the water is perfectly

tranquil, as within a lagoon, the reefs generally grow up perpendicularly, and sometimes even overhang their

bases; on the other hand, on the leeward side of Mauritius, where the water is generally tranquil, although not

invariably so, the reef is very gently inclined. Hence it appears that the exterior angle varies much;

nevertheless in the close similarity in form between the sections of Keeling atoll and of the atolls in the Low

Archipelago, in the general steepness of the reefs of the Maldiva and Chagos atolls, and in the

perpendicularity of those rising out of water always tranquil, we may discern the effects of uniform laws; but

from the complex action of the surf and currents, on the growing powers of the coral and on the deposition of

Where islets have been formed on the reef, that part which I have sometimes called the "flat" and which is

partly dry at low water, appears similar in every atoll. In the Marshall group in the North Pacific, it may be

inferred from Chamisso's description, that the reef, where islets have not been formed on it, slopes gently

from the external margin to the shores of the lagoon; Flinders states that the Australian barrier has a similar

inclination inwards, and I have no doubt it is of general occurrence, although, according to Ehrenberg, the

reefs of the Red Sea offer an exception. Chamisso observes that "the red colour of the reef (at the Marshall

atolls) under the breakers is caused by a Nullipora, which covers the stone WHEREVER THE WAVES

BEAT; and, under favourable circumstances, assumes a stalactical form,"a description perfectly applicable

to the margin of Keeling atoll. (Kotzebue's "First Voyage," volume iii., page 142. Near Porto Praya, in the

Cape de Verde Islands, some basaltic rocks, lashed by no inconsiderable surf, were completely enveloped

with a layer of Nulliporae. The entire surface over many square inches, was coloured of a peachblossomed

red; the layer, however, was of no greater thickness than paper. Another kind, in the form of projecting

knobs, grew in the same situation. These Nulliporae are closely related to those described on the coralreefs,

but I believe are of different species.) Although Chamisso does not state that the masses of Nulliporae form

points or a mound, higher than the flat, yet I believe that this is the case; for Kotzebue (Kotzebue, "First

Voyage," volume ii., page 16. Lieutenant Nelson, in his excellent memoir in the Geological Transactions

(volume ii., page 105), alludes to the rocky points mentioned by Kotzebue, and infers that they consist of

Serpulae, which compose incrusting masses on the reefs of Bermudas, as they likewise do on a sandstone bar

off the coast of Brazil (which I have described in "London Phil. Journal," October 1841). These masses of

Serpulae hold the same position, relatively to the action of the sea, with the Nulliporae on the coralreefs in

the Indian and Pacific Oceans.), in another part, speaks of the rocks on the edge of the reef "as visible for

about two feet at low water," and these rocks we may feel quite certain are not formed of true coral (Captain

Moresby, in his valuable paper "on the Northern atolls of Maldivas" ("Geographical Journal", volume v.),

says that the edges of the reefs there stand above water at low springtides.) Whether a smooth convex

mound of Nulliporae, like that which appears as if artificially constructed to protect the margin of Keeling

Island, is of frequent occurrence round atolls, I know not; but we shall presently meet with it, under precisely

the same form, on the outer edge of the "barrierreefs" which encircle the Society Islands.

There appears to be scarcely a feature in the structure of Keeling reef, which is not of common, if not of

universal occurrence, in other atolls. Thus Chamisso describes (Kotzebue's "First Voyage," volume iii., page

144.) a layer of coarse conglomerate, outside the islets round the Marshall atolls which "appears on its upper

surface uneven and eaten away." From drawings, with appended remarks, of Diego Garcia in the Chagos

group and of several of the Maldiva atolls, shown me by Captain Moresby (see also Moresby on the Northern

atolls of the Maldivas, "Geographical Journal", volume v., page 400.), it is evident that their outer coasts are

subject to the same round of decay and renovation as those of Keeling atoll. From the description of the atolls

in the Low Archipelago, given in Captain Beechey's "Voyage," it is not apparent that any conglomerate

The lagoon in Keeling atoll is shallow; in the atolls of the Low Archipelago the depth varies from 20 to 38

fathoms, and in the Marshall Group, according to Chamisso, from 30 to 35; in the Caroline atolls it is only a

little less. Within the Maldiva atolls there are large spaces with 45 fathoms, and some soundings are laid

down of 49 fathoms. The greater part of the bottom in most lagoons, is formed of sediment; large spaces have

exactly the same depth, or the depth varies so insensibly, that it is evident that no other means, excepting

aqueous deposition, could have leveled the surface so equally. In the Maldiva atolls this is very conspicuous,

and likewise in some of the Caroline and Marshall Islands. In the former large spaces consist of sand and

SOFT CLAY; and Kotzebue speaks of clay having been found within one of the Marshall atolls. No doubt

this clay is calcareous mud, similar to that at Keeling Island, and to that at Bermuda already referred to, as

undistinguishable from disintegrated chalk, and which Lieutenant Nelson says is called there pipeclay. (I

may here observe that on the coast of Brazil, where there is much coral, the soundings near the land are

described by Admiral Roussin, in the "Pilote du Bresil", as siliceous sand, mingled with much finely

comminuted particles of shells and coral. Further in the offing, for a space of 1,300 miles along the coast,

from the Abrolhos Islands to Maranham, the bottom in many places is composed of "tuf blanc, mele ou forme

de madrepores broyes." This white substance, probably, is analogous to that which occurs within the

abovementioned lagoons; it is sometimes, according to Roussin, firm, and he compares it to mortar.)

Where the waves act with unequal force on the two sides of an atoll, the islets appear to be first formed, and

are generally of greater continuity on the more exposed shore. The islets, also, which are placed to leeward,

are in most parts of the Pacific liable to be occasionally swept entirely away by gales, equalling hurricanes in

violence, which blow in an opposite direction to the ordinary tradewind. The absence of the islets on the

leeward side of atolls, or when present their lesser dimensions compared with those to windward, is a

comparatively unimportant fact; but in several instances the reef itself on the leeward side, retaining its usual

defined outline, does not rise to the surface by several fathoms. This is the case with the southern side of

Peros Banhos (Plate I., Figure 9) in the Chagos group, with Mourileu atoll (Frederick Lutke's "Voyage autour

du Monde," volume ii., page 291. See also his account of Namonouito, below, and the chart of Oulleay in the

Atlas.) in the Caroline Archipelago, and with the barrierreef (Plate I., Figure 8) of the Gambier Islands. I

allude to the latter reef, although belonging to another class, because Captain Beechey was first led by it to

observe the peculiarity in the question. At Peros Banhos the submerged part is nine miles in length, and lies

at an average depth of about five fathoms; its surface is nearly level, and consists of hard stone, with a thin

covering of loose sand. There is scarcely any living coral on it, even on the outer margin, as I have been

particularly assured by Captain Moresby; it is, in fact, a wall of dead coralrock, having the same width and

transverse section with the reef in its ordinary state, of which it is a continuous portion. The living and perfect

parts terminate abruptly, and abut on the submerged portions, in the same manner as on the sides of an

ordinary passage through the reef. The reef to leeward in other cases is nearly or quite obliterated, and one

side of the lagoon is left open; for instance, at Oulleay (Caroline Archipelago), where a crescentformed reef

is fronted by an irregular bank, on which the other half of the annular reef probably once stood. At

Namonouito, in the same Archipelago, both these modifications of the reef concur; it consists of a great flat

bank, with from twenty to twentyfive fathoms water on it; for a length of more than forty miles on its

southern side it is open and without any reef, whilst on the other sides it is bounded by a reef, in parts rising

to the surface and perfectly characterised, in parts lying some fathoms submerged. In the Chagos group there

are annular reefs, entirely submerged, which have the same structure as the submerged and defined portions

just described. The Speaker's Bank offers an excellent example of this structure; its central expanse, which is

about twentytwo fathoms deep, is twentyfour miles across; the external rim is of the usual width of annular

reefs, and is welldefined; it lies between six and eight fathoms beneath the surface, and at the same depth

there are scattered knolls in the lagoon. Captain Moresby believes the rim consists of dead rock, thinly

covered with sand, and he is certain this is the case with the external rim of the Great Chagos Bank, which is

also essentially a submerged atoll. In both these cases, as in the submerged portion of the reef at Peros

Banhos, Captain Moresby feels sure that the quantity of living coral, even on the outer edge overhanging the

deepsea water, is quite insignificant. Lastly, in several parts of the Pacific and Indian Oceans there are

banks, lying at greater depths than in the cases just mentioned, of the same form and size with the

neighbouring atolls, but with their atolllike structure wholly obliterated. It appears from the survey of

Freycinet, that there are banks of this kind in the Caroline Archipelago, and, as is reported, in the Low

Archipelago. When we discuss the origin of the different classes of coral formations, we shall see that the

submerged state of the whole of some atollformed reefs, and of portions of others, generally but not

invariably on the leeward side, and the existence of more deeply submerged banks now possessing little or no

signs of their original atolllike structure, are probably the effects of a uniform cause,namely, the death of

the coral, during the subsidence of the area, in which the atolls or banks are situated.

There is seldom, with the exception of the Maldiva atolls, more than two or three channels, and generally

only one leading into the lagoon, of sufficient depth for a ship to enter. in small atolls, there is usually not

even one. Where there is deep water, for instance above twenty fathoms, in the middle of the lagoon, the

channels through the reef are seldom as deep as the centre,it may be said that the rim only of the

saucershaped hollow forming the lagoon is notched. Mr. Lyell ("Principles of Geology," volume iii., page

289.) has observed that the growth of the coral would tend to obstruct all the channels through a reef, except

those kept open by discharging the water, which during high tide and the greater part of each ebb is thrown

over its circumference. Several facts indicate that a considerable quantity of sediment is likewise discharged

through these channels; and Captain Moresby informs me that he has observed, during the change of the

monsoon, the sea discoloured to a distance off the entrances into the Maldiva and Chagos atolls. This,

probably, would check the growth of the coral in them, far more effectually than a mere current of water. In

the many small atolls without any channel, these causes have not prevented the entire ring attaining the

surface. The channels, like the submerged and effaced parts of the reef, very generally though not invariably

occur on the leeward side of the atoll, or on that side, according to Beechey (Beechey's "Voyage," 4to edition,

volume i., page 189.), which, from running in the same direction with the prevalent wind, is not fully exposed

to it. Passages between the islets on the reef, through which boats can pass at high water, must not be

confounded with shipchannels, by which the annular reef itself is breached. The passages between the islets

occur, of course, on the windward as well as on the leeward side; but they are more frequent and broader to

At Keeling atoll the shores of the lagoon shelve gradually, where the bottom is of sediment, and irregularly or

abruptly where there are coralreefs; but this is by no means the universal structure in other atolls. Chamisso

(Kotzebue's "First Voyage," volume iii., page 142.), speaking in general terms of the lagoons in the Marshall

atolls, says the lead generally sinks "from a depth of two or three fathoms to twenty or twentyfour, and you

may pursue a line in which on one side of the boat you may see the bottom, and on the other the azureblue

deep water." The shores of the lagoonlike channel within the barrierreef at Vanikoro have a similar

structure. Captain Beechey has described a modification of this structure (and he believes it is not

uncommon) in two atolls in the Low Archipelago, in which the shores of the lagoon descend by a few, broad,

slightly inclined ledges or steps: thus at Matilda atoll (Beechey's "Voyage," 4to edition, volume i, page 160.

At Whitsunday Island the bottom of the lagoon slopes gradually towards the centre, and then deepens

suddenly, the edge of the bank being nearly perpendicular. This bank is formed of coral and dead shells.), the

great exterior reef, the surface of which is gently inclined towards and beneath the surface of the lagoon, ends

abruptly in a little cliff three fathoms deep; at its foot, a ledge forty yards wide extends, shelving gently

inwards like the surfacereef, and terminated by a second little cliff five fathoms deep; beyond this, the

bottom of the lagoon slopes to twenty fathoms, which is the average depth of its centre. These ledges seem to

be formed of coralrock; and Captain Beechey says that the lead often descended several fathoms through

holes in them. In some atolls, all the coral reefs or knolls in the lagoon come to the surface at low water; in

other cases of rarer occurrence, all lie at nearly the same depth beneath it, but most frequently they are quite

irregular,some with perpendicular, some with sloping sides,some rising to the surface, and others lying

at all intermediate depths from the bottom upwards. I cannot, therefore, suppose that the union of such reefs

could produce even one uniformly sloping ledge, and much less two or three, one beneath the other, and each

terminated by an abrupt wall. At Matilda Island, which offers the best example of the steplike structure,

Captain Beechey observes that the coralknolls within the lagoon are quite irregular in their height. We shall

hereafter see that the theory which accounts for the ordinary form of atolls, apparently includes this

In the midst of a group of atolls, there sometimes occur small, flat, very low islands of coral formation, which

probably once included a lagoon, since filled up with sediment and coralreefs. Captain Beechey entertains

no doubt that this has been the case with the two small islands, which alone of thirtyone surveyed by him in

the Low Archipelago, did not contain lagoons. Romanzoff Island (in lat. 15 deg S.) is described by Chamisso

(Kotzebue's "First Voyage," volume iii., page 221.) as formed by a dam of madreporitic rock inclosing a flat

space, thinly covered with trees, into which the sea on the leeward side occasionally breaks. North Keeling

atoll appears to be in a rather less forward stage of conversion into land; it consists of a horseshoe shaped

strip of land surrounding a muddy flat, one mile in its longest axis, which is covered by the sea only at high

water. When describing South Keeling atoll, I endeavoured to show how slow the final process of filling up a

lagoon must be; nevertheless, as all causes do tend to produce this effect, it is very remarkable that not one

instance, as I believe, is known of a moderately sized lagoon being filled up even to the low waterline at

springtides, much less of such a one being converted into land. It is, likewise, in some degree remarkable,

how few atolls, except small ones, are surrounded by a single linear strip of land, formed by the union of

separate islets. We cannot suppose that the many atolls in the Pacific and Indian Oceans all have had a late

origin, and yet should they remain at their present level, subjected only to the action of the sea and to the

growing powers of the coral, during as many centuries as must have elapsed since any of the earlier tertiary

epochs, it cannot, I think, be doubted that their lagoons and the islets on their reef, would present a totally

different appearance from what they now do. This consideration leads to the suspicion that some renovating

agency (namely subsidence) comes into play at intervals, and perpetuates their original structure.

FIGURE 1.GREAT CHAGOS BANK, in the Indian Ocean; taken from the survey by Captain Moresby

and Lieutenant Powell; the parts which are shaded, with the exception of two or three islets on the western

and northern sides, do not rise to the surface, but are submerged from four to ten fathoms; the banks bounded

by the dotted lines lie from fifteen to twenty fathoms beneath the surface, and are formed of sand; the central

FIGURE 2.A vertical section, on the same scale, in an eastern and western line across the Great Chagos

FIGURE 3.MENCHIKOFF ATOLL (or lagoonisland), in the Marshall Archipelago, Northern Pacific

Ocean; from Krusenstern's "Atlas of the Pacific;" originally surveyed by Captain Hagemeister; the depth

FIGURE 4.MAHLOS MAHDOO ATOLL, together with Horsburgh atoll, in the Maldiva Archipelago;

from the survey by Captain Moresby and Lieutenant Powell; the white spaces in the middle of the separate

small reefs, both on the margin and in the middle part, are meant to represent little lagoons; but it was found

not possible to distinguish them clearly from the small islets, which have been formed on these same small

reefs; many of the smaller reefs could not be introduced; the nautical mark (dot over a dash) over the figures

250 and 200, between Mahlos Mahdoo and Horsburgh atoll and Powell's island, signifies that soundings were

FIGURE 5.NEW CALEDONIA, in the western part of the Pacific; from Krusenstern's "Atlas," compiled

from several surveys; I have slightly altered the northern point of the reef, in accordance with the "Atlas of

the Voyage of the 'Astrolabe'." In Krusenstern's "Atlas," the reef is represented by a single line with crosses; I

FIGURE 6.MALDIVA ARCHIPELAGO, in the Indian Ocean; from the survey by Captain Moresby and

Maldiva Archipelago.Ringformed reefs, marginal and central.Great depths in the lagoons of the

southern atolls.Reefs in the lagoons all rising to the surface.Position of islets and breaches in the reefs,

with respect to the prevalent winds and action of the waves.Destruction of islets.Connection in the

position and submarine foundation of distinct atolls.The apparent disseverment of large atolls.The Great

Although occasional references have been made to the Maldiva atolls, and to the banks in the Chagos group,

some points of their structure deserve further consideration. My description is derived from an examination

of the admirable charts lately published from the survey of Captain Moresby and Lieutenant Powell, and

more especially from information which Captain Moresby has communicated to me in the kindest manner.

The Maldiva Archipelago is 470 miles in length, with an average breadth of about 50 miles. The form and

dimensions of the atolls, and their singular position in a double line, may be seen, but not well, in the greatly

reduced chart (Figure 6) in Plate II. The dimensions of the longest atoll in the group (called by the double

name of MilladouMadou and TilladouMatte) have already been given; it is 88 miles in a medial and

slightly curved line, and is less than 20 miles in its broadest part. Suadiva, also, is a noble atoll, being 44

miles across in one direction, and 34 in another, and the great included expanse of water has a depth of

between 250 and 300 feet. The smaller atolls in this group differ in no respect from ordinary ones; but the

larger ones are remarkable from being breached by numerous deepwater channels leading into the lagoon;

for instance, there are 42 channels, through which a ship could enter the lagoon of Suadiva. In the three

southern large atolls, the separate portions of reef between these channels have the ordinary structure, and are

linear; but in the other atolls, especially the more northern ones, these portions are ring formed, like

miniature atolls. Other ringformed reefs rise out of the lagoons, in the place of those irregular ones which

ordinarily occur there. In the reduction of the chart of Mahlos Mahdoo (Plate II., Figure 4), it was not found

easy to define the islets and the little lagoons within each reef, so that the ringformed structure is very

imperfectly shown; in the large published charts of TilladouMatte, the appearance of these rings, from

standing further apart from each other, is very remarkable. The rings on the margin are generally elongated;

many of them are three, and some even five miles, in diameter; those within the lagoon are usually smaller,

few being more than two miles across, and the greater number rather less than one. The depth of the little

lagoon within these small annular reefs is generally from five to seven fathoms, but occasionally more; and in

Ari atoll many of the central ones are twelve, and some even more than twelve fathoms deep. These rings rise

abruptly from the platform or bank, on which they are placed; their outer margin is invariably bordered by

living coral (Captain Moresby informs me that Millepora complanata is one of the commonest kinds on the

outer margin, as it is at Keeling atoll.) within which there is a flat surface of coral rock; of this flat, sand and

fragments have in many cases accumulated and been converted into islets, clothed with vegetation. I can, in

fact, point out no essential difference between these little ringformed reefs (which, however, are larger, and

contain deeper lagoons than many true atolls that stand in the open sea), and the most perfectly characterised

atolls, excepting that the ringformed reefs are based on a shallow foundation, instead of on the floor of the

open sea, and that instead of being scattered irregularly, they are grouped closely together on one large

The perfect series which can be traced from portions of simple linear reef, to others including long linear

lagoons, and from these again to oval or almost circular rings, renders it probable that the latter are merely

modifications of the linear or normal state. It is conformable with this view, that the ringformed reefs on the

margin, even where most perfect and standing furthest apart, generally have their longest axes directed in the

line which the reef would have held, if the atoll had been bounded by an ordinary wall. We may also infer

that the central ringformed reefs are modifications of those irregular ones, which are found in the lagoons of

all common atolls. It appears from the charts on a large scale, that the ringlike structure is contingent on the

marginal channels or breaches being wide; and, consequently, on the whole interior of the atoll being freely

exposed to the waters of the open sea. When the channels are narrow or few in number, although the lagoon

be of great size and depth (as in Suadiva), there are no ringformed reefs; where the channels are somewhat

broader, the marginal portions of reef, and especially those close to the larger channels, are ringformed, but

the central ones are not so; where they are broadest, almost every reef throughout the atoll is more or less

perfectly ringformed. Although their presence is thus contingent on the openness of the marginal channels,

the theory of their formation, as we shall hereafter see, is included in that of the parent atolls, of which they

The lagoons of all the atolls in the southern part of the Archipelago are from ten to twenty fathoms deeper

than those in the northern part. This is well exemplified in the case of Addoo, the southernmost atoll in the

group, for although only nine miles in its longest diameter, it has a depth of thirtynine fathoms, whereas all

the other small atolls have comparatively shallow lagoons; I can assign no adequate cause for this difference

in depth. In the central and deepest part of the lagoons, the bottom consists, as I am informed by Captain

Moresby, of stiff clay (probably a calcareous mud); nearer the border it consists of sand, and in the channels

through the reef, of hard sandbanks, sandstone, conglomerate rubble, and a little live coral. Close outside

the reef and the line joining its detached portions (where intersected by many channels), the bottom is sandy,

and it slopes abruptly into unfathomable depths. In most lagoons the depth is considerably greater in the

centre than in the channels; but in TilladouMatte, where the marginal ringformed reefs stand far apart, the

same depth is carried across the entire atoll, from the deepwater line on one side to that on the other. I

cannot refrain from once again remarking on the singularity of these atolls,a great sandy and generally

concave disc rises abruptly from the unfathomable ocean, with its central expanse studded and its border

symmetrically fringed with oval basins of coralrock, just lipping the surface of the sea, sometimes clothed

In the southern Maldiva atolls, of which there are nine large ones, all the small reefs within the lagoons come

to the surface, and are dry at low water springtides; hence in navigating them, there is no danger from

submarine banks. This circumstance is very remarkable, as within some atolls, for instance those of the

neighbouring Chagos group, not a single reef comes to the surface, and in most other cases a few only do, and

the rest lie at all intermediate depths from the bottom upwards. When treating of the growth of coral I shall

Although in the neighbourhood of the Maldiva Archipelago the winds, during the monsoons, blow during

nearly an equal time from opposite quarters, and although, as I am informed by Captain Moresby, the

westerly winds are the strongest, yet the islets are almost all placed on the eastern side of the northern atolls,

and on the southeastern side of the southern atolls. That the formation of the islets is due to detritus thrown

up from the outside, as in the ordinary manner, and not from the interior of the lagoons, may, I think be safely

inferred from several considerations, which it is hardly worth while to detail. As the easterly winds are not

the strongest, their action probably is aided by some prevailing swell or current.

In groups of atolls, exposed to a tradewind, the shipchannels into the lagoons are almost invariably situated

on the leeward or less exposed side of the reef, and the reef itself is sometimes either wanting there, or is

submerged. A strictly analogous, but different fact, may be observed at the Maldiva atollsnamely, that

where two atolls stand in front of each other, the breaches in the reef are the most numerous on their near, and

therefore less exposed, sides. Thus on the near sides of Ari and the two Nillandoo atolls, which face S. Male,

Phaleedoo, and Moloque atolls, there are seventythree deepwater channels, and only twentyfive on their

outer sides; on the near side of the three latter named atolls there are fifty six openings, and only

thirtyseven on their outsides. It is scarcely possible to attribute this difference to any other cause than the

somewhat different action of the sea on the two sides, which would ensue from the protection afforded by the

two rows of atolls to each other. I may here remark that in most cases, the conditions favourable to the greater

accumulation of fragments on the reef and to its more perfect continuity on one side of the atoll than on the

other, have concurred, but this has not been the case with the Maldivas; for we have seen that the islets are

placed on the eastern or southeastern sides, whilst the breaches in the reef occur indifferently on any side,

where protected by an opposite atoll. The reef being more continuous on the outer and more exposed sides of

those atolls which stand near each other, accords with the fact, that the reef of the southern atolls is more

continuous than that of the northern ones; for the former, as I am informed by Captain Moresby, are more

The date of the first formation of some of the islets in this Archipelago is known to the inhabitants; on the

other hand, several islets, and even some of those which are believed to be very old, are now fast wearing

away. The work of destruction has, in some instances, been completed in ten years. Captain Moresby found

on one waterwashed reef the marks of wells and graves, which were excavated when it supported an islet. In

South Nillandoo atoll, the natives say that three of the islets were formerly larger: in North Nillandoo there is

one now being washed away; and in this latter atoll Lieutenant Prentice found a reef, about six hundred yards

in diameter, which the natives positively affirmed was lately an island covered with cocoanut trees. It is

now only partially dry at low water springtides, and is (in Lieutenant Prentice's words) "entirely covered

with live coral and madrepore." In the northern part, also, of the Maldiva Archipelago and in the Chagos

group, it is known that some of the islets are disappearing. The natives attribute these effects to variations in

the currents of the sea. For my own part I cannot avoid suspecting that there must be some further cause,

which gives rise to such a cycle of change in the action of the currents of the great and open ocean.

Several of the atolls in this Archipelago are so related to each other in form and position, that at the first

glance one is led to suspect that they have originated in the disseverment of a single one. Male consists of

three perfectly characterised atolls, of which the shape and relative position are such, that a line drawn closely

round all three, gives a symmetrical figure; to see this clearly, a larger chart is required than that of the

Archipelago in Plate II.; the channel separating the two northern Male atolls is only little more than a mile

wide, and no bottom was found in it with 100 fathoms. Powell's Island is situated at the distance of two miles

and a half off the northern end of Mahlos Mahdoo (see Figure 4, Plate II.), at the exact point where the two

sides of the latter, if prolonged, would meet; no bottom, however, was found in the channel with 200

fathoms; in the wider channel between Horsburgh atoll and the southern end of Mahlos Mahdoo, no bottom

was found with 250 fathoms. In these and similar cases, the relation consists only in the form and position of

the atolls. But in the channel between the two Nillandoo atolls, although three miles and a quarter wide,

soundings were struck at the depth of 200 fathoms; the channel between Ross and Ari atolls is four miles

wide, and only 150 fathoms deep. Here then we have, besides the relation of form, a submarine connection.

The fact of soundings having been obtained between two separate and perfectly characterised atolls is in itself

interesting, as it has never, I believe, been effected in any of the many other groups of atolls in the Pacific and

Indian seas. In continuing to trace the connection of adjoining atolls, if a hasty glance be taken at the chart

(Figure 4., Plate II.) of Mahlos Mahdoo, and the line of unfathomable water be followed, no one will hesitate

to consider it as one atoll. But a second look will show that it is divided by a bifurcating channel, of which

the northern arm is about one mile and threequarters in width, with an average depth of 125 fathoms, and

the southern one threequarters of a mile wide, and rather less deep. These channels resemble in the slope of

their sides and general form, those which separate atolls in every respect distinct; and the northern arm is

wider than that dividing two of the Male atolls. The ringformed reefs on the sides of this bifurcating channel

are elongated, so that the northern and southern portions of Mahlos Mahdoo may claim, as far as their

external outline is concerned, to be considered as distinct and perfect atolls. But the intermediate portion,

lying in the fork of the channel, is bordered by reefs less perfect than those which surround any other atoll in

the group of equally small dimensions. Mahlos Mahdoo, therefore, is in every respect in so intermediate a

condition, that it may be considered either as a single atoll nearly dissevered into three portions, or as three

atolls almost perfect and intimately connected. This is an instance of a very early stage of the apparent

disseverment of an atoll, but a still earlier one in many respects is exhibited at Tilladou Matte. In one part

of this atoll, the ringformed reefs stand so far apart from each other, that the inhabitants have given different

names to the northern and southern halves; nearly all the rings, moreover, are so perfect and stand so

separate, and the space from which they rise is so level and unlike a true lagoon, that we can easily imagine

the conversion of this one great atoll, not into two or three portions, but into a whole group of miniature

atolls. A perfect series such as we have here traced, impresses the mind with an idea of actual change; and it

will hereafter be seen, that the theory of subsidence, with the upward growth of the coral, modified by

accidents of probable occurrence, will account for the occasional disseverment of large atolls.

The Great Chagos bank alone remains to be described. In the Chagos group there are some ordinary atolls,

some annular reefs rising to the surface but without any islets on them, and some atollformed banks, either

quite submerged, or nearly so. Of the latter, the Great Chagos Bank is much the largest, and differs in its

structure from the others: a plan of it is given in Plate II., Figure 1, in which, for the sake of clearness, I have

had the parts under ten fathoms deep finely shaded: an east and west vertical section is given in Figure 2, in

which the vertical scale has been necessarily exaggerated. Its longest axis is ninety nautical miles, and

another line drawn at right angles to the first, across the broadest part, is seventy. The central part consists of

a level muddy flat, between forty and fifty fathoms deep, which is surrounded on all sides, with the exception

of some breaches, by the steep edges of a set of banks, rudely arranged in a circle. These banks consist of

sand, with a very little live coral; they vary in breadth from five to twelve miles, and on an average lie about

sixteen fathoms beneath the surface; they are bordered by the steep edges of a third narrow and upper bank,

which forms the rim to the whole. This rim is about a mile in width, and with the exception of two or three

spots where islets have been formed, is submerged between five and ten fathoms. It consists of smooth hard

rock, covered with a thin layer of sand, but with scarcely any live coral; it is steep on both sides, and

outwards slopes abruptly into unfathomable depths. At the distance of less than half a mile from one part, no

bottom was found with 190 fathoms; and off another point, at a somewhat greater distance, there was none

with 210 fathoms. Small steepsided banks or knolls, covered with luxuriantly growing coral, rise from the

interior expanse to the same level with the external rim, which, as we have seen, is formed only of dead rock.

It is impossible to look at the plan (Figure 1, Plate II.), although reduced to so small a scale, without at once

perceiving that the Great Chagos Bank is, in the words of Captain Moresby (This officer has had the kindness

to lend me an excellent MS. account of the Chagos Islands; from this paper, from the published charts, and

from verbal information communicated to me by Captain Moresby, the above account of the Great Chagos

Bank is taken.), "nothing more than a halfdrowned atoll." But of what great dimensions, and of how

extraordinary an internal structure? We shall hereafter have to consider both the cause of its submerged

condition, a state common to other banks in the group, and the origin of the singular submarine terraces,

which bound the central expanse: these, I think, it can be shown, have resulted from a cause analogous to that

Closely resemble in general form and structure atollreefs.Width and depth of the

lagoonchannels.Breaches through the reef in front of valleys, and generally on the leeward

side.Checks to the filling up of the lagoonchannels.Size and constitution of the encircled islands.

Number of islands within the same reef.Barrierreefs of New Caledonia and Australia.Position of the

reef relative to the slope of the adjoining land.Probable great thickness of barrierreefs.

The term "barrier" has been generally applied to that vast reef which fronts the N.E. shore of Australia, and

by most voyagers likewise to that on the western coast of New Caledonia. At one time I thought it convenient

thus to restrict the term, but as these reefs are similar in structure, and in position relatively to the land, to

those, which, like a wall with a deep moat within, encircle many smaller islands, I have classed them

together. The reef, also, on the west coast of New Caledonia, circling round the extremities of the island, is an

intermediate form between a small encircling reef and the Australian barrier, which stretches for a thousand

The geographer Balbi has in effect described those barrierreefs, which encircle moderately sized islands, by

calling them atolls with high land rising from within their central expanse. The general resemblance between

the reefs of the barrier and atoll classes may be seen in the small, but accurately reduced charts on Plate I.

(The authorities from which these charts have been reduced, together with some remarks on them and

descriptive of the Plates, are given separately.), and this resemblance can be further shown to extend to every

part of the structure. Beginning with the outside of the reef; many scattered soundings off Gambier, Oualan,

and some other encircled islands, show that close to the breakers there exists a narrow shelving margin,

beyond which the ocean becomes suddenly unfathomable; but off the west coast of New Caledonia, Captain

Kent (Dalrymple, "Hydrog. Mem." volume iii.) found no bottom with 150 fathoms, at two ships' length from

the reef; so that the slope here must be nearly as precipitous as off the Maldiva atolls.

I can give little information regarding the kinds of corals which live on the outer margin. When I visited the

reef at Tahiti, although it was low water, the surf was too violent for me to see the living masses; but,

according to what I heard from some intelligent native chiefs, they resemble in their rounded and branchless

forms, those on the margin of Keeling atoll. The extreme verge of the reef, which was visible between the

breaking waves at low water, consisted of a rounded, convex, artificiallike breakwater, entirely coated with

Nulliporae, and absolutely similar to that which I have described at Keeling atoll. From what I heard when at

Tahiti, and from the writings of the Revs. W. Ellis and J. Williams, I conclude that this peculiar structure is

common to most of the encircled islands of the Society Archipelago. The reef within this mound or

breakwater, has an extremely irregular surface, even more so than between the islets on the reef of Keeling

atoll, with which alone (as there are no islets on the reef of Tahiti) it can properly be compared. At Tahiti, the

reef is very irregular in width; but round many other encircled islands, for instance, Vanikoro or Gambier

Islands (Figures 1 and 8, Plate I.), it is quite as regular, and of the same average width, as in true atolls. Most

barrierreefs on the inner side slope irregularly into the lagoonchannel (as the space of deep water

separating the reef from the included land may be called), but at Vanikoro the reef slopes only for a short

distance, and then terminates abruptly in a submarine wall, forty feet high,a structure absolutely similar to

In the Society Archipelago, Ellis (Consult, on this and other points, the "Polynesian Researches," by the Rev.

W. Ellis, an admirable work, full of curious information.) states, that the reefs generally lie at the distance of

from one to one and a half miles, and, occasionally, even at more than three miles, from the shore. The

central mountains are generally bordered by a fringe of flat, and often marshy, alluvial land, from one to four

miles in width. This fringe consists of coralsand and detritus thrown up from the lagoonchannel, and of

soil washed down from the hills; it is an encroachment on the channel, analogous to that low and inner part of

the islets in many atolls which is formed by the accumulation of matter from the lagoon. At Hogoleu (Figure

2, Plate I.), in the Caroline Archipelago (See "Hydrographical Mem." and the "Atlas of the Voyage of the

'Astrolabe'," by Captain Dumont D'Urville, page 428.), the reef on the south side is no less than twenty miles;

on the east side, five; and on the north side, fourteen miles from the encircled high islands.

The lagoon channels may be compared in every respect with true lagoons. In some cases they are open, with

a level bottom of fine sand; in others they are choked up with reefs of delicately branched corals, which have

the same general character as those within the Keeling atoll. These internal reefs either stand separately, or

more commonly skirt the shores of the included high islands. The depth of the lagoonchannel round the

Society Islands varies from two or three to thirty fathoms; in Cook's (See the chart in volume i. of

Hawkesworth's 4to edition of "Cook's First Voyage.") chart of Ulieta, however, there is one sounding laid

down of fortyeight fathoms; at Vanikoro there are several of fiftyfour and one of fiftysix and a half

fathoms (English), a depth which even exceeds by a little that of the interior of the great Maldiva atolls. Some

barrierreefs have very few islets on them; whilst others are surmounted by numerous ones; and those round

part of Bolabola (Plate I., Figure 5) form a single linear strip. The islets first appear either on the angles of the

reef, or on the sides of the breaches through it, and are generally most numerous on the windward side. The

reef to leeward retaining its usual width, sometimes lies submerged several fathoms beneath the surface; I

have already mentioned Gambier Island as an instance of this structure. Submerged reefs, having a less

defined outline, dead, and covered with sand, have been observed (see Appendix) off some parts of Huaheine

and Tahiti. The reef is more frequently breached to leeward than to windward; thus I find in Krusenstern's

"Memoir on the Pacific," that there are passages through the encircling reef on the leeward side of each of the

seven Society Islands, which possess shipharbours; but that there are openings to windward through the reef

of only three of them. The breaches in the reef are seldom as deep as the interior lagoonlike channel; they

generally occur in front of the main valleys, a circumstance which can be accounted for, as will be seen in the

fourth chapter, without much difficulty. The breaches being situated in front of the valleys, which descend

indifferently on all sides, explains their more frequent occurrence through the windward side of barrierreefs

than through the windward side of atolls,for in atolls there is no included land to influence the position of

It is remarkable, that the lagoonchannels round mountainous islands have not in every instance been long

ago filled up with coral and sediment; but it is more easily accounted for than appears at first sight. In cases

like that of Hogoleu and the Gambier Islands, where a few small peaks rise out of a great lagoon, the

conditions scarcely differ from those of an atoll, and I have already shown, at some length, that the filling up

of a true lagoon must be an extremely slow process. Where the channel is narrow, the agency, which on

unprotected coasts is most productive of sediment, namely the force of the breakers, is here entirely excluded,

and the reef being breached in the front of the main valleys, much of the finer mud from the rivers must be

transported into the open sea. As a current is formed by the water thrown over the edge of atollformed reefs,

which carries sediment with it through the deepwater breaches, the same thing probably takes place in

barrierreefs, and this would greatly aid in preventing the lagoonchannel from being filled up. The low

alluvial border, however, at the foot of the encircled mountains, shows that the work of filling up is in

progress; and at Maura (Plate I., Figure 6), in the Society group, it has been almost effected, so that there

If we look at a set of charts of barrierreefs, and leave out in imagination the encircled land, we shall find

that, besides the many points already noticed of resemblance, or rather of identity in structure with atolls,

there is a close general agreement in form, average dimensions, and grouping. Encircling barrierreefs, like

atolls, are generally elongated, with an irregularly rounded, though sometimes angular outline. There are

atolls of all sizes, from less than two miles in diameter to sixty miles (excluding TilladouMatte, as it

consists of a number of almost independent atollformed reefs); and there are encircling barrierreefs from

three miles and a half to fortysix miles in diameter,Turtle Island being an instance of the former, and

Hogoleu of the latter. At Tahiti the encircled island is thirtysix miles in its longest axis, whilst at Maurua it

is only a little more than two miles. It will be shown, in the last chapter in this volume, that there is the

strictest resemblance in the grouping of atolls and of common islands, and consequently there must be the

The islands lying within reefs of this class, are of very various heights. Tahiti is 7,000 feet (The height of

Tahiti is given from Captain Beechey; Maurua from Mr. F.D. Bennett ("Geograph. Journ." volume viii., page

220); Aitutaki from measurements made on board the "Beagle"; and Manouai or Harvey Island, from an

estimate by the Rev. J. Williams. The two latter islands, however, are not in some respects well characterised

examples of the encircled class.); Maurua about 800; Aitutaki 360, and Manouai only 50. The geological

nature of the included land varies: in most cases it is of ancient volcanic origin, owing apparently to the fact

that islands of this nature are most frequent within all great seas; some, however, are of madreporitic

limestone, and others of primary formation, of which latter kind New Caledonia offers the best example. The

central land consists either of one island, or of several: thus, in the Society group, Eimeo stands by itself;

while Taha and Raiatea (Figure 3, Plate I.), both moderately large islands of nearly equal size, are included in

one reef. Within the reef of the Gambier group there are four large and some smaller islands (Figure 8, Plate

I.); within that of Hogoleu (Figure 2, Plate I.) nearly a dozen small islands are scattered over the expanse of

After the details now given, it may be asserted that there is not one point of essential difference between

encircling barrierreefs and atolls: the latter enclose a simple sheet of water, the former encircle an expanse

with one or more islands rising from it. I was much struck with this fact, when viewing, from the heights of

Tahiti, the distant island of Eimeo standing within smooth water, and encircled by a ring of snowwhite

breakers. Remove the central land, and an annular reef like that of an atoll in an early stage of its formation is

left; remove it from Bolabola, and there remains a circle of linear coralislets, crowned with tall cocoanut

trees, like one of the many atolls scattered over the Pacific and Indian Oceans.

The barrierreefs of Australia and of New Caledonia deserve a separate notice from their great dimensions.

The reef on the west coast of New Caledonia (Figure 5, Plate II.) is 400 miles in length; and for a length of

many leagues it seldom approaches within eight miles of the shore; and near the southern end of the island,

the space between the reef and the land is sixteen miles in width. The Australian barrier extends, with a few

interruptions, for nearly a thousand miles; its average distance from the land is between twenty and thirty

miles; and in some parts from fifty to seventy. The great arm of the sea thus included, is from ten to

twentyfive fathoms deep, with a sandy bottom; but towards the southern end, where the reef is further from

the shore, the depth gradually increases to forty, and in some parts to more than sixty fathoms. Flinders

(Flinders' "Voyage to Terra Australis," volume ii., page 88.) has described the surface of this reef as

consisting of a hard white agglomerate of different kinds of coral, with rough projecting points. The outer

edge is the highest part; it is traversed by narrow gullies, and at rare intervals is breached by shipchannels.

The sea close outside is profoundly deep; but, in front of the main breaches, soundings can sometimes be

1. VANIKORO, from the "Atlas of the Voyage of the 'Astrolabe'," by D. D'Urville.

The horizontal line is the level of the sea, from which on the right hand a plummet descends, representing a

depth of 200 fathoms, or 1,200 feet. The vertical shading shows the section of the land, and the horizontal

shading that of the encircling barrierreef: from the smallness of the scale, the lagoonchannel could not be

There is one important point in the structure of barrierreefs which must here be considered. The

accompanying diagrams represent north and south vertical sections, taken through the highest points of

Vanikoro, Gambier, and Maurua Islands, and through their encircling reefs. The scale both in the horizontal

and vertical direction is the same, namely, a quarter of an inch to a nautical mile. The height and width of

these islands is known; and I have attempted to represent the form of the land from the shading of the hills in

the large published charts. It has long been remarked, even from the time of Dampier, that considerable

degree of relation subsists between the inclination of that part of the land which is beneath water and that

above it; hence the dotted line in the three sections, probably, does not widely differ in inclination from the

actual submarine prolongation of the land. If we now look at the outer edge of the reef (AA), and bear in

mind that the plummet on the right hand represents a depth of 1,200 feet, we must conclude that the vertical

I must observe that if the sections had been taken in any other direction across these islands, or across other

encircled islands (In the fifth chapter an east and west section across the Island of Bolabola and its

barrierreefs is given, for the sake of illustrating another point. The unbroken line in it (woodcut No. 5) is the

section referred to. The scale is .57 of an inch to a mile; it is taken from the "Atlas of the Voyage of the

'Coquille'," by Duperrey. The depth of the lagoonchannel is exaggerated.), the result would have been the

same. In the succeeding chapter it will be shown that reefbuilding polypifers cannot flourish at great

depths,for instance, it is highly improbable that they could exist at a quarter of the depth represented by the

plummet on the right hand of the woodcut. Here there is a great APPARENT difficultyhow were the basal

parts of these barrierreef formed? It will, perhaps, occur to some, that the actual reefs formed of coral are

not of great thickness, but that before their first growth, the coasts of these encircled islands were deeply

eaten into, and a broad but shallow submarine ledge thus left, on the edge of which the coral grew; but if this

had been the case, the shore would have been invariably bounded by lofty cliffs, and not have sloped down to

the lagoonchannel, as it does in many instances. On this view (The Rev. D. Tyerman and Mr. Bennett

("Journal of Voyage and Travels," volume i., page 215) have briefly suggested this explanation of the origin

of the encircling reefs of the Society Islands.), moreover, the cause of the reef springing up at such a great

distance from the land, leaving a deep and broad moat within, remains altogether unexplained. A supposition

of the same nature, and appearing at first more probable is, that the reefs sprung up from banks of sediment,

which had accumulated round the shore previously to the growth of the coral; but the extension of a bank to

the same distance round an unbroken coast, and in front of those deep arms of the sea (as in Raiatea, see Plate

II., Figure 3) which penetrate nearly to the heart of some encircled islands, is exceedingly improbable. And

why, again, should the reef spring up, in some cases steep on both sides like a wall, at a distance of two, three

or more miles from the shore, leaving a channel often between two hundred and three hundred feet deep, and

rising from a depth which we have reason to believe is destructive to the growth of coral? An admission of

this nature cannot possibly be made. The existence, also, of the deep channel, utterly precludes the idea of the

reef having grown outwards, on a foundation slowly formed on its outside, by the accumulation of sediment

and coral detritus. Nor, again, can it be asserted, that the reefbuilding corals will not grow, excepting at a

great distance from the land; for, as we shall soon see, there is a whole class of reefs, which take their name

from growing closely attached (especially where the sea is deep) to the beach. At New Caledonia (see Plate

II., Figure 5) the reefs which run in front of the west coast are prolonged in the same line 150 miles beyond

the northern extremity of the island, and this shows that some explanation, quite different from any of those

just suggested, is required. The continuation of the reefs on each side of the submarine prolongation of New

Caledonia, is an exceedingly interesting fact, if this part formerly existed as the northern extremity of the

island, and before the attachment of the coral had been worn down by the action of the sea, or if it originally

existed at its present height, with or without beds of sediment on each flank, how can we possibly account for

the reefs, not growing on the crest of this submarine portion, but fronting its sides, in the same line with the

reefs which front the shores of the lofty island? We shall hereafter see, that there is one, and I believe only

One other supposition to account for the position of encircling barrierreefs remains, but it is almost too

preposterous to be mentioned; namely, that they rest on enormous submarine craters, surrounding the

included islands. When the size, height, and form of the islands in the Society group are considered, together

with the fact that all are thus encircled, such a notion will be rejected by almost every one. New Caledonia,

moreover, besides its size, is composed of primitive formations, as are some of the Comoro Islands (I have

been informed that this is the case by Dr. Allan of Forres, who has visited this group.); and Aitutaki consists

of calcareous rock. We must, therefore, reject these several explanations, and conclude that the vertical

thickness of barrierreefs, from their outer edges to the foundation on which they rest (from AA in the

section to the dotted lines) is really great; but in this, there is no difficulty, for it is not necessary to suppose

that the coral has sprung up from an immense depth, as will be evident when the theory of the upward growth

Reefs of Mauritius.Shallow channel within the reef.Its slow filling up.Currents of water formed

within it.Upraised reefs.Narrow fringingreefs in deep seas.Reefs on the coast of East Africa and of

Brazil.Fringingreefs in very shallow seas, round banks of sediment and on worndown

islands.Fringingreefs affected by currents of the sea. Coral coating the bottom of the sea, but not

Fringingreefs, or, as they have been called by some voyagers, shorereefs, whether skirting an island or part

of a continent, might at first be thought to differ little, except in generally being of less breadth, from

barrierreefs. As far as the superficies of the actual reef is concerned this is the case; but the absence of an

interior deepwater channel, and the close relation in their horizontal extension with the probable slope

The reefs which fringe the island of Mauritius offer a good example of this class. They extend round its

whole circumference, with the exception of two or three parts (This fact is stated on the authority of the

Officier du Roi, in his extremely interesting "Voyage a l'Isle de France," undertaken in 1768. According to

Captain Carmichael (Hooker's "Bot. Misc." volume ii., page 316) on one part of the coast there is a space for

sixteen miles without a reef.), where the coast is almost precipitous, and where, if as is probable the bottom of

the sea has a similar inclination, the coral would have no foundation on which to become attached. A similar

fact may sometimes be observed even in reefs of the barrier class, which follow much less closely the outline

of the adjoining land; as, for instance, on the southeast and precipitous side of Tahiti, where the encircling

reef is interrupted. On the western side of the Mauritius, which was the only part I visited, the reef generally

lies at the distance of about half a mile from the shore; but in some parts it is distant from one to two, and

even three miles. But even in this last case, as the coastland is gently inclined from the foot of the mountains

to the seabeach, and as the soundings outside the reef indicate an equally gentle slope beneath the water,

there is no reason for supposing that the basis of the reef, formed by the prolongation of the strata of the

island, lies at a greater depth than that at which the polypifers could begin constructing the reef. Some

allowance, however, must be made for the outward extension of the corals on a foundation of sand and

detritus, formed from their own wear, which would give to the reef a somewhat greater vertical thickness,

The outer edge of the reef on the western or leeward side of the island is tolerably well defined, and is a little

higher than any other part. It chiefly consists of large strongly branched corals, of the genus Madrepora,

which also form a sloping bed some way out to sea: the kinds of coral growing in this part will be described

in the ensuing chapter. Between the outer margin and the beach, there is a flat space with a sandy bottom and

a few tufts of living coral; in some parts it is so shallow, that people, by avoiding the deeper holes and gullies,

can wade across it at low water; in other parts it is deeper, seldom however exceeding ten or twelve feet, so

that it offers a safe coasting channel for boats. On the eastern and windward side of the island, which is

exposed to a heavy surf, the reef was described to me as having a hard smooth surface, very slightly inclined

inwards, just covered at lowwater, and traversed by gullies; it appears to be quite similar in structure to the

The reef of Mauritius, in front of every river and streamlet, is breached by a straight passage: at Grand Port,

however, there is a channel like that within a barrierreef; it extends parallel to the shore for four miles, and

has an average depth of ten or twelve fathoms; its presence may probably be accounted for by two rivers

which enter at each end of the channel, and bend towards each other. The fact of reefs of the fringing class

being always breached in front of streams, even of those which are dry during the greater part of the year,

will be explained, when the conditions unfavourable to the growth of coral are considered. Low coralislets,

like those on barrierreefs and atolls, are seldom formed on reefs of this class, owing apparently in some

cases to their narrowness, and in others to the gentle slope of the reef outside not yielding many fragments to

the breakers. On the windward side, however, of the Mauritius, two or three small islets have been formed.

It appears, as will be shown in the ensuing chapter, that the action of the surf is favourable to the vigorous

growth of the stronger corals, and that sand or sediment, if agitated by the waves, is injurious to them. Hence

it is probable that a reef on a shelving shore, like that of Mauritius, would at first grow up, not attached to the

actual beach, but at some little distance from it; and the corals on the outer margin would be the most

vigorous. A shallow channel would thus be formed within the reef, and as the breakers are prevented acting

on the shores of the island, and as they do not ordinarily tear up many fragments from the outside, and as

every streamlet has its bed prolonged in a straight line through the reef, this channel could be filled up only

very slowly with sediment. But a beach of sand and of fragments of the smaller kinds of coral seems, in the

case of Mauritius, to be slowly encroaching on the shallow channel. On many shelving and sandy coasts, the

breakers tend to form a bar of sand a little way from the beach, with a slight increase of depth within it; for

instance, Captain Grey (Captain Grey's "Journal of Two Expeditions," volume i. page 369.) states that the

west coast of Australia, in latitude 24 deg., is fronted by a sand bar about two hundred yards in width, on

which there is only two feet of water; but within it the depth increases to two fathoms. Similar bars, more or

less perfect, occur on other coasts. In these cases I suspect that the shallow channel (which no doubt during

storms is occasionally obliterated) is scooped out by the flowing away of the water thrown beyond the line,

on which the waves break with the greatest force. At Pernambuco a bar of hard sandstone (I have described

this singular structure in the "London and Edinburgh Phil. Mag." October 1841.), which has the same

external form and height as a coralreef, extends nearly parallel to the coast; within this bar currents,

apparently caused by the water thrown over it during the greater part of each tide, run strongly, and are

wearing away its inner wall. From these facts it can hardly be doubted, that within most fringingreefs,

especially within those lying some distance from the land, a return stream must carry away the water thrown

over the outer edge; and the current thus produced, would tend to prevent the channel being filled up with

sediment, and might even deepen it under certain circumstances. To this latter belief I am led, by finding that

channels are almost universally present within the fringingreefs of those islands which have undergone

recent elevatory movements; and this could hardly have been the case, if the conversion of the very shallow

A fringingreef, if elevated in a perfect condition above the level of the sea, ought to present the singular

appearance of a broad dry moat within a low mound. The author ("Voyage a l'Isle de France, par un Officier

du Roi," part i., pages 192, 200.) of an interesting pedestrian tour round the Mauritius, seems to have met

with a structure of this kind: he says "J'observai que la, ou la mer etale, independamment des rescifs du large,

il y a terre UNE ESPECE D'EFFONCEMENT ou chemin couvert naturel. On y pourrait mettre du canon,"

etc. In another place he adds, "Avant de passer le Cap, on remarque un gros banc de corail eleve de plus de

quinze pieds: c'est une espece de rescif, que la mer abandonne, il regne au pied une longue flaque d'eau, dont

on pourrait faire un bassin pour de petits vaisseaux." But the margin of the reef, although the highest and

most perfect part, from being most exposed to the surf, would generally during a slow rise of the land be

either partially or entirely worn down to that level, at which corals could renew their growth on its upper

edge. On some parts of the coastland of Mauritius there are little hillocks of coralrock, which are either the

last remnants of a continuous reef, or of low islets formed on it. I observed that two such hillocks between

Tamarin Bay and the Great Black River; they were nearly twenty feet high, about two hundred yards from the

present beach, and about thirty feet above its level. They rose abruptly from a smooth surface, strewed with

worn fragments of coral. They consisted in their lower part of hard calcareous sandstone, and in their upper

of great blocks of several species of Astraea and Madrepora, loosely aggregated; they were divided into

irregular beds, dipping seaward, in one hillock at an angle of 8 deg., and in the other at 18 deg. I suspect that

the superficial parts of the reefs, which have been upraised together with the islands they fringe, have

generally been much more modified by the wearing action of the sea, than those of Mauritius.

Many islands are fringed by reefs quite similar to those of Mauritius (I may give Cuba, as another instance;

Mr. Taylor ("Loudon's Mag. of Nat. Hist." volume ix., page 449) has described a reef several miles in length

between Gibara and Vjaro, which extends parallel to the shore at the distance of between half and the third

part of a mile, and encloses a space of shallow water, with a sandy bottom and tufts of coral. Outside the edge

of the reef, which is formed of great branching corals, the depth is six and seven fathoms. This coast has been

upheaved at no very distant geological period."); but on coasts where the sea deepens very suddenly the reefs

are much narrower, and their limited extension seems evidently to depend on the high inclination of the

submarine slope; a relation, which, as we have seen, does not exist in reefs of the barrier class. The

fringingreefs on steep coasts are frequently not more than from fifty to one hundred yards in width; they

have a nearly smooth, hard surface, scarcely uncovered at low water, and without any interior shoal channel,

like that within those fringingreefs, which lie at a greater distance from the land. The fragments torn up

during gales from the outer margin are thrown over the reef on the shores of the island. I may give as

instances, Wateeo, where the reef is described by Cook as being a hundred yards wide; and Mauti and

Elizabeth Islands (Mauti is described by Lord Byron in the voyage of H.M.S. "Blonde", and Elizabeth Island

by Captain Beechey.), where it is only fifty yards in width: the sea round these islands is very deep.

Fringingreefs, like barrierreefs, both surround islands, and front the shores of continents. In the charts of

the eastern coast of Africa, by Captain Owen, many extensive fringingreefs are laid down; thus, for a space

of nearly forty miles, from latitude 1 deg 15' to 1 deg 45' S., a reef fringes the shore at an average distance of

rather more than one mile, and therefore at a greater distance than is usual in reefs of this class; but as the

coastland is not lofty, and as the bottom shoals very gradually (the depth being only from eight to fourteen

fathoms at a mile and a half outside the reef), its extension thus far from the land offers no difficulty. The

external margin of this reef is described, as formed of projecting points, within which there is a space, from

six to twelve feet deep, with patches of living coral on it. At Mukdeesha (latitude 2 deg 1' N.) "the port is

formed," it is said (Owen's "Africa," volume i., page 357, from which work the foregoing facts are likewise

taken.) "by a long reef extending eastward, four or five miles, within which there is a narrow channel, with

ten to twelve feet of water at low springtides;" it lies at the distance of a quarter of a mile from the shore.

Again, in the plan of Mombas (latitude 4 deg S.), a reef extends for thirtysix miles, at the distance of from

half a mile to one mile and a quarter from the shore; within it, there is a channel navigable "for canoes and

small craft," between six and fifteen feet deep: outside the reef the depth is about thirty fathoms at the

distance of nearly half a mile. Part of this reef is very symmetrical, and has a uniform breadth of two hundred

The coast of Brazil is in many parts fringed by reefs. Of these, some are not of coral formation; for instance,

those near Bahia and in front of Pernambuco; but a few miles south of this latter city, the reef follows (See

Baron Roussin's "Pilote du Bresil," and accompanying hydrographical memoir.) so closely every turn of the

shore, that I can hardly doubt it is of coral; it runs at the distance of threequarters of a mile from the land,

and within it the depth is from ten to fifteen feet. I was assured by an intelligent pilot that at Ports Frances

and Maceio, the outer part of the reef consists of living coral, and the inner of a white stone, full of large

irregular cavities, communicating with the sea. The bottom of the sea off the coast of Brazil shoals gradually

to between thirty and forty fathoms, at the distance of between nine and ten leagues from the land.

From the description now given, we must conclude that the dimensions and structure of fringingreefs

depend entirely on the greater or less inclination of the submarine slope, conjoined with the fact that

reefbuilding polypifers can exist only at limited depths. It follows from this, that where the sea is very

shallow, as in the Persian Gulf and in parts of the East Indian Archipelago, the reefs lose their fringing

character, and appear as separate and irregularly scattered patches, often of considerable area. From the more

vigorous growth of the coral on the outside, and from the conditions being less favourable in several respects

within, such reefs are generally higher and more perfect in their marginal than in their central parts; hence

these reefs sometimes assume (and this circumstance ought not to be overlooked) the appearance of atolls;

but they differ from atolls in their central expanse being much less deep, in their form being less defined, and

in being based on a shallow foundation. But when in a deep sea reefs fringe banks of sediment, which have

accumulated beneath the surface, round either islands or submerged rocks, they are distinguished with

difficulty on the one hand from encircling barrierreefs, and on the other from atolls. In the West Indies there

are reefs, which I should probably have arranged under both these classes, had not the existence of large and

level banks, lying a little beneath the surface, ready to serve as the basis for the attachment of coral, been

occasionally brought into view by the entire or partial absence of reefs on them, and had not the formation of

such banks, through the accumulation of sediment now in progress, been sufficiently evident. Fringingreefs

sometimes coat, and thus protect the foundations of islands, which have been worn down by the surf to the

level of the sea. According to Ehrenberg, this has been extensively the case with the islands in the Red Sea,

which formerly ranged parallel to the shores of the mainland, with deep water within them: hence the reefs

now coating their bases are situated relatively to the land like barrierreefs, although not belonging to that

class; but there are, as I believe, in the Red Sea some true barrierreefs. The reefs of this sea and of the West

Indies will be described in the Appendix. In some cases, fringingreefs appear to be considerably modified in

outline by the course of the prevailing currents. Dr. J. Allan informs me that on the east coast of Madagascar

almost every headland and low point of sand has a coralreef extending from it in a S.W. and N.E. line,

parallel to the currents on that shore. I should think the influence of the currents chiefly consisted in causing

an extension, in a certain direction, of a proper foundation for the attachment of the coral. Round many

intertropical islands, for instance the Abrolhos on the coast of Brazil surveyed by Captain Fitzroy, and, as I

am informed by Mr. Cuming, round the Philippines, the bottom of the sea is entirely coated by irregular

masses of coral, which although often of large size, do not reach the surface and form proper reefs. This must

be owing, either to insufficient growth, or to the absence of those kinds of corals which can withstand the

The three classes, atollformed, barrier, and fringingreefs, together with the modifications just described of

the latter, include all the most remarkable coral formations anywhere existing. At the commencement of the

last chapter in the volume, where I detail the principles on which the map (Plate III.) is coloured, the

In this chapter I will give all the facts which I have collected, relating to the distribution of coralreefs,to

the conditions favourable to their increase,to the rate of their growth,and to the depth at which they are

These subjects have an important bearing on the theory of the origin of the different classes of coralreefs.

With regard to the limits of latitude, over which coralreefs extend, I have nothing new to add. The Bermuda

Islands, in 32 deg 15' N., is the point furthest removed from the equator, in which they appear to exist; and it

has been suggested that their extension so far northward in this instance is owing to the warmth of the Gulf

Stream. In the Pacific, the Loo Choo Islands, in latitude 27 deg N., have reefs on their shores, and there is an

atoll in 28 deg 30', situated N.W. of the Sandwich Archipelago. In the Red Sea there are coralreefs in

latitude 30 deg. In the southern hemisphere coralreefs do not extend so far from the equatorial sea. In the

Southern Pacific there are only a few reefs beyond the line of the tropics, but Houtmans Abrolhos, on the

The proximity of volcanic land, owing to the lime generally evolved from it, has been thought to be

favourable to the increase of coralreefs. There is, however, not much foundation for this view; for nowhere

are coralreefs more extensive than on the shores of New Caledonia, and of northeastern Australia, which

consist of primary formations; and in the largest groups of atolls, namely the Maldiva, Chagos, Marshall,

Gilbert, and Low Archipelagoes, there is no volcanic or other kind of rock, excepting that formed of coral.

The entire absence of coralreefs in certain large areas within the tropical seas, is a remarkable fact. Thus no

coralreefs were observed, during the surveying voyages of the "Beagle" and her tender on the west coast of

South America south of the equator, or round the Galapagos Islands. It appears, also, that there are none (I

have been informed that this is the case, by Lieutenant Ryder, R.N., and others who have had ample

opportunities for observation.) north of the equator; Mr. Lloyd, who surveyed the Isthmus of Panama,

remarked to me, that although he had seen corals living in the Bay of Panama, yet he had never observed any

reefs formed by them. I at first attributed this absence of reefs on the coasts of Peru and of the Galapagos

Islands (The mean temperature of the surface sea from observations made by the direction of Captain Fitzroy

on the shores of the Galapagos Islands, between the 16th of September and the 20th of October, 1835, was 68

deg Fahr. The lowest temperature observed was 58.5 deg at the southwest end of Albemarle Island; and on

the west coast of this island, it was several times 62 deg and 63 deg. The mean temperature of the sea in the

Low Archipelago of atolls, and near Tahiti, from similar observations made on board the "Beagle", was

(although further from the equator) 77.5 deg, the lowest any day being 76.5 deg. Therefore we have here a

difference of 9.5 deg in mean temperature, and 18 deg in extremes; a difference doubtless quite sufficient to

affect the distribution of organic beings in the two areas.), to the coldness of the currents from the south, but

the Gulf of Panama is one of the hottest pelagic districts in the world. (Humboldt's "Personal Narrative,"

volume vii., page 434.) In the central parts of the Pacific there are islands entirely free from reefs; in some

few of these cases I have thought that this was owing to recent volcanic action; but the existence of reefs

round the greater part of Hawaii, one of the Sandwich Islands, shows that recent volcanic action does not

In the last chapter I stated that the bottom of the sea round some islands is thickly coated with living corals,

which nevertheless do not form reefs, either from insufficient growth, or from the species not being adapted

I have been assured by several people, that there are no coralreefs on the west coast of Africa (It might be

concluded, from a paper by Captain Owen ("Geographical Journal", volume ii., page 89), that the reefs off

Cape St. Anne and the Sherboro' Islands were of coral, although the author states that they are not purely

coralline. But I have been assured by Lieutenant Holland, R.N., that these reefs are not of coral, or at least

that they do not at all resemble those in the West Indies.), or round the islands in the Gulf of Guinea. This

perhaps may be attributed, in part, to the sediment brought down by the many rivers debouching on that

coast, and to the extensive mudbanks, which line great part of it. But the islands of St. Helena, Ascension,

the Cape Verdes, St. Paul's, and Fernando Noronha, are, also, entirely without reefs, although they lie far out

at sea, are composed of the same ancient volcanic rocks, and have the same general form, with those islands

in the Pacific, the shores of which are surrounded by gigantic walls of coralrock. With the exception of

Bermuda, there is not a single coralreef in the central expanse of the Atlantic Ocean. It will, perhaps, be

suggested that the quantity of carbonate of lime in different parts of the sea, may regulate the presence of

reefs. But this cannot be the case, for at Ascension, the waves charged to excess precipitate a thick layer of

calcareous matter on the tidal rocks; and at St. Jago, in the Cape Verdes, carbonate of lime not only is

abundant on the shores, but it forms the chief part of some upraised posttertiary strata. The apparently

capricious distribution, therefore, of coralreefs, cannot be explained by any of these obvious causes; but as

the study of the terrestrial and better known half of the world must convince every one that no station capable

of supporting life is lost,nay more, that there is a struggle for each station, between the different orders of

nature,we may conclude that in those parts of the intertropical sea, in which there are no coralreefs, there

are other organic bodies supplying the place of the reefbuilding polypifers. It has been shown in the chapter

on Keeling atoll that there are some species of large fish, and the whole tribe of Holothuriae which prey on

the tenderer parts of the corals. On the other hand, the polypifers in their turn must prey on some other

organic beings; the decrease of which from any cause would cause a proportionate destruction of the living

coral. The relations, therefore, which determine the formation of reefs on any shore, by the vigorous growth

of the efficient kinds of coral, must be very complex, and with our imperfect knowledge quite inexplicable.

From these considerations, we may infer that changes in the condition of the sea, not obvious to our senses,

might destroy all the coralreefs in one area, and cause them to appear in another: thus, the Pacific or Indian

Ocean might become as barren of coralreefs as the Atlantic now is, without our being able to assign any

It has been a question with some naturalists, which part of a reef is most favourable to the growth of coral.

The great mounds of living Porites and of Millepora round Keeling atoll occur exclusively on the extreme

verge of the reef, which is washed by a constant succession of breakers; and living coral nowhere else forms

solid masses. At the Marshall islands the larger kinds of coral (chiefly species of Astraea, a genus closely

allied to Porites) "which form rocks measuring several fathoms in thickness," prefer, according to Chamisso

(Kotzebue's "First Voyage" (English Translation), volume iii., pages 142, 143, 331.), the most violent surf. I

have stated that the outer margin of the Maldiva atolls consists of living corals (some of which, if not all, are

of the same species with those at Keeling atoll), and here the surf is so tremendous, that even large ships have

been thrown, by a single heave of the sea, high and dry on the reef, all on board thus escaping with their lives.

Ehrenberg (Ehrenberg, "Uber die Natur und Bildung der Corallen Banke im rothen Meere," page 49.)

remarks, that in the Red Sea the strongest corals live on the outer reefs, and appear to love the surf; he adds,

that the more branched kinds abound a little way within, but that even these in still more protected places,

become smaller. Many other facts having a similar tendency might be adduced. (In the West Indies, as I am

informed by Captain Bird Allen, R.N., it is the common belief of those, who are best acquainted with the

reefs, that the coral flourishes most, where freely exposed to the swell of the open sea.) It has, however, been

doubted by MM. Quoy and Gaimard, whether any kind of coral can even withstand, much less flourish in, the

breakers of an open sea ("Annales des Sciences Naturelles," tome vi., pages 276, 278."La ou les ondes sont

agitees, les Lytophytes ne peuvent travailler, parce qu'elles detruiraient leurs fragiles edifices," etc.): they

affirm that the saxigenous lithophytes flourish only where the water is tranquil, and the heat intense. This

statement has passed from one geological work to another; nevertheless, the protection of the whole reef

undoubtedly is due to those kinds of coral, which cannot exist in the situations thought by these naturalists to

be most favourable to them. For should the outer and living margin perish, of any one of the many low

coralislands, round which a line of great breakers is incessantly foaming, the whole, it is scarcely possible to

doubt, would be washed away and destroyed, in less than half a century. But the vital energies of the corals

conquer the mechanical power of the waves; and the large fragments of reef torn up by every storm, are

replaced by the slow but steady growth of the innumerable polypifers, which form the living zone on its outer

From these facts, it is certain, that the strongest and most massive corals flourish, where most exposed. The

less perfect state of the reef of most atolls on the leeward and less exposed side, compared with its state to

windward; and the analogous case of the greater number of breaches on the near sides of those atolls in the

Maldiva Archipelago, which afford some protection to each other, are obviously explained by this

circumstance. If the question had been, under what conditions the greater number of species of coral, not

regarding their bulk and strength, were developed, I should answer,probably in the situations described by

MM. Quoy and Gaimard, where the water is tranquil and the heat intense. The total number of species of

coral in the circumtropical seas must be very great: in the Red Sea alone, 120 kinds, according to Ehrenberg

The same author has observed that the recoil of the sea from a steep shore is injurious to the growth of coral,

although waves breaking over a bank are not so. Ehrenberg also states, that where there is much sediment,

placed so as to be liable to be moved by the waves there is little or no coral; and a collection of living

specimens placed by him on a sandy shore died in the course of a few days. (Ibid., page 49.) An experiment,

however, will presently be related in which some large masses of living coral increased rapidly in size, after

having been secured by stakes on a sandbank. That loose sediment should be injurious to the living

polypifers, appears, at first sight, probable; and accordingly, in sounding off Keeling atoll, and (as will

hereafter be shown) off Mauritius, the arming of the lead invariably came up clean, where the coral was

growing vigorously. This same circumstance has probably given rise to a strange belief, which, according to

Captain Owen (Captain Owen on the Geography of the Maldiva Islands, "Geographical Journal", volume ii.,

page 88.), is general amongst the inhabitants of the Maldiva atolls, namely that corals have roots, and

therefore that if merely broken down to the surface, they grow up again; but, if rooted out, they are

permanently destroyed. By this means the inhabitants keep their harbours clear; and thus the French

Governor of St. Mary's in Madagascar, "cleared out and made a beautiful little port at that place." For it is

probable that sand would accumulate in the hollows formed by tearing out the corals, but not on the broken

and projecting stumps, and therefore, in the former case, the fresh growth of the coral might be thus

In the last chapter I remarked that fringingreefs are almost universally breached, where streams enter the

sea. (Lieutenant Wellstead and others have remarked that this is the case in the Red Sea; Dr. Ruppell ("Reise

in Abyss." Band. i., page 142) says that there are pearshaped harbours in the upraised coralcoast, into

which periodical streams enter. From this circumstance, I presume, we must infer that before the upheaval of

the strata now forming the coastland, fresh water and sediment entered the sea at these points; and the coral

being thus prevented growing, the pearshaped harbours were produced.) Most authors have attributed this

fact to the injurious effects of the fresh water, even where it enters the sea only in small quantity, and during a

part of the year. No doubt brackish water would prevent or retard the growth of coral; but I believe that the

mud and sand which is deposited, even by rivulets when flooded, is a much more efficient check. The reef on

each side of the channel leading into Port Louis at Mauritius, ends abruptly in a wall, at the foot of which I

sounded and found a bed of thick mud. This steepness of the sides appears to be a general character in such

breaches. Cook (Cook's "First Voyage," volume ii., page 271 (Hawkesworth's edition).), speaking of one at

Raiatea, says, "like all the rest, it is very steep on both sides." Now, if it were the fresh water mingling with

the salt which prevented the growth of coral, the reef certainly would not terminate abruptly, but as the

polypifers nearest the impure stream would grow less vigorously than those farther off, so would the reef

gradually thin away. On the other hand, the sediment brought down from the land would only prevent the

growth of the coral in the line of its deposition, but would not check it on the side, so that the reefs might

increase till they overhung the bed of the channel. The breaches are much fewer in number, and front only the

larger valleys in reefs of the encircling barrier class. They probably are kept open in the same manner as

those into the lagoon of an atoll, namely, by the force of the currents and the drifting outwards of fine

sediment. Their position in front of valleys, although often separated from the land by deep water

lagoonchannels, which it might be thought would entirely remove the injurious effects both of the fresh

water and the sediment, will receive a simple explanation when we discuss the origin of barrierreefs.

In the vegetable kingdom every different station has its peculiar group of plants, and similar relations appear

to prevail with corals. We have already described the great difference between the corals within the lagoon of

an atoll and those on its outer margin. The corals, also, on the margin of Keeling Island occurred in zones;

thus the Porites and Millepora complanata grow to a large size only where they are washed by a heavy sea,

and are killed by a short exposure to the air; whereas, three species of Nullipora also live amidst the breakers,

but are able to survive uncovered for a part of each tide; at greater depths, a strong Madrepora and Millepora

alcicornis are the commonest kinds, the former appearing to be confined to this part, beneath the zone of

massive corals, minute encrusting corallines and other organic bodies live. If we compare the external margin

of the reef at Keeling atoll with that on the leeward side of Mauritius, which are very differently

circumstanced, we shall find a corresponding difference in the appearance of the corals. At the latter place,

the genus Madrepora is preponderant over every other kind, and beneath the zone of massive corals there are

large beds of Seriatopora. There is also a marked difference, according to Captain Moresby (Captain Moresby

on the Northern Maldiva atolls, "Geographical Journal", volume v., page 401.), between the great branching

These facts, which in themselves are deserving of notice, bear, perhaps, not very remotely, on a remarkable

circumstance which has been pointed out to me by Captain Moresby, namely, that with very few exceptions,

none of the coralknolls within the lagoons of Peros Banhos, Diego Garcia, and the Great Chagos Bank (all

situated in the Chagos group), rise to the surface of the water; whereas all those, with equally few exceptions,

within Solomon and Egmont atolls in the same group, and likewise within the large southern Maldiva atolls,

reach the surface. I make these statements, after having examined the charts of each atoll. In the lagoon of

Peros Banhos, which is nearly twenty miles across, there is only one single reef which rises to the surface; in

Diego Garcia there are seven, but several of these lie close to the margin of the lagoon, and need scarcely

have been reckoned; in the Great Chagos Bank there is not one. On the other hand, in the lagoons of some of

the great southern Maldiva atolls, although thickly studded with reefs, every one without exception rises to

the surface; and on an average there are less than two submerged reefs in each atoll; in the northern atolls,

however, the submerged lagoonreefs are not quite so rare. The submerged reefs in the Chagos atolls

generally have from one to seven fathoms water on them, but some have from seven to ten. Most of them are

small with very steep sides (Some of these statements were not communicated to me verbally by Captain

Moresby, but are taken from the MS. account before alluded to, of the Chagos Group.); at Peros Banhos they

rise from a depth of about thirty fathoms, and some of them in the Great Chagos Bank from above forty

fathoms; they are covered, Captain Moresby informs me, with living and healthy coral, two and three feet

high, consisting of several species. Why then have not these lagoonreefs reached the surface, like the

innumerable ones in the atolls above named? If we attempt to assign any difference in their external

conditions, as the cause of this diversity, we are at once baffled. The lagoon of Diego Garcia is not deep, and

is almost wholly surrounded by its reef; Peros Banhos is very deep, much larger, with many wide passages

communicating with the open sea. On the other hand, of those atolls, in which all or nearly all the

lagoonreefs have reached the surface, some are small, others large, some shallow, others deep, some

Captain Moresby informs me that he has seen a French chart of Diego Garcia made eighty years before his

survey, and apparently very accurate; and from it he infers, that during this interval there has not been the

smallest change in the depth on any of the knolls within the lagoon. It is also known that during the last

fiftyone years, the eastern channel into the lagoon has neither become narrower, nor decreased in depth; and

as there are numerous small knolls of living coral within it, some change might have been anticipated.

Moreover, as the whole reef round the lagoon of this atoll has been converted into landan unparalleled

case, I believe, in an atoll of such large size,and as the strip of land is for considerable spaces more than

half a mile widealso a very unusual circumstance,we have the best possible evidence, that Diego Garcia

has remained at its present level for a very long period. With this fact, and with the knowledge that no

sensible change has taken place during eighty years in the coralknolls, and considering that every single reef

has reached the surface in other atolls, which do not present the smallest appearance of being older than

Diego Garcia and Peros Banhos, and which are placed under the same external conditions with them, one is

led to conclude that these submerged reefs, although covered with luxuriant coral, have no tendency to grow

upwards, and that they would remain at their present levels for an almost indefinite period.

From the number of these knolls, from their position, size, and form, many of them being only one or two

hundred yards across, with a rounded outline, and precipitous sides,it is indisputable that they have been

formed by the growth of coral; and this makes the case much more remarkable. In Peros Banhos and in the

Great Chagos Bank, some of these almost columnar masses are 200 feet high, and their summits lie only from

two to eight fathoms beneath the surface; therefore, a small proportional amount more of growth would cause

them to attain the surface, like those numerous knolls, which rise from an equally great depth within the

Maldiva atolls. We can hardly suppose that time has been wanting for the upward growth of the coral, whilst

in Diego Garcia, the broad annular strip of land, formed by the continued accumulation of detritus, shows

how long this atoll has remained at its present level. We must look to some other cause than the rate of

growth; and I suspect it will be found in the reefs being formed of different species of corals, adapted to live

The Great Chagos Bank is situated in the centre of the Chagos Group, and the Pitt and Speaker Banks at its

two extreme points. These banks resemble atolls, except in their external rim being about eight fathoms

submerged, and in being formed of dead rock, with very little living coral on it: a portion nine miles long of

the annular reef of Peros Banhos atoll is in the same condition. These facts, as will hereafter be shown, render

it very probable that the whole group at some former period subsided seven or eight fathoms; and that the

coral perished on the outer margin of those atolls which are now submerged, but that it continued alive, and

grew up to the surface on those which are now perfect. If these atolls did subside, and if from the suddenness

of the movement or from any other cause, those corals which are better adapted to live at a certain depth than

at the surface, once got possession of the knolls, supplanting the former occupants, they would exert little or

no tendency to grow upwards. To illustrate this, I may observe, that if the corals of the upper zone on the

outer edge of Keeling atoll were to perish, it is improbable that those of the lower zone would grow to the

surface, and thus become exposed to conditions for which they do not appear to be adapted. The conjecture,

that the corals on the submerged knolls within the Chagos atolls have analogous habits with those of the

lower zone outside Keeling atoll, receives some support from a remark by Captain Moresby, namely, that

they have a different appearance from those on the reefs in the Maldiva atolls, which, as we have seen, all rise

to the surface: he compares the kind of difference to that of the vegetation under different climates. I have

entered at considerable length into this case, although unable to throw much light on it, in order to show that

an equal tendency to upward growth ought not to be attributed to all coralreefs,to those situated at

different depths,to those forming the ring of an atoll or those on the knolls within a lagoon,to those in

one area and those in another. The inference, therefore, that one reef could not grow up to the surface within a

given time, because another, not known to be covered with the same species of corals, and not known to be

placed under conditions exactly the same, has not within the same time reached the surface, is unsound.

The remark made at the close of the last section, naturally leads to this division of our subject, which has not,

I think, hitherto been considered under a right point of view. Ehrenberg (Ehrenberg, as before cited, pages 39,

46, and 50.) has stated, that in the Red Sea, the corals only coat other rocks in a layer from one to two feet in

thickness, or at most to a fathom and a half; and he disbelieves that, in any case, they form, by their own

proper growth, great masses, stratum over stratum. A nearly similar observation has been made by MM.

Quoy and Gaimard ("Annales des Sciences Nat." tom. vi., page 28.), with respect to the thickness of some

upraised beds of coral, which they examined at Timor and some other places. Ehrenberg (Ehrenberg, ut sup.,

page 42.) saw certain large massive corals in the Red Sea, which he imagines to be of such vast antiquity, that

they might have been beheld by Pharaoh; and according to Mr. Lyell (Lyell's "Principles of Geology," book

iii., chapter xviii.) there are certain corals at Bermuda, which are known by tradition, to have been living for

centuries. To show how slowly coralreefs grow upwards, Captain Beechey (Beechey's "Voyage to the

Pacific," chapter viii.) has adduced the case of the Dolphin Reef off Tahiti, which has remained at the same

depth beneath the surface, namely about two fathoms and a half, for a period of sixtyseven years. There are

reefs in the Red Sea, which certainly do not appear (Ehrenberg, ut sup., page 43.) to have increased in

dimensions during the last halfcentury, and from the comparison of old charts with recent surveys, probably

not during the last two hundred years. These, and other similar facts, have so strongly impressed many with

the belief of the extreme slowness of the growth of corals, that they have even doubted the possibility of

islands in the great oceans having been formed by their agency. Others, again, who have not been

overwhelmed by this difficulty, have admitted that it would require thousands, and tens of thousands of years,

to form a mass, even of inconsiderable thickness; but the subject has not, I believe, been viewed in the proper

That masses of considerable thickness have been formed by the growth of coral, may be inferred with

certainty from the following facts. In the deep lagoons of Peros Banhos and of the Great Chagos Bank, there

are, as already described, small steepsided knolls covered with living coral. There are similar knolls in the

southern Maldiva atolls, some of which, as Captain Moresby assures me, are less than a hundred yards in

diameter, and rise to the surface from a depth of between two hundred and fifty and three hundred feet.

Considering their number, form, and position, it would be preposterous to suppose that they are based on

pinnacles of any rock, not of coral formation; or that sediment could have been heaped up into such small and

steep isolated cones. As no kind of living coral grows above the height of a few feet, we are compelled to

suppose that these knolls have been formed by the successive growth and death of many individuals,first

one being broken off or killed by some accident, and then another, and one set of species being replaced by

another set with different habits, as the reef rose nearer the surface, or as other changes supervened. The

spaces between the corals would become filled up with fragments and sand, and such matter would probably

soon be consolidated, for we learn from Lieutenant Nelson ("Geological Transactions," volume v., page

113.), that at Bermuda a process of this kind takes place beneath water, without the aid of evaporation. In

reefs, also, of the barrier class, we may feel sure, as I have shown, that masses of great thickness have been

formed by the growth of the coral; in the case of Vanikoro, judging only from the depth of the moat between

the land and the reef, the wall of coralrock must be at least three hundred feet in vertical thickness.

It is unfortunate that the upraised coralislands in the Pacific have not been examined by a geologist. The

cliffs of Elizabeth Island, in the Low Archipelago, are eighty feet high, and appear, from Captain Beechey's

description, to consist of a homogeneous coralrock. From the isolated position of this island, we may safely

infer that it is an upraised atoll, and therefore that it has been formed by masses of coral, grown together.

Savage Island seems, from the description of the younger Forster (Forster's "Voyage round the World with

Cook," volume ii., pages 163, 167.), to have a similar structure, and its shores are about forty feet high: some

of the Cook Islands also appear (Williams's "Narrative of Missionary Enterprise," page 30.) to be similarly

composed. Captain Belcher, R.N., in a letter which Captain Beaufort showed me at the admiralty, speaking of

Bow atoll, says, "I have succeeded in boring fortyfive feet through coralsand, when the auger became

jammed by the falling in of the surrounding CREAMY matter." On one of the Maldiva atolls, Captain

Moresby bored to a depth of twentysix feet, when his auger also broke: he has had the kindness to give me

the matter brought up; it is perfectly white, and like finely triturated coralrock.

In my description of Keeling atoll, I have given some facts, which show that the reef probably has grown

outwards; and I have found, just within the outer margin, the great mounds of Porites and of Millepora, with

their summits lately killed, and their sides subsequently thickened by the growth of the coral: a layer, also, of

Nullipora had already coated the dead surface. As the external slope of the reef is the same round the whole

of this atoll, and round many other atolls, the angle of inclination must result from an adaption between the

growing powers of the coral, and the force of the breakers, and their action on the loose sediment. The reef,

therefore, could not increase outwards, without a nearly equal addition to every part of the slope, so that the

original inclination might be preserved, and this would require a large amount of sediment, all derived from

the wear of corals and shells, to be added to the lower part. Moreover, at Keeling atoll, and probably in many

other cases, the different kinds of corals would have to encroach on each other; thus the Nulliporae cannot

increase outwards without encroaching on the Porites and Millepora complanata, as is now taking place; nor

these latter without encroaching on the strongly branched Madreporet, the Millepora alcicornis, and some

Astraeas; nor these again without a foundation being formed for them within the requisite depth, by the

accumulation of sediment. How slow, then, must be the ordinary lateral or outward growth of such reefs. But

off Christmas atoll, where the sea is much more shallow than is usual, we have good reason to believe that,

within a period not very remote, the reef has increased considerably in width. The land has the extraordinary

breadth of three miles; it consists of parallel ridges of shells and broken corals, which furnish "an

incontestable proof," as observed by Cook (Cook's "Third Voyage," book III., chapter x.), "that the island has

been produced by accessions from the sea, and is in a state of increase." The land is fronted by a coralreef,

and from the manner in which islets are known to be formed, we may feel confident that the reef was not

three miles wide, when the first, or most backward ridge, was thrown up; and, therefore, we must conclude

that the reef has grown outwards during the accumulation of the successive ridges. Here then, a wall of

coralrock of very considerable breadth has been formed by the outward growth of the living margin, within

a period during which ridges of shells and corals, lying on the bare surface, have not decayed. There can be

little doubt, from the account given by Captain Beechey, that Matilda atoll, in the Low Archipelago, has been

converted in the space of thirtyfour years, from being, as described by the crew of a wrecked whaling

vessel, a "reef of rocks" into a lagoonisland, fourteen miles in length, with "one of its sides covered nearly

the whole way with high trees." (Beechey's "Voyage to the Pacific," chapter vii. and viii.) The islets, also, on

Keeling atoll, it has been shown, have increased in length, and since the construction of an old chart, several

of them have become united into one long islet; but in this case, and in that of Matilda atoll, we have no

proof, and can only infer as probable, that the reef, that is the foundation of the islets, has increased as well as

After these considerations, I attach little importance, as indicating the ordinary and still less the possible rate

of OUTWARD growth of coralreefs, to the fact that certain reefs in the Red Sea have not increased during a

long interval of time; or to other such cases, as that of Ouluthy atoll in the Caroline group, where every islet,

described a thousand years before by Cantova was found in the same state by Lutke (F. Lutke's "Voyage

autour du Monde." In the group Elato, however, it appears that what is now the islet Falipi, is called in

Cantova's Chart, the Banc de Falipi. It is not stated whether this has been caused by the growth of coral, or by

the accumulation of sand.),without it could be shown that, in these cases, the conditions were favourable to

the vigorous and unopposed growth of the corals living in the different zones of depth, and that a proper basis

for the extent of the reef was present. The former conditions must depend on many contingencies, and in the

deep oceans where coral formations most abound, a basis within the requisite depth can rarely be present.

Nor do I attach any importance to the fact of certain submerged reefs, as those off Tahiti, or those within

Diego Garcia not now being nearer the surface than they were many years ago, as an indication of the rate

under favourable circumstances of the UPWARD growth of reefs; after it has been shown, that all the reefs

have grown to the surface in some of the Chagos atolls, but that in neighbouring atolls which appear to be of

equal antiquity and to be exposed to the same external conditions, every reef remains submerged; for we are

almost driven to attribute this to a difference, not in the rate of growth, but in the habits of the corals in the

In an oldstanding reef, the corals, which are so different in kind on different parts of it, are probably all

adapted to the stations they occupy, and hold their places, like other organic beings, by a struggle one with

another, and with external nature; hence we may infer that their growth would generally be slow, except

under peculiarly favourable circumstances. Almost the only natural condition, allowing a quick upward

growth of the whole surface of a reef, would be a slow subsidence of the area in which it stood; if, for

instance, Keeling atoll were to subside two or three feet, can we doubt that the projecting margin of live

coral, about half an inch in thickness, which surrounds the dead upper surfaces of the mounds of Porites,

would in this case form a concentric layer over them, and the reef thus increase upwards, instead of, as at

present, outwards? The Nulliporae are now encroaching on the Porites and Millepora, but in this case might

we not confidently expect that the latter would, in their turn, encroach on the Nulliporae? After a subsidence

of this kind, the sea would gain on the islets, and the great fields of dead but upright corals in the lagoon,

would be covered by a sheet of clear water; and might we not then expect that these reefs would rise to the

surface, as they anciently did when the lagoon was less confined by islets, and as they did within a period of

ten years in the schoonerchannel, cut by the inhabitants? In one of the Maldiva atolls, a reef, which within a

very few years existed as an islet bearing cocoanut trees, was found by Lieutenant Prentice "ENTIRELY

COVERED WITH LIVE CORAL AND MADREPORE." The natives believe that the islet was washed away

by a change in the currents, but if, instead of this, it had quietly subsided, surely every part of the island

which offered a solid foundation, would in a like manner have become coated with living coral.

Through steps such as these, any thickness of rock, composed of a singular intermixture of various kinds of

corals, shells, and calcareous sediment, might be formed; but without subsidence, the thickness would

necessarily be determined by the depth at which the reefbuilding polypifers can exist. If it be asked, at what

rate in years I suppose a reef of coral favourably circumstanced could grow up from a given depth; I should

answer, that we have no precise evidence on this point, and comparatively little concern with it. We see, in

innumerable points over wide areas, that the rate has been sufficient, either to bring up the reefs from various

depths to the surface, or, as is more probable, to keep them at the surface, during progressive subsidences;

and this is a much more important standard of comparison than any cycle of years.

It may, however, be inferred from the following facts, that the rate in years under favourable circumstances

would be very far from slow. Dr. Allan, of Forres, has, in his MS. Thesis deposited in the library of the

Edinburgh University (extracts from which I owe to the kindness of Dr. Malcolmson), the following account

of some experiments, which he tried during his travels in the years 1830 to 1832 on the east coast of

Madagascar. "To ascertain the rise and progress of the coralfamily, and fix the number of species met with

at Foul Point (latitude 17 deg 40') twenty species of coral were taken off the reef and planted apart on a

sandbank THREE FEET DEEP AT LOW WATER. Each portion weighed ten pounds, and was kept in its

place by stakes. Similar quantities were placed in a clump and secured as the rest. This was done in

December 1830. In July following, each detached mass was nearly level with the sea at low water, quite

immovable, and several feet long, stretching as the parent reef, with the coast current from north to south.

The masses accumulated in a clump were found equally increased, but some of the species in such unequal

ratios, as to be growing over each other." The loss of Dr. Allan's magnificent collection by shipwreck,

unfortunately prevents its being known to what genera these corals belonged; but from the numbers

experimented on, it is certain that all the more conspicuous kinds must have been included. Dr. Allan informs

me, in a letter, that he believes it was a Madrepora, which grew most vigorously. One may be permitted to

suspect that the level of the sea might possibly have been somewhat different at the two stated periods;

nevertheless, it is quite evident that the growth of the tenpound masses, during the six or seven months, at

the end of which they were found immovably fixed (It is stated by De la Beche ("Geological Manual," page

143), on the authority of Mr. Lloyd, who surveyed the Isthmus of Panama, that some specimens of

Polypifers, placed by him in a sheltered pool of water, were found in the course of a few days firmly fixed by

the secretion of a stony matter, to the bottom) and several feet in length, must have been very great. The fact

of the different kinds of coral, when placed in one clump, having increased in extremely unequal ratios, is

very interesting, as it shows the manner in which a reef, supporting many species of coral, would probably be

affected by a change in the external conditions favouring one kind more than another. The growth of the

masses of coral in N. and S. lines parallel to the prevailing currents, whether due to the drifting of sediment or

A fact, communicated to me by Lieutenant Wellstead, I.N., in some degree corroborates the result of Dr.

Allan's experiments: it is, that in the Persian Gulf a ship had her copper bottom encrusted in the course of

twenty months with a layer of coral, TWO FEET in thickness, which it required great force to remove, when

the vessel was docked: it was not ascertained to what order this coral belonged. The case of the

schoonerchannel choked up with coral in an interval of less than ten years, in the lagoon of Keeling atoll,

should be here borne in mind. We may also infer, from the trouble which the inhabitants of the Maldiva atolls

take to root out, as they express it, the coralknolls from their harbours, that their growth can hardly be very

slow. (Mr. Stutchbury ("West of England Journal", No. I., page 50.) has described a specimen of Agaricia,

"weighing 2 lbs. 9 oz., which surrounds a species of oyster, whose age could not be more than two years, and

yet is completely enveloped by this dense coral." I presume that the oyster was living when the specimen was

procured; otherwise the fact tells nothing. Mr. Stutchbury also mentions an anchor, which had become

entirely encrusted with coral in fifty years; other cases, however, are recorded of anchors which have long

remained amidst coralreefs without having become coated. The anchor of the "Beagle", in 1832, after

having been down exactly one month at Rio de Janeiro, was so thickly coated by two species of Tubularia,

that large spaces of the iron were entirely concealed; the tufts of this horny zoophyte were between two and

three inches in length. It has been attempted to compute, but I believe erroneously, the rate of growth of a

reef, from the fact mentioned by Captain Beechey, of the Chama gigas being embedded in coralrock. But it

should be remembered, that some species of this genus invariably live, both whilst young and old, in cavities,

which the animal has the power of enlarging with its growth. I saw many of these shells thus embedded in the

outer "flat" of Keeling atoll, which is composed of dead rock; and therefore the cavities in this case had no

relation whatever with the growth of coral. M. Lesson, also, speaking of this shell (Partie Zoolog. "Voyage de

la 'Coquille'"), has remarked, "que constamment ses valves etaient engages completement dans la masse des

From the facts given in this section, it may be concluded, first, that considerable thicknesses of rock have

certainly been formed within the present geological area by the growth of coral and the accumulation of its

detritus; and, secondly, that the increase of individual corals and of reefs, both outwards or horizontally and

upwards or vertically, under the peculiar conditions favourable to such increase, is not slow, when referred

either to the standard of the average oscillations of level in the earth's crust, or to the more precise but less

I have already described in detail, which might have appeared trivial, the nature of the bottom of the sea

immediately surrounding Keeling atoll; and I will now describe with almost equal care the soundings off the

fringingreefs of Mauritius. I have preferred this arrangement, for the sake of grouping together facts of a

similar nature. I sounded with the wide bellshaped lead which Captain Fitzroy used at Keeling Island, but

my examination of the bottom was confined to a few miles of coast (between Port Louis and Tomb Bay) on

the leeward side of the island. The edge of the reef is formed of great shapeless masses of branching

Madrepores, which chiefly consist of two species,apparently M. corymbosa and pocillifera, mingled

with a few other kinds of coral. These masses are separated from each other by the most irregular gullies and

cavities, into which the lead sinks many feet. Outside this irregular border of Madrepores, the water deepens

gradually to twenty fathoms, which depth generally is found at the distance of from half to threequarters of

a mile from the reef. A little further out the depth is thirty fathoms, and thence the bank slopes rapidly into

the depths of the ocean. This inclination is very gentle compared with that outside Keeling and other atolls,

but compared with most coasts it is steep. The water was so clear outside the reef, that I could distinguish

every object forming the rugged bottom. In this part, and to a depth of eight fathoms, I sounded repeatedly,

and at each cast pounded the bottom with the broad lead, nevertheless the arming invariably came up

perfectly clean, but deeply indented. From eight to fifteen fathoms a little calcareous sand was occasionally

brought up, but more frequently the arming was simply indented. In all this space the two Madrepores above

mentioned, and two species of Astraea, with rather large stars, seemed the commonest kinds (Since the

preceding pages were printed off, I have received from Mr. Lyell a very interesting pamphlet, entitled

"Remarks upon Coral Formations," etc., by J. Couthouy, Boston, United States, 1842. There is a statement

(page 6), on the authority of the Rev. J. Williams, corroborating the remarks made by Ehrenberg and Lyell

(page 71 of this volume), on the antiquity of certain individual corals in the Red Sea and at Bermuda; namely,

that at Upolu, one of the Navigator Islands, "particular clumps of coral are known to the fishermen by name,

derived from either some particular configuration or tradition attached to them, and handed down from time

immemorial." With respect to the thickness of masses of coralrock, it clearly appears, from the descriptions

given by Mr. Couthouy (pages 34, 58) that Mangaia and Aurora Islands are upraised atolls, composed of

coral rock: the level summit of the former is about three hundred feet, and that of Aurora Island is two

hundred feet above the sealevel.); and it must be noticed that twice at the depth of fifteen fathoms, the

arming was marked with a clean impression of an Astraea. Besides these lithophytes, some fragments of the

Millepora alcicornis, which occurs in the same relative position at Keeling Island, were brought up; and in the

deeper parts there were large beds of a Seriatopora, different from S. subulata, but closely allied to it. On the

beach within the reef, the rolled fragments consisted chiefly of the corals just mentioned, and of a massive

Porites, like that at Keeling atoll, of a Meandrina, Pocillopora verrucosa, and of numerous fragments of

Nullipora. From fifteen to twenty fathoms the bottom was, with few exceptions, either formed of sand, or

thickly covered with Seriatopora: this delicate coral seems to form at these depths extensive beds unmingled

with any other kind. At twenty fathoms, one sounding brought up a fragment of Madrepora apparently M.

pocillifera, and I believe it is the same species (for I neglected to bring specimens from both stations) which

mainly forms the upper margin of the reef; if so, it grows in depths varying from 0 to 20 fathoms. Between 20

and 23 fathoms I obtained several soundings, and they all showed a sandy bottom, with one exception at 30

fathoms, when the arming came up scooped out, as if by the margin of a large Caryophyllia. Beyond 33

fathoms I sounded only once; and from 86 fathoms, at the distance of one mile and a third from the edge of

the reef, the arming brought up calcareous sand with a pebble of volcanic rock. The circumstance of the

arming having invariably come up quite clean, when sounding within a certain number of fathoms off the

reefs of Mauritius and Keeling atoll (eight fathoms in the former case, and twelve in the latter) and of its

having always come up (with one exception) smoothed and covered with sand, when the depth exceeded

twenty fathoms, probably indicates a criterion, by which the limits of the vigorous growth of coral might in

all cases be readily ascertained. I do not, however, suppose that if a vast number of soundings were obtained

round these islands, the limit above assigned would be found never to vary, but I conceive the facts are

sufficient to show, that the exceptions would be few. The circumstance of a GRADUAL change, in the two

cases, from a field of clean coral to a smooth sandy bottom, is far more important in indicating the depth at

which the larger kinds of coral flourish than almost any number of separate observations on the depth, at

which certain species have been dredged up. For we can understand the gradation, only as a prolonged

struggle against unfavourable conditions. If a person were to find the soil clothed with turf on the banks of a

stream of water, but on going to some distance on one side of it, he observed the blades of grass growing

thinner and thinner, with intervening patches of sand, until he entered a desert of sand, he would safely

conclude, especially if changes of the same kind were noticed in other places, that the presence of the water

was absolutely necessary to the formation of a thick bed of turf: so may we conclude, with the same feeling

of certainty, that thick beds of coral are formed only at small depths beneath the surface of the sea.

I have endeavoured to collect every fact, which might either invalidate or corroborate this conclusion.

Captain Moresby, whose opportunities for observation during his survey of the Maldiva and Chagos

Archipelagoes have been unrivalled, informs me, that the upper part or zone of the steepsided reefs, on the

inner and outer coasts of the atolls in both groups, invariably consists of coral, and the lower parts of sand. At

seven or eight fathoms depth, the bottom is formed, as could be seen through the clear water, of great living

masses of coral, which at about ten fathoms generally stand some way apart from each other, with patches of

white sand between them, and at a little greater depth these patches become united into a smooth steep slope,

without any coral. Captain Moresby, also, informs me in support of his statement, that he found only decayed

coral on the Padua Bank (northern part of the Laccadive group) which has an average depth between

twentyfive and thirtyfive fathoms, but that on some other banks in the same group with only ten or twelve

fathoms water on them (for instance, the Tillacapeni bank), the coral was living.

With regard to the coralreefs in the Red Sea, Ehrenberg has the following passage:"The living corals do

not descend there into great depths. On the edges of islets and near reefs, where the depth was small, very

many lived; but we found no more even at six fathoms. The pearlfishers at Yemen and Massaua asserted

that there was no coral near the pearlbanks at nine fathoms depth, but only sand. We were not able to

institute any more special researches." (Ehrenberg, "Uber die Natur," etc., page 50.) I am, however, assured

both by Captain Moresby and Lieutenant Wellstead, that in the more northern parts of the Red Sea, there are

extensive beds of living coral at a depth of twentyfive fathoms, in which the anchors of their vessels were

frequently entangled. Captain Moresby attributes the less depth, at which the corals are able to live in the

places mentioned by Ehrenberg, to the greater quantity of sediment there; and the situations, where they were

flourishing at the depth of twentyfive fathoms, were protected, and the water was extraordinarily limpid. On

the leeward side of Mauritius where I found the coral growing at a somewhat greater depth than at Keeling

atoll, the sea, owing apparently to its tranquil state, was likewise very clear. Within the lagoons of some of

the Marshall atolls, where the water can be but little agitated, there are, according to Kotzebue, living beds of

coral in twentyfive fathoms. From these facts, and considering the manner in which the beds of clean coral

off Mauritius, Keeling Island, the Maldiva and Chagos atolls, graduated into a sandy slope, it appears very

probable that the depth, at which reefbuilding polypifers can exist, is partly determined by the extent of

inclined surface, which the currents of the sea and the recoiling waves have the power to keep free from

MM. Quoy and Gaimard ("Annales des Sci. Nat." tom. vi.) believe that the growth of coral is confined within

very limited depths; and they state that they never found any fragment of an Astraea (the genus they consider

most efficient in forming reefs) at a depth above twentyfive or thirty feet. But we have seen that in several

places the bottom of the sea is paved with massive corals at more than twice this depth; and at fifteen fathoms

(or twice this depth) off the reefs of Mauritius, the arming was marked with the distinct impression of a living

Astraea. Millepora alcicornis lives in from 0 to 12 fathoms, and the genera Madrepora and Seriatopora from 0

to 20 fathoms. Captain Moresby has given me a specimen of Sideropora scabra (Porites of Lamarck) brought

up alive from 17 fathoms. Mr. Couthouy ("Remarks on Coral Formations," page 12.) states that he has

dredged up on the Bahama banks considerable masses of Meandrina from 16 fathoms, and he has seen this

coral growing in 20 fathoms. A Caryophyllia, half an inch in diameter, was dredged up alive from 80 fathoms

off Juan Fernandez (latitude 33 deg S.) by Captain P.P. King (I am indebted to Mr. Stokes for having kindly

communicated this fact to me, together with much other valuable information.): this is the most remarkable

fact with which I am acquainted, showing the depth at which a genus of corals often found on reefs, can exist.

We ought, however, to feel less surprise at this fact, as Caryophyllia alone of the lamelliform genera, ranges

far beyond the tropics; it is found in Zetland (Fleming's "British Animals," genus Caryophyllia.) in Latitude

60 deg N. in deep water, and I procured a small species from Tierra del Fuego in Latitude 53 deg S. Captain

Beechey informs me, that branches of pink and yellow coral were frequently brought up from between twenty

and twentyfive fathoms off the Low atolls; and Lieutenant Stokes, writing to me from the N.W. coast of

Australia, says that a strongly branched coral was procured there from thirty fathoms; unfortunately it is not

(I will record in the form of a note all the facts that I have been able to collect on the depths, both within and

without the tropics, at which those corals and corallines can live, which there is no reason to suppose ever

(In the following list the name of the Zoophyte is followed by the depth in fathoms, the country and degrees

S. latitude, and the authority. Where no authority is given, the observation is Darwin's own.)

CELLARIA, A minute scarlet encrusting species, found living, 190, Keeling Atoll, 12.

CELLEPORA, several species, and allied subgeneric forms, 40 and 57, Chonos Archipelago 45.

RETEPORA, 100, Cape of Good Hope 34, Quoy and Gaimard, "Ann. Scien. Nat." tome vi., page 284.

MILLEPORA, a strong coral with cylindrical branches, of a pink colour, about two inches high, resembling

in the form of its orifices M. aspera of Lamarck, 94 and 30, E. Chiloe 43, Tierra del Fuego 53.

CORALIUM, 120, Barbary 33 N., Peyssonel in paper read to Royal Society May 1752.

GORGONIA (or an allied form), 160, Abrolhos on the coast of Brazil 18, Captain Beechey informed me of

Ellis ("Nat. Hist. of Coralline," page 96) states that Ombellularia was procured in latitude 79 deg N.

STICKING to a LINE from the depth of 236 fathoms; hence this coral either must have been floating loose,

or was entangled in stray line at the bottom. Off Keeling atoll a compound Ascidia (Sigillina) was brought up

from 39 fathoms, and a piece of sponge, apparently living, from 70, and a fragment of Nullipora also

apparently living from 92 fathoms. At a greater depth than 90 fathoms off this coral island, the bottom was

thickly strewed with joints of Halimeda and small fragments of other Nulliporae, but all dead. Captain B.

Allen, R.N., informs me that in the survey of the West Indies it was noticed that between the depth of 10 and

200 fathoms, the sounding lead very generally came up coated with the dead joints of a Halimeda, of which

he showed me specimens. Off Pernambuco, in Brazil, in about twelve fathoms, the bottom was covered with

fragments dead and alive of a dull red Nullipora, and I infer from Roussin's chart, that a bottom of this kind

extends over a wide area. On the beach, within the coralreefs of Mauritius, vast quantities of fragments of

Nulliporae were piled up. From these facts it appears, that these simply organized bodies are amongst the

Although the limit of depth, at which each particular kind of coral ceases to exist, is far from being accurately

known; yet when we bear in mind the manner in which the clumps of coral gradually became infrequent at

about the same depth, and wholly disappeared at a greater depth than twenty fathoms, on the slope round

Keeling atoll, on the leeward side of the Mauritius, and at rather less depth, both without and within the atolls

of the Maldiva and Chagos Archipelagoes; and when we know that the reefs round these islands do not differ

from other coral formations in their form and structure, we may, I think, conclude that in ordinary cases,

reefbuilding polypifers do not flourish at greater depths than between twenty and thirty fathoms.

It has been argued ("Journal of the Royal Geographical Society," 1831, page 218.) that reefs may possibly

rise from very great depths through the means of small corals, first making a platform for the growth of the

stronger kinds. This, however, is an arbitrary supposition: it is not always remembered, that in such cases

there is an antagonist power in action, namely, the decay of organic bodies, when not protected by a covering

of sediment, or by their own rapid growth. We have, moreover, no right to calculate on unlimited time for the

accumulation of small organic bodies into great masses. Every fact in geology proclaims that neither the land,

nor the bed of the sea retain for indefinite periods the same level. As well might it be imagined that the

British Seas would in time become choked up with beds of oysters, or that the numerous small corallines off

the inhospitable shores of Tierra del Fuego would in time form a solid and extensive coralreef.

The atolls of the larger archipelagoes are not formed on submerged craters, or on banks of

sediment.Immense areas interspersed with atolls.Their subsidence.The effects of storms and

earthquakes on atolls.Recent changes in their state.The origin of barrierreefs and of atolls.Their

relative forms.The stepformed ledges and walls round the shores of some lagoons.The ringformed

reefs of the Maldiva atolls.The submerged condition of parts or of the whole of some annular reefs.The

disseverment of large atolls.The union of atolls by linear reefs.The Great Chagos Bank.Objections

from the area and amount of subsidence required by the theory, considered.The probable composition of

The naturalists who have visited the Pacific, seem to have had their attention riveted by the lagoonislands,

or atolls,those singular rings of coralland which rise abruptly out of the unfathomable oceanand have

passed over, almost unnoticed, the scarcely less wonderful encircling barrierreefs. The theory most

generally received on the formation of atolls, is that they are based on submarine craters; but where can we

find a crater of the shape of Bow atoll, which is five times as long as it is broad (Plate I., Figure 4); or like

that of Menchikoff Island (Plate II., Figure 3.), with its three loops, together sixty miles in length; or like

Rimsky Korsacoff, narrow, crooked, and fiftyfour miles long; or like the northern Maldiva atolls, made up

of numerous ringformed reefs, placed on the margin of a disc,one of which discs is eightyeight miles in

length, and only from ten to twenty in breadth? It is, also, not a little improbable, that there should have

existed as many craters of immense size crowded together beneath the sea, as there are now in some parts

atolls. But this theory lies under a greater difficulty, as will be evident, when we consider on what

foundations the atolls of the larger archipelagoes rest: nevertheless, if the rim of a crater afforded a basis at

the proper depth, I am far from denying that a reef like a perfectly characterised atoll might not be formed;

some such, perhaps, now exist; but I cannot believe in the possibility of the greater number having thus

An earlier and better theory was proposed by Chamisso (Kotzebue's "First Voyage," volume iii., page 331.);

he supposes that as the more massive kinds of corals prefer the surf, the outer portions, in a reef rising from a

submarine basis, would first reach the surface and consequently form a ring. But on this view it must be

assumed, that in every case the basis consists of a flat bank; for if it were conically formed, like a

mountainous mass, we can see no reason why the coral should spring up from the flanks, instead of from the

central and highest parts: considering the number of the atolls in the Pacific and Indian Oceans, this

assumption is very improbable. As the lagoons of atolls are sometimes even more than forty fathoms deep, it

must, also, be assumed on this view, that at a depth at which the waves do not break, the coral grows more

vigorously on the edges of a bank than on its central part; and this is an assumption without any evidence in

support of it. I remarked, in the third chapter, that a reef, growing on a detached bank, would tend to assume

an atolllike structure; if, therefore, corals were to grow up from a bank, with a level surface some fathoms

submerged, having steep sides and being situated in a deep sea, a reef not to be distinguished from an atoll,

might be formed: I believe some such exist in the West Indies. But a difficulty of the same kind with that

affecting the crater theory, runners, as we shall presently see, this view inapplicable to the greater number of

No theory worthy of notice has been advanced to account for those barrierreefs, which encircle islands of

moderate dimensions. The great reef which fronts the coast of Australia has been supposed, but without any

special facts, to rest on the edge of a submarine precipice, extending parallel to the shore. The origin of the

third class or of fringingreefs presents, I believe, scarcely any difficulty, and is simply consequent on the

polypifers not growing up from great depths, and their not flourishing close to gently shelving beaches where

What cause, then, has given to atolls and barrierreefs their characteristic forms? Let us see whether an

important deduction will not follow from the consideration of these two circumstances, first, the

reefbuilding corals flourishing only at limited depths; and secondly, the vastness of the areas interspersed

with coralreefs and coralislets, none of which rise to a greater height above the level of the sea, than that

attained by matter thrown up by the waves and winds. I do not make this latter statement vaguely; I have

carefully sought for descriptions of every island in the intertropical seas; and my task has been in some

degree abridged by a map of the Pacific, corrected in 1834 by MM. D'Urville and Lottin, in which the low

islands are distinguished from the high ones (even from those much less than a hundred feet in height) by

being written without a capital letter; I have detected a few errors in this map, respecting the height of some

of the islands, which will be noticed in the Appendix, where I treat of coral formations in geographical order.

To the Appendix, also, I must refer for a more particular account of the data on which the statements on the

next page are grounded. I have ascertained, and chiefly from the writings of Cook, Kotzebue, Bellinghausen,

Duperrey, Beechey, and Lutke, regarding the Pacific; and from Moresby (See also Captain Owen's and

Lieutenant Wood's papers in the "Geographical Journal", on the Maldiva and Laccadive Archipelagoes.

These officers particularly refer to the lowness of the islets; but I chiefly ground my assertion respecting these

two groups, and the Chagos group, from information communicated to me by Captain Moresby.) with respect

to the Indian Ocean, that in the following cases the term "low island" strictly means land of the height

commonly attained by matter thrown up by the winds and the waves of an open sea. If we draw a line (the

plan I have always adopted) joining the external atolls of that part of the Low Archipelago in which the

islands are numerous, the figure will be a pointed ellipse (reaching from Hood to Lazaref Island), of which

the longer axis is 840 geographical miles, and the shorter 420 miles; in this space (I find from Mr. Couthouy's

pamphlet (page 58) that Aurora Island is about two hundred feet in height; it consists of coralrock, and

seems to have been formed by the elevation of an atoll. It lies northeast of Tahiti, close without the line

bounding the space coloured dark blue in the map appended to this volume. Honden Island, which is situated

in the extreme northwest part of the Low Archipelago, according to measurements made on board the

"Beagle", whilst sailing by, is 114 feet from the SUMMIT OF THE TREES to the water's edge. This island

appeared to resemble the other atolls of the group.) none of the innumerable islets united into great rings rise

above the stated level. The Gilbert group is very narrow, and 300 miles in length. In a prolonged line from

this group, at the distance of 240 miles, is the Marshall Archipelago, the figure of which is an irregular

square, one end being broader than the other; its length is 520 miles, with an average width of 240; these two

groups together are 1,040 miles in length, and all their islets are low. Between the southern end of the Gilbert

and the northern end of Low Archipelago, the ocean is thinly strewed with islands, all of which, as far as I

have been able to ascertain, are low; so that from nearly the southern end of the Low Archipelago, to the

northern end of the Marshall Archipelago, there is a narrow band of ocean, more than 4,000 miles in length,

containing a great number of islands, all of which are low. In the western part of the Caroline Archipelago,

there is a space of 480 miles in length, and about 100 broad, thinly interspersed with low islands. Lastly, in

the Indian Ocean, the archipelago of the Maldivas is 470 miles in length, and 60 in breadth; that of the

Laccadives is 150 by 100 miles; as there is a low island between these two groups, they may be considered as

one group of 1,000 miles in length. To this may be added the Chagos group of low islands, situated 280 miles

distant, in a line prolonged from the southern extremity of the Maldivas. This group, including the submerged

banks, is 170 miles in length and 80 in breadth. So striking is the uniformity in direction of these three

archipelagoes, all the islands of which are low, that Captain Moresby, in one of his papers, speaks of them as

parts of one great chain, nearly 1,500 miles long. I am, then, fully justified in repeating, that enormous

spaces, both in the Pacific and Indian Oceans, are interspersed with islands, of which not one rises above that

On what foundations, then, have these reefs and islets of coral been constructed? A foundation must

originally have been present beneath each atoll at that limited depth, which is indispensable for the first

growth of the reefbuilding polypifers. A conjecture will perhaps be hazarded, that the requisite bases might

have been afforded by the accumulation of great banks of sediment, which owing to the action of superficial

currents (aided possibly by the undulatory movement of the sea) did not quite reach the surface,as actually

appears to have been the case in some parts of the West Indian Sea. But in the form and disposition of the

groups of atolls, there is nothing to countenance this notion; and the assumption without any proof, that a

number of immense piles of sediment have been heaped on the floor of the great Pacific and Indian Oceans,

in their central parts far remote from land, and where the dark blue colour of the limpid water bespeaks its

The many widelyscattered atolls must, therefore, rest on rocky bases. But we cannot believe that the broad

summit of a mountain lies buried at the depth of a few fathoms beneath every atoll, and nevertheless

throughout the immense areas abovenamed, with not one point of rock projecting above the level of the sea;

for we may judge with some accuracy of mountains beneath the sea, by those on the land; and where can we

find a single chain several hundred miles in length and of considerable breadth, much less several such

chains, with their many broad summits attaining the same height, within from 120 to 180 feet? If the data be

thought insufficient, on which I have grounded my belief, respecting the depth at which the reefbuilding

polypifers can exist, and it be assumed that they can flourish at a depth of even one hundred fathoms, yet the

weight of the above argument is but little diminished, for it is almost equally improbable, that as many

submarine mountains, as there are low islands in the several great and widely separated areas above specified,

should all rise within six hundred feet of the surface of the sea and not one above it, as that they should be of

the same height within the smaller limit of one or two hundred feet. So highly improbable is this supposition,

that we are compelled to believe, that the bases of the many atolls did never at any one period all lie

submerged within the depth of a few fathoms beneath the surface, but that they were brought into the

requisite position or level, some at one period and some at another, through movements in the earth's crust.

But this could not have been effected by elevation, for the belief that points so numerous and so widely

separated were successively uplifted to a certain level, but that not one point was raised above that level, is

quite as improbable as the former supposition, and indeed differs little from it. It will probably occur to those

who have read Ehrenberg's account of the Reefs of the Red Sea, that many points in these great areas may

have been elevated, but that as soon as raised, the protuberant parts were cut off by the destroying action of

the waves: a moment's reflection, however, on the basinlike form of the atolls, will show that this is

impossible; for the upheaval and subsequent abrasion of an island would leave a flat disc, which might

become coated with coral, but not a deeply concave surface; moreover, we should expect to see, in some parts

at least, the rock of the foundation brought to the surface. If, then, the foundations of the many atolls were not

uplifted into the requisite position, they must of necessity have subsided into it; and this at once solves every

difficulty (The additional difficulty on the crater hypothesis before alluded to, will now be evident; for on this

view the volcanic action must be supposed to have formed within the areas specified a vast number of craters,

all rising within a few fathoms of the surface, and not one above it. The supposition that the craters were at

different times upraised above the surface, and were there abraded by the surf and subsequently coated by

corals, is subject to nearly the same objections with those given above in this paragraph; but I consider it

superfluous to detail all the arguments opposed to such a notion. Chamisso's theory, from assuming the

existence of so many banks, all lying at the proper depth beneath the water, is also vitally defective. The same

observation applies to an hypothesis of Lieutenant Nelson's ("Geolog. Trans." volume v., page 122), who

supposes that the ringformed structure is caused by a greater number of germs of corals becoming attached

to the declivity, than to the central plateau of a submarine bank: it likewise applies to the notion formerly

entertained (Forster's "Observ." page 151), that lagoonislands owe their peculiar form to the instinctive

tendencies of the polypifers. According to this latter view, the corals on the outer margin of the reef

instinctively expose themselves to the surf in order to afford protection to corals living in the lagoon, which

belong to other genera, and to other families!), for we may safely infer, from the facts given in the last

chapter, that during a gradual subsidence the corals would be favourably circumstanced for building up their

solid frame works and reaching the surface, as island after island slowly disappeared. Thus areas of immense

extent in the central and most profound parts of the great oceans, might become interspersed with

coralislets, none of which would rise to a greater height than that attained by detritus heaped up by the sea,

and nevertheless they might all have been formed by corals, which absolutely required for their growth a

It would be out of place here to do more than allude to the many facts, showing that the supposition of a

gradual subsidence over large areas is by no means improbable. We have the clearest proof that a movement

of this kind is possible, in the upright trees buried under the strata many thousand feet in thickness; we have

also every reason for believing that there are now large areas gradually sinking, in the same manner as others

are rising. And when we consider how many parts of the surface of the globe have been elevated within

recent geological periods, we must admit that there have been subsidences on a corresponding scale, for

otherwise the whole globe would have swollen. It is very remarkable that Mr. Lyell ("Principles of Geology,"

sixth edition, volume iii., page 386.), even in the first edition of his "Principles of Geology," inferred that the

amount of subsidence in the Pacific must have exceeded that of elevation, from the area of land being very

small relatively to the agents there tending to form it, namely, the growth of coral and volcanic action. But it

will be asked, are there any direct proofs of a subsiding movement in those areas, in which subsidence will

explain a phenomenon otherwise inexplicable? This, however, can hardly be expected, for it must ever be

most difficult, excepting in countries long civilised, to detect a movement, the tendency of which is to

conceal the part affected. In barbarous and semicivilised nations how long might not a slow movement,

even of elevation such as that now affecting Scandinavia, have escaped attention!

Mr. Williams (Williams's "Narrative of Missionary Enterprise," page 31.) insists strongly that the traditions

of the natives, which he has taken much pains in collecting, do not indicate the appearance of any new

islands: but on the theory of a gradual subsidence, all that would be apparent would be, the water sometimes

encroaching slowly on the land, and the land again recovering by the accumulation of detritus its former

extent, and perhaps sometimes the conversion of an atoll with coral islets on it, into a bare or into a sunken

annular reef. Such changes would naturally take place at the periods when the sea rose above its usual limits,

during a gale of more than ordinary strength; and the effects of the two causes would be hardly

distinguishable. In Kotzebue's "Voyage" there are accounts of islands, both in the Caroline and Marshall

Archipelagoes, which have been partly washed away during hurricanes; and Kadu, the native who was on

board one of the Russian vessels, said "he saw the sea at Radack rise to the feet of the cocoanut trees; but it

was conjured in time." (Kotzebue's "First Voyage," volume iii., page 168.) A storm lately entirely swept

away two of the Caroline islands, and converted them into shoals; it partly, also, destroyed two other islands.

(M. Desmoulins in "Comptes Rendus," 1840, page 837.) According to a tradition which was communicated

to Captain Fitzroy, it is believed in the Low Archipelago, that the arrival of the first ship caused a great

inundation, which destroyed many lives. Mr. Stutchbury relates, that in 1825, the western side of Chain Atoll,

in the same group, was completely devastated by a hurricane, and not less than 300 lives lost: "in this

instance it was evident, even to the natives, that the hurricane alone was not sufficient to account for the

violent agitation of the ocean." ("West of England Journal", No. I., page 35.) That considerable changes have

taken place recently in some of the atolls in the Low Archipelago, appears certain from the case already given

of Matilda Island: with respect to Whitsunday and Gloucester Islands in this same group, we must either

attribute great inaccuracy to their discoverer, the famous circumnavigator Wallis, or believe that they have

undergone a considerable change in the period of fiftynine years, between his voyage and that of Captain

Beechey's. Whitsunday Island is described by Wallis as "about four miles long, and three wide," now it is

only one mile and a half long. The appearance of Gloucester Island, in Captain Beechey's words (Beechey's

"Voyage to the Pacific," chapter vii., and Wallis's "Voyage in the 'Dolphin'," chapter iv.), has been accurately

described by its discoverer, but its present form and extent differ materially." Blenheim reef, in the Chagos

group, consists of a waterwashed annular reef, thirteen miles in circumference, surrounding a lagoon ten

fathoms deep: on its surface there were a few worn patches of conglomerate coralrock, of about the size of

hovels; and these Captain Moresby considered as being, without doubt, the last remnants of islets; so that

here an atoll has been converted into an atollformed reef. The inhabitants of the Maldiva Archipelago, as

long ago as 1605, declared, "that the high tides and violent currents were diminishing the number of the

islands" (See an extract from Pyrard's Voyage in Captain Owen's paper on the Maldiva Archipelago, in the

"Geographical Journal", volume ii., page 84.): and I have already shown, on the authority of Captain

Moresby, that the work of destruction is still in progress; but that on the other hand the first formation of

some islets is known to the present inhabitants. In such cases, it would be exceedingly difficult to detect a

Some of the archipelagoes of low coralislands are subject to earthquakes: Captain Moresby informs me that

they are frequent, though not very strong, in the Chagos group, which occupies a very central position in the

Indian Ocean, and is far from any land not of coral formation. One of the islands in this group was formerly

covered by a bed of mould, which, after an earthquake, disappeared, and was believed by the residents to

have been washed by the rain through the broken masses of underlying rock; the island was thus rendered

unproductive. Chamisso (See Chamisso, in Kotzebue's "First Voyage," volume iii., pages 182 and 136.)

states, that earthquakes are felt in the Marshall atolls, which are far from any high land, and likewise in the

islands of the Caroline Archipelago. On one of the latter, namely Oulleay atoll, Admiral Lutke, as he had the

kindness to inform me, observed several straight fissures about a foot in width, running for some hundred

yards obliquely across the whole width of the reef. Fissures indicate a stretching of the earth's crust, and,

therefore, probably changes in its level; but these coralislands, which have been shaken and fissured,

certainly have not been elevated, and, therefore, probably they have subsided. In the chapter on Keeling atoll,

I attempted to show by direct evidence, that the island underwent a movement of subsidence, during the

The facts stand thus;there are many large tracts of ocean, without any high land, interspersed with reefs

and islets, formed by the growth of those kinds of corals, which cannot live at great depths; and the existence

of these reefs and low islets, in such numbers and at such distant points, is quite inexplicable, excepting on

the theory, that the bases on which the reefs first became attached, slowly and successively sank beneath the

level of the sea, whilst the corals continued to grow upwards. No positive facts are opposed to this view, and

some general considerations render it probable. There is evidence of change in form, whether or not from

subsidence, on some of these coralislands; and there is evidence of subterranean disturbances beneath them.

Will then the theory, to which we have thus been led, solve the curious problem,what has given to each

A'A'Outer edge of the reef, after its upward growth during a period of subsidence.

N.B.In this, and the following woodcut, the subsidence of the land could only be represented by an

A'A'Outer edges of the barrierreef at the level of the sea. The cocoanut trees represent coralislets

B'B'The shores of the island, generally formed of low alluvial land and of coral detritus from the

C'The lagoon of the newly formed atoll. According to the scale, the depth of the lagoon and of the

Let us in imagination place within one of the subsiding areas, an island surrounded by a

"fringingreef,"that kind, which alone offers no difficulty in the explanation of its origin. Let the unbroken

lines and the oblique shading in the woodcut (No. 4) represent a vertical section through such an island; and

the horizontal shading will represent the section of the reef. Now, as the island sinks down, either a few feet

at a time or quite insensibly, we may safely infer from what we know of the conditions favourable to the

growth of coral, that the living masses bathed by the surf on the margin of the reef, will soon regain the

surface. The water, however, will encroach, little by little, on the shore, the island becoming lower and

smaller, and the space between the edge of the reef and the beach proportionately broader. A section of the

reef and island in this state, after a subsidence of several hundred feet, is given by the dotted lines:

coralislets are supposed to have been formed on the new reef, and a ship is anchored in the lagoonchannel.

This section is in every respect that of an encircling barrierreef; it is, in fact, a section taken (The section has

been made from the chart given in the "Atlas of the Voyage of the 'Coquille'." The scale is .57 of an inch to a

mile. The height of the island, according to M. Lesson, is 4,026 feet. The deepest part of the lagoonchannel

is 162 feet; its depth is exaggerated in the woodcut for the sake of clearness.) east and west through the

highest point of the encircled island of Bolabola; of which a plan is given in Plate I., Figure 5. The same

section is more clearly shown in the following woodcut (No. 5) by the unbroken lines. The width of the reef,

and its slope, both on the outer and inner side, will have been determined by the growing powers of the coral,

under the conditions (for instance the force of the breakers and of the currents) to which it has been exposed;

and the lagoonchannel will be deeper or shallower, in proportion to the growth of the delicately branched

corals within the reef, and to the accumulation of sediment, relatively, also, to the rate of subsidence and the

It is evident in this section, that a line drawn perpendicularly down from the outer edge of the new reef to the

foundation of solid rock, exceeds by as many feet as there have been feet of subsidence, that small limit of

depth at which the effective polypifers can livethe corals having grown up, as the whole sank down, from a

basis formed of other corals and their consolidated fragments. Thus the difficulty on this head, which before

As the space between the reef and the subsiding shore continued to increase in breadth and depth, and as the

injurious effects of the sediment and fresh water borne down from the land were consequently lessened, the

greater number of the channels, with which the reef in its fringing state must have been breached, especially

those which fronted the smaller streams, will have become choked up with the growth of coral: on the

windward side of the reef, where the coral grows most vigorously, the breaches will probably have first been

closed. In barrierreefs, therefore, the breaches kept open by draining the tidal waters of the lagoonchannel,

will generally be placed on the leeward side, and they will still face the mouths of the larger streams,

although removed beyond the influence of their sediment and fresh water;and this, it has been shown, is

Referring to the diagram shown above, in which the newly formed barrierreef is represented by unbroken

lines, instead of by dots as in the former woodcut, let the work of subsidence go on, and the doubly pointed

hill will form two small islands (or more, according to the number of the hills) included within one annular

reef. Let the island continue subsiding, and the coralreef will continue growing up on its own foundation,

whilst the water gains inch by inch on the land, until the last and highest pinnacle is covered, and there

remains a perfect atoll. A vertical section of this atoll is shown in the woodcut by the dotted lines;a ship is

anchored in its lagoon, but islets are not supposed yet to have been formed on the reef. The depth of the

lagoon and the width and slope of the reef, will depend on the circumstances just referred to under

barrierreefs. Any further subsidence will produce no change in the atoll, except perhaps a diminution in its

size, from the reef not growing vertically upwards; but should the currents of the sea act violently upon it, and

should the corals perish on part or on the whole of its margin, changes would result during subsidence which

will be presently noticed. I may here observe, that a bank either of rock or of hardened sediment, level with

the surface of the sea, and fringed with living coral, would (if not so small as to allow the central space to be

quickly filled up with detritus) by subsidence be converted immediately into an atoll, without passing, as in

the case of a reef fringing the shore of an island, through the intermediate form of a barrierreef. If such a

bank lay a few fathoms submerged, the simple growth of the coral (as remarked in the third chapter) without

the aid of subsidence, would produce a structure scarcely to be distinguished from a true atoll; for in all cases

the corals on the outer margin of a reef, from having space and being freely exposed to the open sea, will

grow vigorously and tend to form a continuous ring whilst the growth of the less massive kinds on the central

expanse, will be checked by the sediment formed there, and by that washed inwards by the breakers; and as

the space becomes shallower, their growth will, also, be checked by the impurities of the water, and probably

by the small amount of food brought by the enfeebled currents, in proportion to the surface of living reefs

studded with innumerable craving mouths: the subsidence of a reef based on a bank of this kind, would give

depth to its central expanse or lagoon, steepness to its flanks, and through the free growth of the coral,

symmetry to its outline:I may here repeat that the larger groups of atolls in the Pacific and Indian Oceans

If, instead of the island in the diagram, the shore of a continent fringed by a reef had subsided, a great

barrierreef, like that on the northeast coast of Australia, would have necessarily resulted; and it would have

been separated from the main land by a deepwater channel, broad in proportion to the amount of

subsidence, and to the less or greater inclination of the neighbouring coastline. The effect of the continued

subsidence of a great barrierreef of this kind, and its probable conversion into a chain of separate atolls, will

be noticed, when we discuss the apparent progressive disseverment of the larger Maldiva atolls.

We now are able to perceive that the close similarity in form, dimensions, structure, and relative position

(which latter point will hereafter be more fully noticed) between fringing and encircling barrierreefs, and

between these latter and atolls, is the necessary result of the transformation, during subsidence of the one

class into the other. On this view, the three classes of reefs ought to graduate into each other. Reefs having

intermediate character between those of the fringing and barrier classes do exist; for instance, on the

southwest coast of Madagascar, a reef extends for several miles, within which there is a broad channel from

seven to eight fathoms deep, but the sea does not deepen abruptly outside the reef. Such cases, however, are

open to some doubts, for an old fringingreef, which had extended itself a little on a basis of its own

formation, would hardly be distinguishable from a barrierreef, produced by a small amount of subsidence,

and with its lagoonchannel nearly filled up with sediment during a long stationary period. Between

barrierreefs, encircling either one lofty island or several small low ones, and atolls including a mere expanse

of water, a striking series can be shown: in proof of this, I need only refer to the first plate in this volume,

which speaks more plainly to the eye, than any description could to the ear. The authorities from which the

charts have been engraved, together with some remarks on them and descriptive of the plates, are given

above. At New Caledonia (Plate II., Figure 5.) the barrierreefs extend for 150 miles on each side of the

submarine prolongation of the island; and at their northern extremity they appear broken up and converted

into a vast atollformed reef, supporting a few low coralislets: we may imagine that we here see the effects

of subsidence actually in progress, the water always encroaching on the northern end of the island, towards

which the mountains slope down, and the reefs steadily building up their massive fabrics in the lines of their

We have as yet only considered the origin of barrierreefs and atolls in their simplest form; but there remain

some peculiarities in structure and some special cases, described in the two first chapters, to be accounted for

by our theory. These consistin the inclined ledge terminated by a wall, and sometimes succeeded by a

second ledge with a wall, round the shores of certain lagoons and lagoonchannels; a structure which cannot,

as I endeavoured to show, be explained by the simple growing powers of the corals,in the ring or

basinlike forms of the central reefs, as well as of the separate marginal portions of the northern Maldiva

atolls,in the submerged condition of the whole, or of parts of certain barrier and atollformed reefs; where

only a part is submerged, this being generally to leeward,in the apparent progressive disseverment of some

of the Maldiva atolls,in the existence of irregularly formed atolls, some being tied together by linear reefs,

and others with spurs projecting from them,and, lastly, in the structure and origin of the Great Chagos

If we suppose an atoll to subside at an extremely slow rate, it is difficult to follow out the complex results.

The living corals would grow up on the outer margin; and likewise probably in the gullies and deeper parts of

the bare surface of the annular reef; the water would encroach on the islets, but the accumulation of fresh

detritus might possibly prevent their entire submergence. After a subsidence of this very slow nature, the

surface of the annular reef sloping gently into the lagoon, would probably become united with the irregular

reefs and banks of sand, which line the shores of most lagoons. Should, however, the atoll be carried down by

a more rapid movement, the whole surface of the annular reef, where there was a foundation of solid matter,

would be favourably circumstanced for the fresh growth of coral; but as the corals grew upwards on its

exterior margin, and the waves broke heavily on this part, the increase of the massive polypifers on the inner

side would be checked from the want of water. Consequently, the exterior parts would first reach the surface,

and the new annular reef thus formed on the old one, would have its summit inclined inwards, and be

terminated by a subaqueous wall, formed by the upward growth of the coral (before being much checked),

from the inner edge of the solid parts of the old reef. The inner portion of the new reef, from not having

grown to the surface, would be covered by the waters of the lagoon. Should a subsidence of the same kind be

repeated, the corals would again grow up in a wall, from all the solid parts of the resunken reef, and,

therefore, not from within the sandy shores of the lagoon; and the inner part of the new annular reef would,

from being as before checked in its upward growth, be of less height than the exterior parts, and therefore

would not reach the surface of the lagoon. In this case the shores of the lagoon would be surrounded by two

inclined ledges, one beneath the other, and both abruptly terminated by subaqueous cliffs. (According to Mr.

Couthouy (page 26) the external reef round many atolls descends by a succession of ledges or terraces. He

attempts, I doubt whether successfully, to explain this structure somewhat in the same manner as I have

attempted, with respect to the internal ledges round the lagoons of some atolls. More facts are wanted

regarding the nature both of the interior and exterior steplike ledges: are all the ledges, or only the upper

ones, covered with living coral? If they are all covered, are the kinds different on the ledges according to the

depth? Do the interior and exterior ledges occur together in the same atolls; if so, what is their total width,

I may first observe, that the reefs within the lagoons of atolls and within lagoonchannels, would, if

favourably circumstanced, grow upwards during subsidence in the same manner as the annular rim; and,

therefore, we might expect that such lagoonreefs, when not surrounded and buried by an accumulation of

sediment more rapid than the rate of subsidence, would rise abruptly from a greater depth than that at which

the efficient polypifers can flourish: we see this well exemplified in the small abruptlysided reefs, with

which the deep lagoons of the Chagos and Southern Maldiva atolls are studded. With respect to the ring or

basinformed reefs of the Northern Maldiva atolls, it is evident, from the perfectly continuous series which

exists that the marginal rings, although wider than the exterior or bounding reef of ordinary atolls, are only

modified portions of such a reef; it is also evident that the central rings, although wider than the knolls or

reefs which commonly occur in lagoons, occupy their place. The ringlike structure has been shown to be

contingent on the breaches into the lagoon being broad and numerous, so that all the reefs which are bathed

by the waters of the lagoon are placed under nearly the same conditions with the outer coast of an atoll

standing in the open sea. Hence the exterior and living margins of these reefs must have been favourably

circumstanced for growing outwards, and increasing beyond the usual breadth; and they must likewise have

been favourably circumstanced for growing vigorously upwards, during the subsiding movements, to which

by our theory the whole archipelago has been subjected; and subsidence with this upward growth of the

margins would convert the central space of each little reef into a small lagoon. This, however, could only take

place with those reefs, which had increased to a breadth sufficient to prevent their central spaces from being

almost immediately filled up with the sand and detritus driven inwards from all sides: hence it is that few

reefs, which are less than half a mile in diameter, even in the atolls where the basinlike structure is most

strikingly exhibited, include lagoons. This remark, I may add, applies to all coralreefs wherever found. The

basinformed reefs of the Maldiva Archipelago may, in fact, be briefly described, as small atolls formed

during subsidence over the separate portions of large and broken atolls, in the same manner as these latter

were formed over the barrierreefs, which encircled the islands of a large archipelago now wholly

In the second section of the first chapter, I have shown that there are in the neighbourhood of atolls, some

deeply submerged banks, with level surfaces; that there are others, less deeply but yet wholly submerged,

having all the characters of perfect atolls, but consisting merely of dead coralrock; that there are

barrierreefs and atolls with merely a portion of their reef, generally on the leeward side, submerged; and that

such portions either retain their perfect outline, or they appear to be quite effaced, their former place being

marked only by a bank, conforming in outline with that part of the reef which remains perfect. These several

cases are, I believe, intimately related together, and can be explained by the same means. There, perhaps,

exist some submerged reefs, covered with living coral and growing upwards, but to these I do not here refer.

As we see that in those parts of the ocean, where coralreefs are most abundant, one island is fringed and

another neighbouring one is not fringed; as we see in the same archipelago, that all the reefs are more perfect

in one part of it than in another, for instance, in the southern half compared with the northern half of the

Maldiva Archipelago, and likewise on the outer coasts compared with the inner coasts of the atolls in this

same group, which are placed in a double row; as we know that the existence of the innumerable polypifers

forming a reef, depends on their sustenance, and that they are preyed on by other organic beings; and, lastly,

as we know that some inorganic causes are highly injurious to the growth of coral, it cannot be expected that

during the round of change to which earth, air, and water are exposed, the reefbuilding polypifers should

keep alive for perpetuity in any one place; and still less can this be expected, during the progressive

subsidences, perhaps at some periods more rapid than at others, to which by our theory these reefs and islands

have been subjected and are liable. It is, then, not improbable that the corals should sometimes perish either

on the whole or on part of a reef; if on part, the dead portion, after a small amount of subsidence, would still

retain its proper outline and position beneath the water. After a more prolonged subsidence, it would probably

form, owing to the accumulation of sediment, only the margin of a flat bank, marking the limits of the former

lagoon. Such dead portions of reef would generally lie on the leeward side (Mr. Lyell, in the first edition of

his "Principles of Geology," offered a somewhat different explanation of this structure. He supposes that

there has been subsidence; but he was not aware that the submerged portions of reef were in most cases, if not

in all, dead; and he attributes the difference in height in the two sides of most atolls, chiefly to the greater

accumulation of detritus to windward than to leeward. But as matter is accumulated only on the backward

part of the reef, the front part would remain of the same height on both sides. I may here observe that in most

cases (for instance, at Peros Banhos, the Gambier group and the Great Chagos Bank), and I suspect in all

cases, the dead and submerged portions do not blend or slope into the living and perfect parts, but are

separated from them by an abrupt line. In some instances small patches of living reef rise to the surface from

the middle of the submerged and dead parts.), for the impure water and fine sediment would more easily flow

out from the lagoon over this side of the reef, where the force of the breakers is less than to windward; and

therefore the corals would be less vigorous on this side, and be less able to resist any destroying agent. It is

likewise owing to this same cause, that reefs are more frequently breached to leeward by narrow channels,

serving as by shipchannels, than to windward. If the corals perished entirely, or on the greater part of the

circumference of an atoll, an atollshaped bank of dead rock, more or less entirely submerged, would be

produced; and further subsidence, together with the accumulation of sediment, would often obliterate its

In the Chagos group of atolls, within an area of 160 miles by 60, there are two atollformed banks of dead

rock (besides another very imperfect one), entirely submerged; a third, with merely two or three very small

pieces of living reef rising to the surface; and a fourth, namely, Peros Banhos (Plate I., Figure 9), with a

portion nine miles in length dead and submerged. As by our theory this area has subsided, and as there is

nothing improbable in the death, either from changes in the state of the surrounding sea or from the

subsidence being great or sudden, of the corals on the whole, or on portions of some of the atolls, the case of

the Chagos group presents no difficulty. So far indeed are any of the abovementioned cases of submerged

reefs from being inexplicable, that their occurrence might have been anticipated on our theory, and as fresh

atolls are supposed to be in progressive formation by the subsidence of encircling barrierreefs, a weighty

objection, namely that the number of atolls must be increasing infinitely, might even have been raised, if

proofs of the occasional destruction and loss of atolls could not have been adduced.

The apparent progressive disseverment in the Maldiva Archipelago of large atolls into smaller ones, is, in

many respects, an important consideration, and requires an explanation. The graduated series which marks, as

I believe, this process, can be observed only in the northern half of the group, where the atolls have

exceedingly imperfect margins, consisting of detached basinformed reefs. The currents of the sea flow

across these atolls, as I am informed by Captain Moresby, with considerable force, and drift the sediment

from side to side during the monsoons, transporting much of it seaward; yet the currents sweep with greater

force round their flanks. It is historically known that these atolls have long existed in their present state; and

we can believe, that even during a very slow subsidence they might thus remain, the central expanse being

kept at nearly its original depth by the accumulation of sediment. But in the action of such nicely balanced

forces during a progressive subsidence (like that, to which by our theory this archipelago has been subjected),

it would be strange if the currents of the sea should never make a direct passage across some one of the atolls,

through the many wide breaches in their margins. If this were once effected, a deepwater channel would

soon be formed by the removal of the finer sediment, and the check to its further accumulation; and the sides

of the channel would be worn into a slope like that on the outer coasts, which are exposed to the same force

of the currents. In fact, a channel precisely like that bifurcating one which divides Mahlos Mahdoo (Plate II.,

Figure 4.), would almost necessarily be formed. The scattered reefs situated near the borders of the new

oceanchannel, from being favourably placed for the growth of coral, would, by their extension, tend to

produce fresh margins to the dissevered portions; such a tendency is very evident (as may be seen in the large

published chart) in the elongated reefs on the borders of the two channels intersecting Mahlos Mahdoo. Such

channels would become deeper with continued subsidence, and probably from the reefs not growing up

perpendicularly, somewhat broader. In this case, and more especially if the channels had been formed

originally of considerable breadth, the dissevered portions would become perfect and distinct atolls, like Ari

and Ross atolls (Plate II., Figure 6), or like the two Nillandoo atolls, which must be considered as distinct,

although related in form and position, and separated from each other by channels, which though deep have

been sounded. Further subsidence would render such channels unfathomable, and the dissevered portions

would then resemble Phaleedoo and Moluque atolls, or Mahlos Mahdoo and Horsburgh atolls (Plate II.,

Figure 4), which are related to each other in no respect except in proximity and position. Hence, on the theory

of subsidence, the disseverment of large atolls, which have imperfect margins (for otherwise their

disseverment would be scarcely possible), and which are exposed to strong currents, is far from being an

improbable event; and the several stages, from close relation to entire isolation in the atolls of the Maldiva

We might go even further, and assert as not improbable, that the first formation of the Maldiva Archipelago

was due to a barrierreef, of nearly the same dimensions with that of New Caledonia (Plate II., Figure 5), for

if, in imagination, we complete the subsidence of that great island, we might anticipate from the present

broken condition of the northern portion of the reef, and from the almost entire absence of reefs on the

eastern coast, that the barrierreef after repeated subsidences, would become during its upward growth

separated into distinct portions; and these portions would tend to assume an atolllike structure, from the

coral growing with vigour round their entire circumferences, when freely exposed to an open sea. As we have

some large islands partly submerged with barrierreefs marking their former limits, such as New Caledonia,

so our theory makes it probable that there should be other large islands wholly submerged; and these, we may

now infer, would be surmounted, not by one enormous atoll, but by several large elongated ones, like the

atolls in the Maldiva group; and these again, during long periods of subsidence, would sometimes become

dissevered into smaller atolls. I may add, that both in the Marshall and Caroline Archipelagoes, there are

atolls standing close together, which have an evident relationship in form: we may suppose, in such cases,

either that two or more encircled islands originally stood close together, and afforded bases for two or more

atolls, or that one atoll has been dissevered. From the position, as well as form, of three atolls in the Caroline

Archipelago (the Namourrek and Elato group), which are placed in an irregular circle, I am strongly tempted

to believe that they have originated by the process of disseverment. (The same remark is, perhaps, applicable

to the islands of Ollap, Fanadik, and Tamatam in the Caroline Archipelago, of which charts are given in the

atlas of Duperrey's voyage: a line drawn through the linear reefs and lagoons of these three islands forms a

semicircle. Consult also, the atlas of Lutke's voyage; and for the Marshall group that of Kotzebue; for the

Gilbert group consult the atlas of Duperrey's voyage. Most of the points here referred to may, however, be

In the Marshall group, Musquillo atoll consists of two loops united in one point; and Menchikoff atoll is

formed of three loops, two of which (as may be seen in Figure 3, Plate II.) are connected by a mere

ribbonshaped reef, and the three together are sixty miles in length. In the Gilbert group some of the atolls

have narrow strips of reef, like spurs, projecting from them. There occur also in parts of the open sea, a few

linear and straight reefs, standing by themselves; and likewise some few reefs in the form of crescents, with

their extremities more or less curled inwards. Now, the upward growth of a barrierreef which fronted only

one side of an island, or one side of an elongated island with its extremities (of which cases exist), would

produce after the complete subsidence of the land, mere strips or crescent or hookformed reefs: if the island

thus partially fronted became divided during subsidence into two or more islands, these islands would be

united together by linear reefs; and from the further growth of the coral along their shores together with

subsidence, reefs of various forms might ultimately be produced, either atolls united together by linear reefs,

or atolls with spurs projecting from them. Some, however, of the more simple forms above specified, might,

as we have seen, be equally well produced by the coral perishing during subsidence on part of the

circumference of an atoll, whilst on the other parts it continued to grow up till it reached the surface.

I have already shown that the submerged condition of the Great Chagos Bank (Plate II., Figure 1, with its

section Figure 2), and of some other banks in the Chagos group, may in all probability be attributed to the

coral having perished before or during the movements of subsidence, to which this whole area by our theory

has been subjected. The external rim or upper ledge (shaded in the chart), consists of dead coralrock thinly

covered with sand; it lies at an average depth of between five and eight fathoms, and perfectly resembles in

form the annular reef of an atoll. The banks of the second level, the boundaries of which are marked by

dotted lines in the chart, lie from about fifteen to twenty fathoms beneath the surface; they are several miles

broad, and terminate in a very steep slope round the central expanse. This central expanse I have already

described, as consisting of a level muddy flat between thirty and forty fathoms deep. The banks of the second

level, might at first sight be thought analogous to the internal steplike ledge of coralrock which borders the

lagoons of some atolls, but their much greater width, and their being formed of sand, are points of essential

difference. On the eastern side of the atoll some of the banks are linear and parallel, resembling islets in a

great river, and pointed directly towards a great breach on the opposite side of the atoll; these are best seen in

the large published chart. I inferred from this circumstance, that strong currents sometimes set directly across

this vast bank; and I have since heard from Captain Moresby that this is the case. I observed, also, that the

channels or breaches through the rim, were all of the same depth as the central lagoonlike space into which

they lead; whereas the channels into the other atolls of the Chagos group, and as I believe into most other

large atolls, are not nearly as deep as their lagoons: for instance at Peros Banhos, the channels are only of the

same depth, namely between ten and twenty fathoms, as the bottom of the lagoon for a space about a mile

and a half in width round its shores, whilst the central expanse of the lagoon is from thirtyfive to forty

fathoms deep. Now, if an atoll during a gradual subsidence once became entirely submerged, like the Great

Chagos Bank, and therefore no longer exposed to the surf, very little sediment could be formed from it; and

consequently the channels leading into the lagoon from not being filled up with drifted sand and coral

detritus, would continue increasing in depth, as the whole sank down. In this case, we might expect that the

currents of the open sea, instead of any longer sweeping round the submarine flanks, would flow directly

through the breaches across the lagoon, removing in their course the finer sediment, and preventing its further

accumulation. We should then have the submerged reef forming an external and upper rim of rock, and

beneath this portion of the sandy bottom of the old lagoon, intersected by deepwater channels or breaches,

and thus formed into separate marginal banks; and these would be cut off by steep slopes, overhanging the

By these means, I have scarcely any doubt that the Great Chagos Bank has originated,a structure which at

first appeared to me far more anomalous than any I had met with. The process of formation is nearly the same

with that, by which Mahlos Mahdoo had been trisected; but in the Chagos Bank the channels of the oceanic

currents entering at several different quarters, have united in a central space.

This great atollformed bank appears to be in an early stage of disseverment; should the work of subsidence

go on, from the submerged and dead condition of the whole reef, and the imperfection of the southeast

quarter a mere wreck would probably be left. The Pitt's Bank, situated not far southward, appears to be

precisely in this state; it consists of a moderately level, oblong bank of sand, lying from 10 to 20 fathoms

beneath the surface, with two sides protected by a narrow ledge of rock which is submerged between 5 and 8

fathoms. A little further south, at about the same distance as the southern rim of the Great Chagos Bank is

from the northern rim, there are two other small banks with from 10 to 20 fathoms on them; and not far

eastward soundings were struck on a sandy bottom, with between 110 and 145 fathoms. The northern portion

with its ledgelike margin, closely resembles any one segment of the Great Chagos Bank, between two of the

deepwater channels, and the scattered banks, southward appear to be the last wrecks of less perfect portions.

I have examined with care the charts of the Indian and Pacific Oceans, and have now brought before the

reader all the examples, which I have met with, of reefs differing from the type of the class to which they

belong; and I think it has been satisfactorily shown, that they are all included in our theory, modified by

occasional accidents which might have been anticipated as probable. In this course we have seen, that in the

lapse of ages encircling barrierreefs are occasionally converted into atolls, the name of atoll being properly

applicable, at the moment when the last pinnacle of encircled land sinks beneath the surface of the sea. We

have, also, seen that large atolls during the progressive subsidence of the areas in which they stand,

sometimes become dissevered into smaller ones; at other times, the reefbuilding polypifers having entirely

perished, atolls are converted into atollformed banks of dead rock; and these again through further

subsidence and the accumulation of sediment modified by the force of the oceanic currents, pass into level

banks with scarcely any distinguishing character. Thus may the history of an atoll be followed from its first

origin, through the occasional accidents of its existence, to its destruction and final obliteration.

The vast amount of subsidence, both horizontally or in area, and vertically or in depth, necessary to have

submerged every mountain, even the highest, throughout the immense spaces of ocean interspersed with

atolls, will probably strike most people as a formidable objection to my theory. But as continents, as large as

the spaces supposed to have subsided, have been raised above the level of the sea,as whole regions are

now rising, for instance, in Scandinavia and South America,and as no reason can be assigned, why

subsidences should not have occurred in some parts of the earth's crust on as great a scale both in extent and

amount as those of elevation, objections of this nature strike me as of little force. The remarkable point is that

movements to such an extent should have taken place within a period, during which the polypifers have

continued adding matter on and above the same reefs. Another and less obvious objection to the theory will

perhaps be advanced from the circumstance, of the lagoons within atolls and within barrierreefs never

having become in any one instance during prolonged subsidences of a greater depth than sixty fathoms, and

seldom more than forty fathoms; but we already admit, if the theory be worth considering, that the rate of

subsidence has not exceeded that of the upward growth of the coral on the exterior margin; we are, therefore,

only further required to admit, that the subsidence has not exceeded in rate the filling up of the interior spaces

by the growth of the corals living there, and by the accumulation of sediment. As this filling up must take

place very slowly within barrierreefs lying far from the land, and within atolls which are of large

dimensions and which have open lagoons with very few reefs, we are led to conclude that the subsidence thus

counterbalanced, must have been slow in an extraordinary degree; a conclusion which accords with our only

means, namely, with what is known of the rate and manner of recent elevatory movements, of judging by

In this chapter it has, I think, been shown, that the theory of subsidence, which we were compelled to receive

from the necessity of giving to the corals, in certain large areas, foundations at the requisite depth, explains

both the normal structure and the less regular forms of those two great classes of reefs, which have justly

excited the astonishment of all persons who have sailed through the Pacific and Indian Oceans. But further to

test the truth of the theory, a crowd of questions will occur to the reader: Do the different kinds of reefs,

which have been produced by the same kind of movement, generally lie within the same areas? What is their

relation of form and position,for instance, do adjoining groups of atolls, and the separate atolls in these

groups, bear the same relation to each other which islands do in common archipelagoes? Have we reason to

believe, that where there are fringingreefs, there has not lately been subsidence; or, for it is almost our only

way of ascertaining this point, are there frequently proofs of recent elevation? Can we by this means account

for the presence of certain classes of reefs in some large areas, and their entire absence in others? Do the

areas which have subsided, as indicated by the presence of atolls and barrierreefs, and the areas which have

remained stationary or have been upraised, as shown by fringingreefs, bear any determinate relation to each

other; and are the dimensions of these areas such as harmonise with the greatness of the subterranean

changes, which, it must be supposed, have lately taken place beneath them? Is there any connection between

the movements thus indicated, and recent volcanic action? All these questions ought to receive answers in

accordance with the theory; and if this can be satisfactorily shown, not only is the theory confirmed, but as

deductions, the answers are in themselves important. Under this latter point of view, these questions will be

(I may take this opportunity of briefly considering the appearances, which would probably be presented by a

vertical and deep section across a coral formation (referring chiefly to an atoll), formed by the upward growth

of coral during successive subsidences. This is a subject worthy of attention, as a means of comparison with

ancient coralstrata. The circumferential parts would consist of massive species, in a vertical position, with

their interstices filled up with detritus; but this would be the part most subject to subsequent denudation and

removal. It is useless to speculate how large a portion of the exterior annular reef would consist of upright

coral, and how much of fragmentary rock, for this would depend on many contingencies,such as on the

rate of subsidence, occasionally allowing a fresh growth of coral to cover the whole surface, and on the

breakers having force sufficient to throw fragments over this same space. The conglomerate which composes

the base of the islets, would (if not removed by denudation together with the exterior reef on which it rests)

be conspicuous from the size of the fragments,the different degrees in which they have been

rounded,the presence of fragments of conglomerate torn up, rounded, and recemented,and from the

oblique stratification. The corals which lived in the lagoonreefs at each successive level, would be preserved

upright, and they would consist of many kinds, generally much branched. In this part, however, a very large

proportion of the rock (and in some cases nearly all of it) would be formed of sedimentary matter, either in an

excessively fine, or in a moderately coarse state, and with the particles almost blended together. The

conglomerate which was formed of rounded pieces of the branched corals, on the shores of the lagoon, would

differ from that formed on the islets and derived from the outer coast; yet both might have accumulated very

near each other. I have seen a conglomerate limestone from Devonshire like a conglomerate now forming on

the shores of the Maldiva atolls. The stratification taken as a whole, would be horizontal; but the

conglomerate beds resting on the exterior reef, and the beds of sandstone on the shores of the lagoon (and no

doubt on the external flanks) would probably be divided (as at Keeling atoll and at Mauritius) by numerous

layers dipping at considerable angles in different directions. The calcareous sandstone and coralrock would

almost necessarily contain innumerable shells, echini, and the bones of fish, turtle, and perhaps of birds;

possibly, also, the bones of small saurians, as these animals find their way to the islands far remote from any

continent. The large shells of some species of Tridacna would be found vertically imbedded in the solid rock,

in the position in which they lived. We might expect also to find a mixture of the remains of pelagic and

littoral animals in the strata formed in the lagoon, for pumice and the seeds of plants are floated from distant

countries into the lagoons of many atolls: on the outer coast of Keeling atoll, near the mouth of the lagoon,

the case of a pelagic Pteropodous animal was brought up on the arming of the sounding lead. All the loose

blocks of coral on Keeling atoll were burrowed by vermiform animals; and as every cavity, no doubt,

ultimately becomes filled with spathose limestone, slabs of the rock taken from a considerable depth, would,

if polished, probably exhibit the excavations of such burrowing animals. The conglomerate and finegrained

beds of coralrock would be hard, sonorous, white and composed of nearly pure calcareous matter; in some

few parts, judging from the specimens at Keeling atoll, they would probably contain a small quantity of iron.

Floating pumice and scoriae, and occasionally stones transported in the root of trees (see my "Journal of

Researches," page 549) appear the only sources, through which foreign matter is brought to coralformations

standing in the open ocean. The area over which sediment is transported from coralreefs must be

considerable: Captain Moresby informs me that during the change of monsoons the sea is discoloured to a

considerable distance off the Maldiva and Chagos atolls. The sediment of fringing and barrier coralreefs

must be mingled with the mud, which is brought down from the land, and is transported seaward through the

breaches, which occur in front of almost every valley. If the atolls of the larger archipelagoes were upraised,

the bed of the ocean being converted into land, they would form flattopped mountains, varying in diameter

from a few miles (the smallest atolls being worn away) to sixty miles; and from being horizontally stratified

and of similar composition, they would, as Mr. Lyell has remarked, falsely appear as if they had originally

been united into one vast continuous mass. Such great strata of coralrock would rarely be associated with

erupted volcanic matter, for this could only take place, as may be inferred from what follows in the next

chapter, when the area, in which they were situated, commenced to rise, or at least ceased to subside. During

the enormous period necessary to effect an elevation of the kind just alluded to, the surface would necessarily

be denuded to a great thickness; hence it is highly improbable that any fringingreef, or even any

barrierreef, at least of those encircling small islands, would be preserved. From this same cause, the strata

which were formed within the lagoons of atolls and lagoonchannels of barrierreefs, and which must consist

in a large part of sedimentary matter, would more often be preserved to future ages, than the exterior solid

reef, composed of massive corals in an upright position; although it is on this exterior part that the present

The principles, on which this map was coloured, are explained in the beginning of Chapter VI.; and the

authorities for each particular spot are detailed in the Appendix to "Coral Reefs." The names not printed in

Description of the coloured map.Proximity of atolls and barrierreefs. Relation in form and position of

atolls with ordinary islands.Direct evidence of subsidence difficult to be detected.Proofs of recent

elevation where fringingreefs occur.Oscillations of level.Absence of active volcanoes in the areas of

subsidence.Immensity of the areas which have been elevated and have subsided.Their relation to the

present distribution of the land.Areas of subsidence elongated, their intersection and alternation with those

It will be convenient to give here a short account of the appended map (Plate III.) [Inasmuch as the coloured

map would have proved too costly to be given in this series, the indications of colour have been replaced by

numbers referring to the dotted groups of reefs, etc. The author's original wording, however, is retained in

full, as it will be easy to refer to the map by the numbers, and thus the flow of the narrative is undisturbed.]: a

fuller one, with the data for colouring each spot, is reserved for the Appendix; and every place there referred

to may be found in the Index. A larger chart would have been desirable; but, small as the adjoined one is, it is

the result of many months' labour. I have consulted, as far as I was able, every original voyage and map; and

the colours were first laid down on charts on a larger scale. The same blue colour, with merely a difference in

the depth of tint, is used for atolls or lagoonislands, and barrierreefs, for we have seen, that as far as the

actual coralformation is concerned, they have no distinguishing character. Fringingreefs have been

coloured red, for between them on the one hand, and barrierreefs and atolls on the other, there is an

important distinction with respect to the depth beneath the surface, at which we are compelled to believe their

foundations lie. The two distinct colours, therefore, mark two great types of structure.

The DARK BLUE COLOUR [represented by (3) in our plate] represents atolls and submerged annular reefs,

with deep water in their centres. I have coloured as atolls, a few low and small coralislands, without

lagoons; but this has been done only when it clearly appeared that they originally contained lagoons, since

filled up with sediment: when there were not good grounds for this belief, they have been left uncoloured.

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 59

The PALE BLUE COLOUR [represented by (2)] represents barrierreefs. The most obvious character of

reefs of this class is the broad and deepwater moat within the reef: but this, like the lagoons of small atolls,

is liable to become filled up with detritus and with reefs of delicately branched corals: when, therefore, a reef

round the entire circumference of an island extends very far into a profoundly deep sea, so that it can hardly

be confounded with a fringingreef which must rest on a foundation of rock within a small depth, it has been

coloured pale blue, although it does not include a deepwater moat: but this has only been done rarely, and

The RED COLOUR (4) represents reefs fringing the land quite closely where the sea is deep, and where the

bottom is gently inclined extending to a moderate distance from it, but not having a deepwater moat or

lagoonlike space parallel to the shore. It must be remembered that fringingreefs are frequently

BREACHED in front of rivers and valleys by deepish channels, where mud has been deposited. A space of

thirty miles in width has been coloured round or in front of the reefs of each class, in order that the colours

The VERMILLION SPOTS, and streaks (1) represent volcanoes now in action, or historically known to have

been so. They are chiefly laid down from Von Buch's work on the Canary Islands; and my reasons for

(I have also made considerable use of the geological part of Berghaus' "Physical Atlas." Beginning at the

eastern side of the Pacific, I have added to the number of the volcanoes in the southern part of the Cordillera,

and have coloured Juan Fernandez according to observations collected during the voyage of the "Beagle"

("Geological Transactions," volume v., page 601.) I have added a volcano to Albemarle Island, one of the

Galapagos Archipelago (the author's "Journal of Researches," page 457). In the Sandwich group there are no

active volcanoes, except at Hawaii; but the Rev. W. Ellis informs me, there are streams of lava apparently

modern on Maui, having a very recent appearance, which can be traced to the craters whence they flowed.

The same gentleman informs me, that there is no reason to believe that any active volcano exists in the

Society Archipelago; nor are there any known in the Samoa or Navigator group, although some of the

streams of lava and craters there appear recent. In the Friendly group, the Rev. J. Williams says ("Narrative of

Missionary Enterprise," page 29) that Toofoa and Proby Islands are active volcanoes. I infer from Hamilton's

"Voyage in the 'Pandora'" (Page 95), that Proby Island is synonymous with Onouafou, but I have not

ventured to colour it. There can be no doubt respecting Toofoa, and Captain Edwards (Von Buch, page 386)

found the lava of recent eruption at Amargura still smoking. Berghaus marks four active volcanoes actually

within the Friendly group; but I do not know on what authority: I may mention that Maurelle describes Latte

as having a burntup appearance: I have marked only Toofoa and Amargura. South of the New Hebrides lies

Matthews Rock, which is drawn and described as an active crater in the "Voyage of the 'Astrolabe'." Between

it and the volcano on the eastern side of New Zealand, lies Brimstone Island, which from the high

temperature of the water in the crater, may be ranked as active (Berghaus "Vorbemerk," II Lief. S. 56). Malte

Brun, volume xii., page 231, says that there is a volcano near port St. Vincent in New Caledonia. I believe

this to be an error, arising from a smoke seen on the OPPOSITE coast by Cook ("Second Voyage," volume

ii., page 23) which smoke went out at night. The Mariana Islands, especially the northern ones, contain many

craters (see Freycinet's "Hydrog. Descript.") which are not active. Von Buch, however, states (page 462) on

the authority of La Peyrouse, that there are no less than seven volcanoes between these islands and Japan.

Gemelli Creri (Churchill's "Collect." volume iv., page 458), says there are two active volcanoes in latitude 23

deg 30', and in latitude 24 deg: but I have not coloured them. From the statements in Beechey's "Voyage"

(page 518, 4to edition) I have coloured one in the northern part of the Bonin group. M. S. Julien has clearly

made out from Chinese manuscripts not very ancient ("Comptes Rendus," 1840, page 832), that there are two

active volcanoes on the eastern side of Formosa. In Torres Straits, on Cap Island (9 deg 48' S., 142 deg 39' E.)

a volcano was seen burning with great violence in 1793 by Captain Bampton (see Introduction to Flinders'

"Voyage," page 41). Mr. M'Clelland (Report of Committee for investigating Coal in India, page 39) has

shown that the volcanic band passing through Barren Island must be extended northwards. It appears by an

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 60

old chart, that Cheduba was once an active volcano (see also "Silliman's North American Journal", volume

xxxviii., page 385). In Berghaus' "Physical Atlas," 1840, No. 7 of Geological Part, a volcano on the coast of

Pondicherry is said to have burst forth in 1757. Ordinaire ("Hist. Nat. des Volcans," page 218) says that there

is one at the mouth of the Persian Gulf, but I have not coloured it, as he gives no particulars. A volcano in

Amsterdam, or St. Paul's, in the southern part of the Indian Ocean, has been seen ("Naut. Mag." 1838, page

842) in action. Dr. J. Allan, of Forres, informs me in a letter, that when he was at Joanna, he saw at night

flames apparently volcanic, issuing from the chief Comoro Island, and that the Arabs assured him that they

were volcanic, adding that the volcano burned more during the wet season. I have marked this as a volcano,

though with some hesitation, on account of the possibility of the flame arising from gaseous sources.)

The uncoloured coasts consist, first and chiefly, of those, where there are no coralreefs, or such small

portions as to be quite insignificant. Secondly, of those coasts where there are reefs, but where the sea is very

shallow, for in this case the reefs generally lie far from the land, and become very irregular, in their forms:

where they have not become irregular, they have been coloured. thirdly, if I had the means of ascertaining the

fact, I should not colour a reef merely coating the edges of a submarine crater, or of a level submerged bank;

for such superficial formations differ essentially, even when not in external appearance, from reefs whose

foundations as well as superficies have been wholly formed by the growth of coral. Fourthly, in the Red Sea,

and within some parts of the East Indian Archipelago (if the imperfect charts of the latter can be trusted),

there are many scattered reefs, of small size, represented in the chart by mere dots, which rise out of deep

water: these cannot be arranged under either of the three classes: in the Red Sea, however, some of these little

reefs, from their position, seem once to have formed parts of a continuous barrier. There exist, also, scattered

in the open ocean, some linear and irregularly formed strips of coralreef, which, as shown in the last

chapter, are probably allied in their origin to atolls; but as they do not belong to that class, they have not been

coloured; they are very few in number and of insignificant dimensions. Lastly, some reefs are left uncoloured

from the want of information respecting them, and some because they are of an intermediate structure

between the barrier and fringing classes. The value of the map is lessened, in proportion to the number of

reefs which I have been obliged to leave uncoloured, although, in a theoretical point of view, few of them

present any great difficulty: but their number is not very great, as will be found by comparing the map with

the statements in the Appendix. I have experienced more difficulty in colouring fringingreefs than in

colouring barrierreefs, as the former, from their much less dimensions, have less attracted the attention of

navigators. As I have had to seek my information from all kinds of sources, and often from indirect ones, I do

not venture to hope that the map is free from many errors. Nevertheless, I trust it will give an approximately

correct view of the general distribution of the coralreefs over the whole world (with the exception of some

fringingreefs on the coast of Brazil, not included within the limits of the map), and of their arrangement into

the three great classes, which, though necessarily very imperfect from the nature of the objects classified,

have been adopted by most voyagers. I may further remark, that the dark blue colour represents land entirely

composed of coralrock; the pale blue, land with a wide and thick border of coralrock; and the red, a mere

Looking now at the map under the theoretical point of view indicated in the last chapter, the two blue tints

signify that the foundations of the reefs thus coloured have subsided to a considerable amount, at a slower

rate than that of the upward growth of the corals, and that probably in many cases they are still subsiding. The

red signifies that the shores which support fringingreefs have not subsided (at least to any considerable

amount, for the effects of a subsidence on a small scale would in no case be distinguishable); but that they

have remained nearly stationary since the period when they first became fringed by reefs; or that they are

now rising or have been upraised, with new lines of reefs successively formed on them: these latter

alternatives are obviously implied, as newly formed lines of shore, after elevations of the land, would be in

the same state with respect to the growth of fringingreefs, as stationary coasts. If during the prolonged

subsidence of a shore, coralreefs grew for the first time on it, or if an old barrierreef were destroyed and

submerged, and new reefs became attached to the land, these would necessarily at first belong to the fringing

class, and, therefore, be coloured red, although the coast was sinking: but I have no reason to believe, that

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 61

from this source of error, any coast has been coloured wrongly with respect to movement indicated. Well

characterised atolls and encircling barrierreefs, where several occur in a group, or a single barrierreef if of

large dimensions, leave scarcely any doubt on the mind respecting the movement by which they have been

produced; and even a small amount of subsequent elevation is soon betrayed. The evidence from a single

atoll or a single encircling barrierreef, must be received with some caution, for the former may possibly be

based upon a submerged crater or bank, and the latter on a submerged margin of sediment, or of worndown

rock. From these remarks we may with greater certainty infer that the spaces, especially the larger ones,

tinted blue in the map, have subsided, than that the red spaces have remained stationary, or have been

Having made these preliminary remarks, I will consider first how far the grouping of the different kinds of

coralislands and reefs is corroborative of the truth of the theory. A glance at the map shows that the reefs,

coloured blue and red, produced under widely different conditions, are not indiscriminately mixed together.

Atolls and barrierreefs, on the other hand, as may be seen by the two blue tints, generally lie near each

other; and this would be the natural result of both having been produced during the subsidence of the areas in

which they stand. Thus, the largest group of encircled islands is that of the Society Archipelago; and these

islands are surrounded by atolls, and only separated by a narrow space from the large group of Low atolls. In

the midst of the Caroline atolls, there are three fine encircled islands. The northern point of the barrierreef of

New Caledonia seems itself, as before remarked, to form a complete large atoll. The great Australian barrier

is described as including both atolls and small encircled islands. Captain King (Sailing directions, appended

to volume ii. of his "Surveying Voyage to Australia.") mentions many atollformed and encircling

coralreefs, some of which lie within the barrier, and others may be said (for instance between latitude 16

deg and 13 deg) to form part of it. Flinders ("Voyage to Terra Australis," volume ii. page 336.) has described

an atollformed reef in latitude 10 deg, seven miles long and from one to three broad, resembling a boot in

shape, with apparently very deep water within. Eight miles westward of this, and forming part of the barrier,

lie the Murray Islands, which are high and are encircled. In the Corallian Sea, between the two great barriers

of Australia and New Caledonia, there are many low islets and coralreefs, some of which are annular, or

horseshoe shaped. Observing the smallness of the scale of the map, the parallels of latitude being nine

hundred miles apart, we see that none of the large groups of reefs and islands supposed to have been

produced by longcontinued subsidence, lie near extensive lines of coast coloured red, which are supposed to

have remained stationary since the growth of their reefs, or to have been upraised and new lines of reefs

formed on them. Where the red and blue circles do occur near each other, I am able, in several instances, to

show that there have been oscillations of level, subsidence having preceded the elevation of the red spots; and

elevation having preceded the subsidence of the blue spots: and in this case the juxtaposition of reefs

belonging to the two great types of structure is little surprising. We may, therefore, conclude that the

proximity in the same areas of the two classes of reefs, which owe their origin to the subsidence of the earth's

crust, and their separation from those formed during its stationary or uprising condition, holds good to the full

As groups of atolls have originated in the upward growth, at each fresh sinking of the land, of those reefs

which primarily fringed the shores of one great island, or of several smaller ones; so we might expect that

these rings of coralrock, like so many rude outline charts, will still retain some traces of the general form, or

at least general range, of the land, round which they were first modelled. That this is the case with the atolls

in the Southern Pacific as far as their range is concerned, seems highly probable, when we observe that the

three principal groups are directed in northwest and southeast lines, and that nearly all the land in the S.

Pacific ranges in this same direction; namely, N. Western Australia, New Caledonia, the northern half of New

Zealand, the New Hebrides, Saloman, Navigator, Society, Marquesas, and Austral archipelagoes: in the

Northern Pacific, the Caroline atolls abut against the northwest line of the Marshall atolls, much in the same

manner as the east and west line of islands from Ceram to New Britain do on New Ireland: in the Indian

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 62

Ocean the Laccadive and Maldiva atolls extend nearly parallel to the western and mountainous coast of India.

In most respects, there is a perfect resemblance with ordinary islands in the grouping of atolls and in their

form: thus the outline of all the larger groups is elongated; and the greater number of the individual atolls are

elongated in the same direction with the group, in which they stand. The Chagos group is less elongated than

is usual with other groups, and the individual atolls in it are likewise but little elongated; this is strikingly

seen by comparing them with the neighbouring Maldiva atolls. In the Marshall and Maldiva archipelagoes,

the atolls are ranged in two parallel lines, like the mountains in a great double mountainchain. Some of the

atolls, in the larger archipelagoes, stand so near to each other, and have such an evident relationship in form,

that they compose little subgroups: in the Caroline Archipelago, one such subgroup consists of Pouynipete,

a lofty island encircled by a barrierreef, and separated by a channel only four miles and a half wide from

Andeema atoll, with a second atoll a little further off. In all these respects an examination of a series of charts

With respect to subsidence, I have shown in the last chapter, that we cannot expect to obtain in countries

inhabited only by semicivilised races, demonstrative proofs of a movement, which invariably tends to

conceal its own evidence. But on the coralislands supposed to have been produced by subsidence, we have

proofs of changes in their external appearanceof a round of decay and renovationof the last vestiges of

land on someof its first commencement on others: we hear of storms desolating them to the astonishment

of their inhabitants: we know by the great fissures with which some of them are traversed, and by the

earthquakes felt under others, that subterranean disturbances of some kind are in progress. These facts, if not

directly connected with subsidence, as I believe they are, at least show how difficult it would be to discover

proofs of such movement by ordinary means. At Keeling atoll, however, I have described some appearances,

which seem directly to show that subsidence did take place there during the late earthquakes. Vanikoro,

according to Chevalier Dillon (See Captain Dillon's "Voyage in search of La Peyrouse." M. Cordier in his

"Report on the Voyage of the 'Astrolabe'" (page cxi., volume i.), speaking of Vanikoro, says the shores are

surrounded by reefs of madrepore, "qu'on assure etre de formation toutafait moderne." I have in vain

endeavoured to learn some further particulars about this remarkable passage. I may here add, that according

to our theory, the island of Pouynipete (Plate I., Figure 7), in the Caroline Archipelago, being encircled by a

barrierreef, must have subsided. In the "New S. Wales Lit. Advert." February 1835 (which I have seen

through the favour of Dr. Lloghtsky), there is an account of this island (subsequently confirmed by Mr.

Campbell), in which it is said, "At the N.E. end, at a place called Tamen, there are ruins of a town, NOW

ONLY accessible by boats, the waves REACHING TO THE STEPS OF The HOUSES." Judging from this

passage, one would be tempted to conclude that the island must have subsided, since these houses were built.

I may, also, here append a statement in Malte Brun (volume ix., page 775, given without any authority), that

the sea gains in an extraordinary manner on the coast of Cochin China, which lies in front and near the

subsiding coralreefs in the China Sea: as the coast is granitic, and not alluvial, it is scarcely possible that the

encroachment of the sea can be owing to the washing away of the land; and if so, it must be due to

subsidence.), is often violently shaken by earthquakes, and there, the unusual depth of the channel between

the shore and the reef,the almost entire absence of islets on the reef, its walllike structure on the inner

side, and the small quantity of low alluvial land at the foot of the mountains, all seem to show that this island

has not remained long at its present level, with the lagoonchannel subjected to the accumulation of

sediment, and the reef to the wear and tear of the breakers. At the Society Archipelago, on the other hand,

where a slight tremor is only rarely felt, the shoaliness of the lagoonchannels round some of the islands, the

number of islets formed on the reefs of others, and the broad belt of low land at the foot of the mountains,

indicate that, although there must have been great subsidence to have produced the barrierreefs, there has

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 63

(Mr. Couthouy states ("Remarks," page 44) that at Tahiti and Eimeo the space between the reef and the shore

has been nearly filled up by the extension of those coralreefs, which within most barrierreefs merely fringe

the land. From this circumstance, he arrives at the same conclusion as I have done, that the Society Islands

since their subsidence, have remained stationary during a long period; but he further believes that they have

recently commenced rising, as well as the whole area of the Low Archipelago. He does not give any detailed

proofs regarding the elevation of the Society Islands, but I shall refer to this subject in another part of this

chapter. Before making some further comments, I may observe how satisfactory it is to me, to find Mr.

Couthouy affirming, that "having personally examined a large number of coralislands, and also residing

eight months among the volcanic class, having shore and partially encircling reefs, I may be permitted to state

that my own observations have impressed a conviction of the correctness of the theory of Mr. Darwin."

This gentleman believes, that subsequently to the subsidence by which the atolls in the Low Archipelago

were produced, the whole area has been elevated to the amount of a few feet; this would indeed be a

remarkable fact; but as far as I am able to judge, the grounds of his conclusion are not sufficiently strong. He

states that he found in almost every atoll which he visited, the shores of the lagoon raised from eighteen to

thirty inches above the sealevel, and containing imbedded Tridacnae and corals standing as they grew; some

of the corals were dead in their upper parts, but below a certain line they continued to flourish. In the lagoons,

also, he frequently met with clusters of Madrepore, with their extremities standing from one inch to a foot

above the surface of the water. Now, these appearances are exactly what I should have expected, without any

subsequent elevation having taken place; and I think Mr. Couthouy has not borne in mind the indisputable

fact, that corals, when constantly bathed by the surf, can exist at a higher level than in quite tranquil water, as

in a lagoon. As long, therefore, as the waves continued at low water to break entirely over parts of the annular

reef of an atoll, submerged to a small depth, the corals and shells attached on these parts might continue

living at a level above the smooth surface of the lagoon, into which the waves rolled; but as soon as the outer

edge of the reef grew up to its utmost possible height, or if the reef were very broad nearly to that height, the

force of the breakers would be checked, and the corals and shells on the inner parts near the lagoon would

occasionally be left dry, and thus be partially or wholly destroyed. Even in atolls, which have not lately

subsided, if the outer margin of the reef continued to increase in breadth seaward (each fresh zone of corals

rising to the same vertical height as at Keeling atoll), the line where the waves broke most heavily would

advance outwards, and therefore the corals, which when living near the margin, were washed by the breaking

waves during the whole of each tide, would cease being so, and would therefore be left on the backward part

of the reef standing exposed and dead. The case of the madrepores in the lagoons with the tops of their

branches exposed, seems to be an analogous fact, to the great fields of dead but upright corals in the lagoon

of Keeling atoll; a condition of things which I have endeavoured to show, has resulted from the lagoon

having become more and more enclosed and choked up with reefs, so that during high winds, the rising of the

tide (as observed by the inhabitants) is checked, and the corals, which had formerly grown to the greatest

possible height, are occasionally exposed, and thus are killed: and this is a condition of things, towards which

almost every atoll in the intervals of its subsidence must be tending. Or if we look to the state of an atoll

directly after a subsidence of some fathoms, the waves would roll heavily over the entire circumference of the

reef, and the surface of the lagoon would, like the ocean, never be quite at rest, and therefore the corals in the

lagoon, from being constantly laved by the rippling water, might extend their branches to a little greater

height than they could, when the lagoon became enclosed and protected. Christmas atoll (2 deg N. latitude)

which has a very shallow lagoon, and differs in several respects from most atolls, possibly may have been

elevated recently; but its highest part appears (Couthouy, page 46) to be only ten feet above the sealevel.

The facts of a second class, adduced by Mr. Couthouy, in support of the alleged recent elevation of the Low

Archipelago, are not all (especially those referring to a shelf of rock) quite intelligible to me; he believes that

certain enormous fragments of rock on the reef, must have been moved into their present position, when the

reef was at a lower level; but here again the force of the breakers on any inner point of the reef being

diminished by its outward growth without any change in its level, has not, I think, been borne in mind. We

should, also, not overlook the occasional agency of waves caused by earthquakes and hurricanes. Mr.

Couthouy further argues, that since these great fragments were deposited and fixed on the reef, they have

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 64

been elevated; he infers this from the greatest amount of erosion not being near their bases, where they are

unceasingly washed by the reflux of the tides, but at some height on their sides, near the line of highwater

mark, as shown in an accompanying diagram. My former remark again applies here, with this further

observation, that as the waves have to roll over a wide space of reef before they reach the fragments, their

force must be greatly increased with the increasing depth of water as the tide rises, and therefore I should

have expected that the chief line of present erosion would have coincided with the line of highwater mark;

and if the reef had grown outwards, that there would have been lines of erosion at greater heights. The

conclusion, to which I am finally led by the interesting observations of Mr. Couthouy is, that the atolls in the

Low Archipelago have, like the Society Islands, remained at a stationary level for a long period: and this

probably is the ordinary course of events, subsidence supervening after long intervals of rest.)

Turning now to the red colour; as on our map, the areas which have sunk slowly downwards to great depths

are many and large, we might naturally have been led to conjecture, that with such great changes of level in

progress, the coasts which have been fringed probably for ages (for we have no reason to believe that

coralreefs are of short duration), would not have remained all this time stationary, but would frequently

have undergone movements of elevation. This supposition, we shall immediately see, holds good to a

remarkable extent; and although a stationary condition of the land can hardly ever be open to proof, from the

evidence being only negative, we are, in some degree, enabled to ascertain the correctness of the parts

coloured red on the map, by the direct testimony of upraised organic remains of a modern date. Before going

into the details on this head (printed in small type), I may mention, that when reading a memoir on coral

formations by MM. Quoy and Gaimard ("Annales des Sciences Nat." tom. vi., page 279, etc.) I was

astonished to find, for I knew that they had crossed both the Pacific and Indian Oceans, that their descriptions

were applicable only to reefs of the fringing class; but my astonishment ended satisfactorily, when I

discovered that, by a strange chance, all the islands which these eminent naturalists had visited, though

several in number, namely, the Mauritius, Timor, New Guinea, the Mariana, and Sandwich Archipelagoes,

could be shown by their own statements to have been elevated within a recent geological era.

In the eastern half of the Pacific, the SANDWICH Islands are all fringed, and almost every naturalist who has

visited them, has remarked on the abundance of elevated corals and shells, apparently identical with living

species. The Rev. W. Ellis informs me, that he has noticed round several parts of Hawaii, beds of

coraldetritus, about twenty feet above the level of the sea, and where the coast is low they extend far inland.

Upraised coralrock forms a considerable part of the borders of Oahu; and at Elizabeth Island ("Zoology of

Captain Beechey's Voyage," page 176. See also MM. Quoy and Gaimard in "Annales de Scien. Nat." tom.

vi.) it composes three strata, each about ten feet thick. Nihau, which forms the northern, as Hawaii does the

southern end of the group (350 miles in length), likewise seems to consist of coral and volcanic rocks. Mr.

Couthouy ("Remarks on Coral Formations," page 51.) has lately described with interesting details, several

upraised beaches, ancient reefs with their surfaces perfectly preserved, and beds of recent shells and corals, at

the islands of Maui, Morokai, Oahu, and Tauai (or Kauai) in this group. Mr. Pierce, an intelligent resident at

Oahu, is convinced, from changes which have taken place within his memory, during the last sixteen years,

"that the elevation is at present going forward at a very perceptible rate." The natives at Kauai state that the

land is there gaining rapidly on the sea, and Mr. Couthouy has no doubt, from the nature of the strata, that

In the southern part of the Low Archipelago, Elizabeth Island is described by Captain Beechey (Beechey's

"Voyage in the Pacific," page 46, 4to edition.), as being quite flat, and about eighty feet in height; it is

entirely composed of dead corals, forming a honeycombed, but compact rock. In cases like this, of an island

having exactly the appearance, which the elevation of any one of the smaller surrounding atolls with a

shallow lagoon would present, one is led to conclude (with little better reason, however, than the

improbability of such small and low fabrics lasting, for an immense period, exposed to the many destroying

agents of nature), that the elevation has taken place at an epoch not geologically remote. When merely the

surface of an island of ordinary formation is strewed with marine bodies, and that continuously, or nearly so,

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 65

from the beach to a certain height, and not above that height, it is exceedingly improbable that such organic

remains, although they may not have been specially examined, should belong to any ancient period. It is

necessary to bear these remarks in mind, in considering the evidence of the elevatory movements in the

Pacific and Indian Oceans, as it does not often rest on specific determinations, and therefore should be

received with caution. Six of the COOK AND AUSTRAL Islands (S.W. of the Society group), are fringed; of

these, five were described to me by the Rev. J. Williams, as formed of coralrock, associated with some

basalt in Mangaia), and the sixth as lofty and basaltic. Mangaia is nearly three hundred feet high, with a level

summit; and according to Mr. S. Wilson (Couthouy's "Remarks," page 34.) it is an upraised reef; "and there

are in the central hollow, formerly the bed of the lagoon, many scattered patches of coralrock, some of them

raised to a height of forty feet." These knolls of coralrock were evidently once separate reefs in the lagoon

of an atoll. Mr. Martens, at Sydney, informed me that this island is surrounded by a terracelike plain at

about the height of a hundred feet, which probably marks a pause in its elevation. From these facts we may

infer, perhaps, that the Cook and Austral Islands have been upheaved at a period probably not very remote.

SAVAGE Island (S.E. of the Friendly group), is about forty feet in height. Forster ("Observations made

during Voyage round the World," page 147.) describes the plants as already growing out of the dead, but still

upright and spreading trees of coral; and the younger Forster ("Voyage," volume ii., page 163.) believes that

an ancient lagoon is now represented by a central plain; here we cannot doubt that the elevatory forces have

recently acted. The same conclusion may be extended, though with somewhat less certainty, to the islands of

the FRIENDLY GROUP, which have been well described in the second and third voyages of Cook. The

surface of Tongatabou is low and level, but with some parts a hundred feet high; the whole consists of

coralrock, "which yet shows the cavities and irregularities worn into it by the action of the tides." (Cook's

"Third Voyage" (4to edition), volume i., page 314.) On Eoua the same appearances were noticed at an

elevation of between two hundred and three hundred feet. Vavao, also, at the opposite or northern end of the

group, consists, according to the Rev. J. Williams, of coralrock. Tongatabou, with its northern extensive

reefs, resembles either an upraised atoll with one half originally imperfect, or one unequally elevated; and

Anamouka, an atoll equally elevated. This latter island contains (Ibid., volume i., page 235.) in its centre a

saltwater lake, about a mileandahalf in diameter, without any communication with the sea, and around it

the land rises gradually like a bank; the highest part is only between twenty and thirty feet; but on this part, as

well as on the rest of the land (which, as Cook observes, rises above the height of true lagoonislands),

coralrock, like that on the beach, was found. In the NAVIGATOR ARCHIPELAGO, Mr. Couthouy

("Remarks on CoralFormations," page 50.) found on Manua many and very large fragments of coral at the

height of eighty feet, "on a steep hillside, rising half a mile inland from a low sandy plain abounding in

marine remains." The fragments were embedded in a mixture of decomposed lava and sand. It is not stated

whether they were accompanied by shells, or whether the corals resembled recent species; as these remains

were embedded they possibly may belong to a remote epoch; but I presume this was not the opinion of Mr.

Still proceeding westward we come to the NEW HEBRIDES; on these islands, Mr. G. Bennett (author of

"Wanderings in New South Wales"), informs me he found much coral at a great altitude, which he considered

of recent origin. Respecting SANTA CRUZ, and the SOLOMON ARCHIPELAGO, I have no information;

but at New Ireland, which forms the northern point of the latter chain, both Labillardiere and Lesson have

described large beds of an apparently very modern madreporitic rock, with the form of the corals little

altered. The latter author ("Voyage de la 'Coquille'," Part. Zoolog.) states that this formation composes a

newer line of coast, modelled round an ancient one. There only remains to be described in the Pacific, that

curved line of fringed islands, of which the MARIANAS form the main part. Of these Guam, Rota, Tiniam,

Saypan, and some islets farther north, are described by Quoy and Gaimard (Freycinet's "Voyage autour du

Monde." See also the "Hydrographical Memoir," page 215.), and Chamisso (Kotzebue's "First Voyage."), as

chiefly composed of madreporitic limestone, which attains a considerable elevation, and is in several cases

worn into successively rising cliffs: the two former naturalists seem to have compared the corals and shells

with the existing ones, and state that they are of recent species. FAIS, which lies in the prolonged line of the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 66

Marianas, is the only island in this part of the sea which is fringed; it is ninety feet high, and consists entirely

In the EAST INDIAN ARCHIPELAGO, many authors have recorded proofs of recent elevation. M. Lesson

(Partie Zoolog., "Voyage de la 'Coquille'.") states, that near Port Dory, on the north coast of New Guinea, the

shores are flanked, to the height of 150 feet, by madreporitic strata of modern date. He mentions similar

formations at Waigiou, Amboina, Bourou, Ceram, Sonda, and Timor: at this latter place, MM. Quoy and

Gaimard ("Ann. des Scien. Nat." tom. vi., page 281.) have likewise described the primitive rocks, as coated to

a considerable height with coral. Some small islets eastward of Timor are said in Kolff's "Voyage,"

(translated by Windsor Earl, chapters vi., vii.) to resemble small coral islets upraised some feet above the sea.

Dr. Malcolmson informs me that Dr. Hardie found in JAVA an extensive formation, containing an abundance

of shells, of which the greater part appear to be of existing species. Dr. Jack ("Geolog. Transact." 2nd series,

volume i., page 403. On the Peninsula of Malacca, in front of Pinang, 5 deg 30' N., Dr. Ward collected some

shells, which Dr. Malcolmson informs me, although not compared with existing species, had a recent

appearance. Dr. Ward describes in this neighbourhood ("Trans. Asiat. Soc." volume xviii., part ii., page 166)

a single waterworn rock, with a conglomerate of seashells at its base, situated six miles inland, which,

according to the traditions of the natives, was once surrounded by the sea. Captain Low has also described

(Ibid., part i., page 131) mounds of shells lying two miles inland on this line of coast.) has described some

upraised shells and corals, apparently recent, on Pulo Nias off SUMATRA; and Marsden relates in his history

of this great island, that the names of many promontories, show that they were originally islands. On part of

the west coast of BORNEO and at the SOOLOO Islands, the form of the land, the nature of the soil, and the

waterwashed rocks, present appearances ("Notices of the East Indian Arch." Singapore, 1828, page 6, and

Append., page 43.) (although it is doubtful whether such vague evidence is worthy of mention), of having

recently been covered by the sea; and the inhabitants of the Sooloo Islands believe that this has been the case.

Mr. Cuming, who has lately investigated, with so much success, the natural history of the PHILIPPINES,

found near Cabagan, in Luzon, about fifty feet above the level of the R. Cagayan, and seventy miles from its

mouth, a large bed of fossil shells: these, he informs me, are of the same species with those now existing on

the shores of the neighbouring islands. From the accounts given us by Captain Basil Hall and Captain

Beechey (Captain B. Hall, "Voyage to Loo Choo," Append., pages xxi. and xxv. Captain Beechey's

"Voyage," page 496.) of the lines of inland reefs, and walls of coralrock worn into caves, above the present

reach of the waves, at the LOO CHOO Islands, there can be little doubt that they have been upraised at no

Dr. Davy describes the northern province of CEYLON ("Travels in Ceylon," page 13. This madreporitic

formation is mentioned by M. Cordier in his report to the Institute (May 4th, 1839), on the voyage of the

"Chevrette", as one of immense extent, and belonging to the latest tertiary period.) as being very low, and

consisting of a limestone with shells and corals of very recent origin; he adds, that it does not admit of a

doubt that the sea has retired from this district even within the memory of man. There is also some reason for

believing that the western shores of India, north of Ceylon, have been upraised within the recent period. (Dr.

Benza, in his "Journey through the N. Circars" (the "Madras Lit. and Scient. Journ." volume v.) has described

a formation with recent freshwater and marine shells, occurring at the distance of three or four miles from

the present shore. Dr. Benza, in conversation with me, attributed their position to a rise of the land. Dr.

Malcolmson, however (and there cannot be a higher authority on the geology of India) informs me that he

suspects that these beds may have been formed by the mere action of the waves and currents accumulating

sediment. From analogy I should much incline to Dr. Benza's opinion.) MAURITIUS has certainly been

upraised within the recent period, as I have stated in the chapter on fringingreefs. The northern extremity of

MADAGASCAR is described by Captain Owen (Owen's "Africa," volume ii., page 37, for Madagascar; and

for S. Africa, volume i., pages 412 and 426. Lieutenant Boteler's narrative contains fuller particulars

regarding the coralrock, volume i., page 174, and volume ii., pages 41 and 54. See also Ruschenberger's

"Voyage round the World," volume i., page 60.) as formed of madreporitic rock, as likewise are the shores

and outlying islands along an immense space of EASTERN AFRICA, from a little north of the equator for

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 67

nine hundred miles southward. Nothing can be more vague than the expression "madreporitic rock;" but at

the same time it is, I think, scarcely possible to look at the chart of the linear islets, which rise to a greater

height than can be accounted for by the growth of coral, in front of the coast, from the equator to 2 deg S.,

without feeling convinced that a line of fringingreefs has been elevated at a period so recent, that no great

changes have since taken place on the surface of this part of the globe. Some, also, of the higher islands of

madreporitic rock on this coast, for instance Pemba, have very singular forms, which seem to show the

combined effect of the growth of coral round submerged banks, and their subsequent upheaval. Dr. Allan

informs me that he never observed any elevated organic remains on the SEYCHELLES, which come under

The nature of the formations round the shores of the RED SEA, as described by several authors, shows that

the whole of this large area has been elevated within a very recent tertiary epoch. A part of this space in the

appended map, is coloured blue, indicating the presence of barrierreefs: on which circumstance I shall

presently make some remarks. Ruppell (Ruppell, "Reise in Abyssinien," Band i., s. 141.) states that the

tertiary formation, of which he has examined the organic remains, forms a fringe along the shores with a

uniform height of from thirty and forty feet from the mouth of the Gulf of Suez to about latitude 26 deg; but

that south of 26 deg, the beds attain only the height of from twelve to fifteen feet. This, however, can hardly

be quite accurate; although possibly there may be a decrease in the elevation of the shores in the middle parts

of the Red Sea, for Dr. Malcolmson (as he informs me) collected from the cliffs of Camaran Island (latitude

15 deg 30' S.) shells and corals, apparently recent, at a height between thirty and forty feet; and Mr. Salt

("Travels in Abyssinia") describes a similar formation a little southward on the opposite shore at Amphila.

Moreover, near the mouth of the Gulf of Suez, although on the coast opposite to that on which Dr. Ruppell

says that the modern beds attain a height of only thirty to forty feet, Mr. Burton (Lyell's "Principles of

Geology," 5th edition, volume iv., page 25.) found a deposit replete with existing species of shells, at the

height of 200 feet. In an admirable series of drawings by Captain Moresby, I could see how continuously the

cliffbounded low plains of this formation extended with a nearly equable height, both on the eastern and

western shores. The southern coast of Arabia seems to have been subjected to the same elevatory movement,

for Dr. Malcolmson found at Sahar low cliffs containing shells and corals, apparently of recent species.

The PERSIAN GULF abounds with coralreefs; but as it is difficult to distinguish them from sandbanks in

this shallow sea, I have coloured only some near the mouth; towards the head of the gulf Mr. Ainsworth

(Ainsworth's "Assyria and Babylon," page 217.) says that the land is worn into terraces, and that the beds

contain organic remains of existing forms. The WEST INDIAN ARCHIPELAGO of "fringed" islands, alone

remains to be mentioned; evidence of an elevation within a late tertiary epoch of nearly the whole of this

great area, may be found in the works of almost all the naturalists who have visited it. I will give some of the

principal references in a note. (On Florida and the north shores of the Gulf of Mexico, Rogers' "Report to

Brit. Assoc." volume iii., page 14.On the shores of Mexico, Humboldt, "Polit. Essay on New Spain,"

volume i., page 62. (I have also some corroborative facts with respect to the shores of Mexico.)Honduras

and the Antilles, Lyell's "Principles," 5th edition, volume iv., page 22.Santa Cruz and Barbadoes, Prof.

Hovey, "Silliman's Journal", volume xxxv., page 74.St. Domingo, Courrojolles, "Journ de Phys." tom. liv.,

page 106.Bahamas, "United Service Journal", No. lxxi., pages 218 and 224. Jamaica, De la Beche, "Geol.

Man." page 142.Cuba, Taylor in "Lond. and Edin. Mag." volume xi., page 17. Dr. Daubeny also, at a

meeting of the Geolog. Soc., orally described some very modern beds lying on the N.W. parts of Cuba. I

It is very remarkable on reviewing these details, to observe in how many instances fringingreefs round the

shores, have coincided with the existence on the land of upraised organic remains, which seem, from

evidence more or less satisfactory, to belong to a late tertiary period. It may, however, be objected, that

similar proofs of elevation, perhaps, occur on the coasts coloured blue in our map: but this certainly is not the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 68

The entire area of the Red Sea appears to have been upraised within a modern period; nevertheless I have

been compelled (though on unsatisfactory evidence, as given in the Appendix) to class the reefs in the middle

part, as barrierreefs; should, however, the statements prove accurate to the less height of the tertiary bed in

this middle part, compared with the northern and southern districts, we might well suspect that it had

subsided subsequently to the general elevation by which the whole area has been upraised. Several authors

(Ellis, in his "Polynesian Researches," was the first to call attention to these remains (volume i., page 38), and

the tradition of the natives concerning them. See also Williams, "Nar. of Missionary Enterprise," page 21;

also Tyerman and G. Bennett, "Journal of Voyage," volume i., page 213; also Mr. Couthouy's "Remarks,"

page 51; but this principal fact, namely, that there is a mass of upraised coral on the narrow peninsula of

Tiarubu, is from hearsay evidence; also Mr. Stutchbury, "West of England Journal," No. i., page 54. There is

a passage in Von Zach, "Corres. Astronom." volume x., page 266, inferring an uprising at Tahiti, from a

footpath now used, which was formerly impassable; but I particularly inquired from several native chiefs,

whether they knew of any change of this kind, and they were unanimous in giving me an answer in the

negative.) have stated that they have observed shells and corals high up on the mountains of the Society

Islands,a group encircled by barrierreefs, and, therefore, supposed to have subsided: at Tahiti Mr.

Stutchbury found on the apex of one of the highest mountains, between 5,000 and 7,000 feet above the level

of the sea, "a distinct and regular stratum of semifossil coral." At Tahiti, however, other naturalists, as well

as myself, have searched in vain at a low level near the coast, for upraised shells or masses of coralreef,

where if present they could hardly have been overlooked. From this fact, I concluded that probably the

organic remains strewed high up on the surface of the land, had originally been embedded in the volcanic

strata, and had subsequently been washed out by the rain. I have since heard from the Rev. W. Ellis, that the

remains which he met with, were (as he believes) interstratified with an argillaceous tuff; this likewise was

the case with the shells observed by the Rev. D. Tyerman at Huaheine. These remains have not been

specifically examined; they may, therefore, and especially the stratum observed by Mr. Stutchbury at an

immense height, be contemporaneous with the first formation of the Society Islands, and be of any degree of

antiquity; or they may have been deposited at some subsequent, but probably not very recent, period of

elevation; for if the period had been recent, the entire surface of the coast land of these islands, where the

reefs are so extensive, would have been coated with upraised coral, which certainly is not the case. Two of

the Harvey, or Cook Islands, namely, Aitutaki and Manouai, are encircled by reefs, which extend so far from

the land, that I have coloured them blue, although with much hesitation, as the space within the reef is

shallow, and the outline of the land is not abrupt. These two islands consist of coralrock; but I have no

evidence of their recent elevation, besides, the improbability of Mangaia, a fringed island in the same group

(but distant 170 miles), having retained its nearly perfect atolllike structure, during any immense lapse of

time after its upheaval. The Red Sea, therefore, is the only area in which we have clear proofs of the recent

elevation of a district, which, by our theory (although the barrierreefs are there not well characterised), has

lately subsided. But we have no reason to be surprised at oscillation, of level of this kind having occasionally

taken place. There can be scarcely any doubt that Savage, Aurora (Aurora Island is described by Mr.

Couthouy ("Remarks," page 58); it lies 120 miles northeast of Tahiti; it is not coloured in the appended

map, because it does not appear to be fringed by living reefs. Mr. Couthouy describes its summit as

"presenting a broad tableland which declines a few feet towards the centre, where we may suppose the

lagoon to have been placed." It is about two hundred feet in height, and consists of reefrock and

conglomerate, with existing species of coral embedded in it. The island has been elevated at two successive

periods; the cliffs being marked halfway up with a horizontal waterworn line of deep excavations. Aurora

Island seems closely to resemble in structure Elizabeth Island, at the southern end of the Low Archipelago.),

and Mangaia Islands, and several of the islands in the Friendly group, existed originally as atolls, and these

have undoubtedly since been upraised to some height above the level of the sea; so that by our theory, there

has here, also, been an oscillation of level, elevation having succeeded subsidence, instead of, as in the

middle part of the Red Sea and at the Harvey Islands, subsidence having probably succeeded recent elevation.

It is an interesting fact, that Fais, which, from its composition, form, height, and situation at the western end

of the Caroline Archipelago, one is strongly induced to believe existed before its upheaval as an atoll, lies

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 69

exactly in the prolongation of the curved line of the Mariana group, which we know to be a line of recent

elevation. I may add, that Elizabeth Island, in the southern part of the Low Archipelago, which seems to have

had the same kind of origin as Fais, lies near Pitcairn Island, the only one in this part of the ocean which is

Before making some concluding remarks on the relations of the spaces coloured blue and red, it will be

convenient to consider the position on our map of the volcanoes historically known to have been in action. It

is impossible not to be struck, first with the absence of volcanoes in the great areas of subsidence tinted pale

and dark blue,namely, in the central parts of the Indian Ocean, in the China Sea, in the sea between the

barriers of Australia and New Caledonia, in the Caroline, Marshall, Gilbert, and Low Archipelagoes; and,

secondly, with the coincidence of the principal volcanic chains with the parts coloured red, which indicates

the presence of fringingreefs; and, as we have just seen, the presence in most cases of upraised organic

remains of a modern date. I may here remark that the reefs were all coloured before the volcanoes were added

The volcano in Torres Strait, at the northern point of Australia, is that which lies nearest to a large subsiding

area, although situated 125 miles within the outer margin of the actual barrierreef. The Great Comoro

Island, which probably contains a volcano, is only twenty miles distant from the barrierreef of Mohila;

Ambil volcano, in the Philippines, is distant only a little more than sixty miles from the atollformed Appoo

reef: and there are two other volcanoes in the map within ninety miles of circles coloured blue. These few

cases, which thus offer partial exceptions to the rule, of volcanoes being placed remote from the areas of

subsidence, lie either near single and isolated atolls, or near small groups of encircled islands; and these by

our theory can have, in few instances, subsided to the same amount in depth or area, as groups of atolls.

There is not one active volcano within several hundred miles of an archipelago, or even a small group of

atolls. It is, therefore, a striking fact that in the Friendly Archipelago, which owes its origin to the elevation of

a group of atolls, two volcanoes, and, perhaps, others are known to be in action: on the other hand, on several

of the encircled islands in the Pacific, supposed by our theory to have subsided, there are old craters and

streams of lava, which show the effects of past and ancient eruptions. In these cases, it would appear as if the

volcanoes had come into action, and had become extinguished on the same spots, according as the elevating

There are some other coasts on the map, where volcanoes in a state of action concur with proofs of recent

elevation, besides those coloured red from being fringed by coralreefs. Thus I hope to show in a future

volume, that nearly the whole line of the west coast of South America, which forms the greatest volcanic

chain in the world, from near the equator for a space of between 2,000 and 3,000 miles southward, has

undergone an upward movement during a late geological period. The islands on the northwestern shores of

the Pacific, which form the second greatest volcanic chain, are very imperfectly known; but Luzon, in the

Philippines, and the Loo Choo Islands, have been recently elevated; and at Kamtschatka (At Sedanka, in

latitude 58 deg N. (Von Buch's "Descrip. des Isles Canaries," page 455). In a forthcoming part, I shall give

the evidence referred to with respect to the elevation of New Zealand.) there are extensive tertiary beds of

modern date. Evidence of the same nature, but not very satisfactory, may be detected in Northern New

Zealand where there are two volcanoes. The coexistence in other parts of the world of active volcanoes,

with upraised beds of a modern tertiary origin, will occur to every geologist. (During the subterranean

disturbances which took place in Chile, in 1835, I have shown ("Geolog. Trans." 2nd Ser., vol. v., page 606)

that at the same moment that a large district was upraised, volcanic matter burst forth at widely separated

points, through both new and old vents.) Nevertheless, until it could be shown that volcanoes were inactive,

or did not exist in subsiding areas, the conclusion that their distribution depended on the nature of the

subterranean movements in progress, would have been hazardous. But now, viewing the appended map, it

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 70

may, I think, be considered as almost established, that volcanoes are often (not necessarily always) present in

those areas where the subterranean motive power has lately forced, or is now forcing outwards, the crust of

the earth, but that they are invariably absent in those, where the surface has lately subsided or is still

subsiding. (We may infer from this rule, that in any old deposit, which contains interstratified beds of erupted

matter, there was at the period, and in the area of its formation, a TENDENCY to an upward movement in the

The immense surfaces on the map, which, both by our theory and by the plain evidence of upraised marine

remains, have undergone a change of level either downwards or upwards during a late period, is a most

remarkable fact. The existence of continents shows that the areas have been immense which at some period

have been upraised; in South America we may feel sure, and on the northwestern shores of the Indian Ocean

we may suspect, that this rising is either now actually in progress, or has taken place quite recently. By our

theory, we may conclude that the areas are likewise immense which have lately subsided, or, judging from

the earthquakes occasionally felt and from other appearances, are now subsiding. The smallness of the scale

of our map should not be overlooked: each of the squares on it contains (not allowing for the curvature of the

earth) 810,000 square miles. Look at the space of ocean from near the southern end of the Low Archipelago

to the northern end of the Marshall Archipelago, a length of 4,500 miles, in which, as far as is known, every

island, except Aurora which lies just without the Low Archipelago, is atollformed. The eastern and western

boundaries of our map are continents, and they are rising areas: the central spaces of the great Indian and

Pacific Oceans, are mostly subsiding; between them, north of Australia, lies the most broken land on the

globe, and there the rising parts are surrounded and penetrated by areas of subsidence (I suspect that the Arru

and Timorlaut Islands present an included small area of subsidence, like that of the China Sea, but I have

not ventured to colour them from my imperfect information, as given in the Appendix.), so that the prevailing

movements now in progress, seem to accord with the actual states of surface of the great divisions of the

The blue spaces on the map are nearly all elongated; but it does not necessarily follow from this (a caution,

for which I am indebted to Mr. Lyell), that the areas of subsidence were likewise elongated; for the

subsidence of a long, narrow space of the bed of the ocean, including in it a transverse chain of mountains,

surmounted by atolls, would only be marked on the map by a transverse blue band. But where a chain of

atolls and barrierreefs lies in an elongated area, between spaces coloured red, which therefore have

remained stationary or have been upraised, this must have resulted either from the area of subsidence having

originally been elongated (owing to some tendency in the earth's crust thus to subside), or from the subsiding

area having originally been of an irregular figure, or as broad as long, and having since been narrowed by the

elevation of neighbouring districts. Thus the areas, which subsided during the formation of the great north

and south lines of atolls in the Indian Ocean,of the east and west line of the Caroline atolls,and of the

northwest and southeast line of the barrierreefs of New Caledonia and Louisiade, must have originally

been elongated, or if not so, they must have since been made elongated by elevations, which we know to

I infer from Mr. Hopkins' researches ("Researches in Physical Geology," Transact. Cambridge Phil. Soc.,

volume vi, part i.), that for the formation of a long chain of mountains, with few lateral spurs, an area

elongated in the same direction with the chain, must have been subjected to an elevatory movement.

Mountainchains, however, when already formed, although running in very different directions, it seems (For

instance in S. America from latitude 34 deg, for very many degrees southward there are upraised beds

containing recent species of shells, on both the Atlantic and Pacific side of the continent, and from the

gradual ascent of the land, although with very unequal slopes, on both sides towards the Cordillera, I think it

can hardly be doubted that the entire width has been upraised in mass within the recent period. In this case the

two W.N.W. and E.S.E. mountainlines, namely the Sierra Ventana and the S. Tapalguen, and the great north

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 71

and south line of the Cordillera have been together raised. In the West Indies the N. and S. line of the Eastern

Antilles, and the E. and W. line of Jamaica, appear both to have been upraised within the latest geological

period.) may be raised together by a widelyacting force: so, perhaps, mountainchains may subside

together. Hence, we cannot tell, whether the Caroline and Marshall Archipelagoes, two groups of atolls

running in different directions and meeting each other, have been formed by the subsidence of two areas, or

of one large area, including two distinct lines of mountains. We have, however, in the southern prolongation

of the Mariana Islands, probable evidence of a line of recent elevation having intersected one of recent

subsidence. A view of the map will show that, generally, there is a tendency to alternation in the parallel

areas undergoing opposite kinds of movement; as if the sinking of one area balanced the rising of another.

The existence in many parts of the world of high tableland, proves that large surfaces have been upraised in

mass to considerable heights above the level of the ocean; although the highest points in almost every country

consist of upturned strata, or erupted matter: and from the immense spaces scattered with atolls, which

indicate that land originally existed there, although not one pinnacle now remains above the level of the sea,

we may conclude that wide areas have subsided to an amount, sufficient to bury not only any formerly

existing tableland, but even the heights formed by fractured strata, and erupted matter. The effects produced

on the land by the later elevatory movements, namely, successively rising cliffs, lines of erosion, and beds of

literal shells and pebbles, all requiring time for their production, prove that these movements have been very

slow; we can, however, infer this with safety, only with respect to the few last hundred feet of rise. But with

reference to the whole vast amount of subsidence, necessary to have produced the many atolls widely

scattered over immense spaces, it has already been shown (and it is, perhaps, the most interesting conclusion

in this volume), that the movements must either have been uniform and exceedingly slow, or have been

effected by small steps, separated from each other by long intervals of time, during which the

reefconstructing polypifers were able to bring up their solid frameworks to the surface. We have little means

of judging whether many considerable oscillations of level have generally occurred during the elevation of

large tracts; but we know, from clear geological evidence, that this has frequently taken place; and we have

seen on our map, that some of the same islands have both subsided and been upraised. I conclude, however,

that most of the large blue spaces, have subsided without many and great elevatory oscillations, because only

a few upraised atolls have been observed: the supposition that such elevations have taken place, but that the

upraised parts have been worn down by the surf, and thus have escaped observation, is overruled by the very

considerable depth of the lagoons of all the larger atolls; for this could not have been the case, if they had

suffered repeated elevations and abrasion. From the comparative observations made in these latter pages, we

may finally conclude, that the subterranean changes which have caused some large areas to rise, and others to

In the three first chapters, the principal kinds of coralreefs were described in detail, and they were found to

differ little, as far as relates to the actual surface of the reef. An atoll differs from an encircling barrierreef

only in the absence of land within its central expanse; and a barrierreef differs from a fringingreef, in being

placed at a much greater distance from the land with reference to the probable inclination of its submarine

foundation, and in the presence of a deepwater lagoonlike space or moat within the reef. In the fourth

chapter the growing powers of the reefconstructing polypifers were discussed; and it was shown, that they

cannot flourish beneath a very limited depth. In accordance with this limit, there is no difficulty respecting

the foundations on which fringingreefs are based; whereas, with barrierreefs and atolls, there is a great

apparent difficulty on this head; in barrierreefs from the improbability of the rock of the coast or of banks of

sediment extending, in every instance, so far seaward within the required depth;and in atolls, from the

immensity of the spaces over which they are interspersed, and the apparent necessity for believing that they

are all supported on mountainsummits, which although rising very near to the surfacelevel of the sea, in no

one instance emerge above it. To escape this latter most improbable admission, which implies the existence

of submarine chains of mountains of almost the same height, extending over areas of many thousand square

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 72

miles, there is but one alternative; namely, the prolonged subsidence of the foundations, on which the atolls

were primarily based, together with the upward growth of the reefconstructing corals. On this view every

difficulty vanishes; fringing reefs are thus converted into barrierreefs; and barrierreefs, when encircling

islands, are thus converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the

Thus the ordinary forms and certain peculiarities in the structure of atolls and barrierreefs can be

explained;namely, the walllike structure on their inner sides, the basin or ringlike shape both of the

marginal and central reefs in the Maldiva atollsthe union of some atolls as if by a ribbonthe apparent

disseverment of othersand the occurrence, in atolls as well as in barrierreefs, of portions of reef, and of

the whole of some reefs, in a dead and submerged state, but retaining the outline of living reefs. Thus can be

explained the existence of breaches through barrierreefs in front of valleys, though separated from them by

a wide space of deep water; thus, also, the ordinary outline of groups of atolls and the relative forms of the

separate atolls one to another; thus can be explained the proximity of the two kinds of reefs formed during

subsidence, and their separation from the spaces where fringingreefs abound. On searching for other

evidence of the movements supposed by our theory, we find marks of change in atolls and in barrierreefs,

and of subterranean disturbances under them; but from the nature of things, it is scarcely possible to detect

any direct proofs of subsidence, although some appearances are strongly in favour of it. On the fringed

coasts, however, the presence of upraised marine bodies of a recent epoch, plainly show, that these coasts,

instead of having remained stationary, which is all that can be directly inferred from our theory, have

Finally, when the two great types of structure, namely barrierreefs and atolls on the one hand, and

fringingreefs on the other, were laid down in colours on our map, a magnificent and harmonious picture of

the movements, which the crust of the earth has within a late period undergone, is presented to us. We there

see vast areas rising, with volcanic matter every now and then bursting forth through the vents or fissures

with which they are traversed. We see other wide spaces slowly sinking without any volcanic outburst, and

we may feel sure, that this sinking must have been immense in amount as well as in area, thus to have buried

over the broad face of the ocean every one of those mountains, above which atolls now stand like

monuments, marking the place of their former existence. Reflecting how powerful an agent with respect to

denudation, and consequently to the nature and thickness of the deposits in accumulation, the sea must ever

be, when acting for prolonged periods on the land, during either its slow emergence or subsidence; reflecting,

also, on the final effects of these movements in the interchange of land and oceanwater on the climate of the

earth, and on the distribution of organic beings, I may be permitted to hope, that the conclusions derived from

the study of coralformations, originally attempted merely to explain their peculiar forms, may be thought

In the beginning of the last chapter I stated the principles on which the map is coloured. There only remains

to be said, that it is an exact copy of one by M. C. Gressier, published by the Depot General de la Marine, in

1835. The names have been altered into English, and the longitude has been reduced to that of Greenwich.

The colours were first laid down on accurate charts, on a large scale. The data, on which the volcanoes

historically known to have been in action, have been marked with vermillion, were given in a note to the last

chapter. I will commence my description on the eastern side of the map, and will describe each group of

islands consecutively, proceeding westward across the Pacific and Indian Oceans, but ending with the West

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 73

The WESTERN SHORES OF AMERICA appear to be entirely without coralreefs; south of the equator the

survey of the "Beagle", and north of it, the published charts show that this is the case. Even in the Bay of

PANAMA, where corals flourish, there are no true coralreefs, as I have been informed by Mr. Lloyd. There

are no coralreefs in the GALAPAGOS Archipelago, as I know from personal inspection; and I believe there

are none on the COCOS, REVILLAGIGEDO, and other neighbouring islands. CLIPPERTON rock, 10 deg

N., 109 deg W., has lately been surveyed by Captain Belcher; in form it is like the crater of a volcano. From a

drawing appended to the MS. plan in the Admiralty, it evidently is not an atoll. The eastern parts of the

Pacific present an enormous area, without any islands, except EASTER, and SALA, and GOMEZ Islands,

This group consists of about eighty atolls: it will be quite superfluous to refer to descriptions of each. In

D'Urville and Lottin's chart, one island (WOLCHONSKY) is written with a capital letter, signifying, as

explained in a former chapter, that it is a high island; but this must be a mistake, as the original chart by

Bellinghausen shows that it is a true atoll. Captain Beechey says of the thirtytwo groups which he examined

(of the greater number of which I have seen beautiful MS. charts in the Admiralty), that twentynine now

contain lagoons, and he believes the other three originally did. Bellinghausen (see an account of his Russian

voyage, in the "Biblioth. des Voyages," 1834, page 443) says, that the seventeen islands which he discovered

resembled each other in structure, and he has given charts on a large scale of all of them. Kotzebue has given

plans of several; Cook and Bligh mention others; a few were seen during the voyage of the "Beagle"; and

notices of other atolls are scattered through several publications. The ACTAEON group in this archipelago

has lately been discovered ("Geographical Journal", volume vii., page 454); it consists of three small and low

islets, one of which has a lagoon. Another lagoonisland has been discovered ("Naut. Mag." 1839, page 770),

in 22 deg 4' S., and 136 deg 20' W. Towards the S.E. part of the group, there are some islands of different

formation: ELIZABETH Island is described by Beechey (page 46, 4to edition) as fringed by reefs, at the

distance of between two and three hundred yards; coloured red. PITCAIRN Island, in the immediate

neighbourhood, according to the same authority, has no reefs of any kind, although numerous pieces of coral

are thrown up on the beach; the sea close to its shore is very deep (see "Zool. of Beechey's Voyage," page

164); it is left uncoloured. GAMBIER Islands (see Plate I., Figure 8), are encircled by a barrierreef; the

greatest depth within is thirtyeight fathoms; coloured pale blue. AURORA Island, which lies N.E. of Tahiti

close to the large space coloured dark blue in the map, has been already described in a note (page 71), on the

authority of Mr. Couthouy; it is an upraised atoll, but as it does not appear to be fringed by living reefs, it is

The SOCIETY Archipelago is separated by a narrow space from the Low Archipelago; and in their parallel

direction they manifest some relation to each other. I have already described the general character of the reefs

of these fine encircled islands. In the "Atlas of the 'Coquille's' Voyage" there is a good general chart of the

group, and separate plans of some of the islands. TAHITI, the largest island in the group, is almost

surrounded, as seen in Cook's chart, by a reef from half a mile to a mile and a half from the shore, with from

ten to thirty fathoms within it. Some considerable submerged reefs lying parallel to the shore, with a broad

and deep space within, have lately been discovered ("Naut. Mag." 1836, page 264) on the N.E. coast of the

island, where none are laid down by Cook. At EIMEO the reef "which like a ring surrounds it, is in some

places one or two miles distant from the shore, in others united to the beach" (Ellis, "Polynesian Researches,"

volume i., page 18, 12mo edition). Cook found deep water (twenty fathoms) in some of the harbours within

the reef. Mr. Couthouy, however, states ("Remarks," page 45) that both at Tahiti and Eimeo, the space

between the barrierreef and the shore, has been almost filled up,"a nearly continuous fringingreef

surrounding the island, and varying from a few yards to rather more than a mile in width, the lagoons merely

forming canals between this and the seareef," that is the barrierreef. TAPAMANOA is surrounded by a

reef at a considerable distance from the shore; from the island being small it is breached, as I am informed by

the Rev. W. Ellis, only by a narrow and crooked boat channel. This is the lowest island in the group, its

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 74

height probably not exceeding 500 feet. A little way north of Tahiti, the low coralislets of TETUROA are

situated; from the description of them given me by the Rev. J. Williams (the author of the "Narrative of

Missionary Enterprise"), I should have thought they had formed a small atoll, and likewise from the

description given by the Rev. D. Tyerman and G. Bennett ("Journal of Voyage and Travels," volume i., page

183), who say that ten low coralislets "are comprehended within one general reef, and separated from each

other by interjacent lagoons;" but as Mr. Stutchbury ("West of England Journal," volume i., page 54)

describes it as consisting of a mere narrow ridge, I have left it uncoloured. MAITEA, eastward of the group,

is classed by Forster as a high encircled island; but from the account given by the Rev. D. Tyerman and G.

Bennett (volume i., page 57) it appears to be an exceedingly abrupt cone, rising from the sea without any

reef; I have left it uncoloured. It would be superfluous to describe the northern islands in this group, as they

may be well seen in the chart accompanying the 4to edition of Cook's "Voyages," and in the "Atlas of the

'Coquille's' Voyage." MAURUA is the only one of the northern islands, in which the water within the reef is

not deep, being only four and a half fathoms; but the great width of the reef, stretching three miles and a half

southward of the land (which is represented in the drawing in the "Atlas of the 'Coquille's' Voyage" as

descending abruptly to the water) shows, on the principle explained in the beginning of the last chapter, that it

belongs to the barrier class. I may here mention, from information communicated to me by the Rev. W. Ellis,

that on the N.E. side of HUAHEINE there is a bank of sand, about a quarter of a mile wide, extending

parallel to the shore, and separated from it by an extensive and deep lagoon; this bank of sand rests on

coralrock, and undoubtedly was originally a living reef. North of Bolabola lies the atoll of TOUBAI

(Motouiti of the "'Coquille's' Atlas") which is coloured dark blue; the other islands, surrounded by

barrierreefs, are pale blue; three of them are represented in Figures 3, 4, and 5, in Plate I. There are three

low coralgroups lying a little E. of the Society Archipelago, and almost forming part of it, namely

BELLINGHAUSEN, which is said by Kotzebue ("Second Voyage," volume ii., page 255), to be a

lagoonisland; MOPEHA, which, from Cook's description ("Second Voyage," book iii., chapter i.), no doubt

is an atoll; and the SCILLY Islands, which are said by Wallis ("Voyage," chapter ix.) to form a GROUP of

LOW islets and shoals, and, therefore, probably, they compose an atoll: the two former have been coloured

These islands are entirely without reefs, as may be seen in Krusenstern's Atlas, making a remarkable contrast

with the adjacent group of the Society Islands. Mr. F.D. Bennett has given some account of this group, in the

seventh volume of the "Geographical Journal". He informs me that all the islands have the same general

character, and that the water is very deep close to their shores. He visited three of them, namely,

DOMINICANA, CHRISTIANA, and ROAPOA; their beaches are strewed with rounded masses of coral, and

although no regular reefs exist, yet the shore is in many places lined by coralrock, so that a boat grounds on

this formation. Hence these islands ought probably to come within the class of fringed islands and be

coloured red; but as I am determined to err on the cautious side, I have left them uncoloured.

PALMERSTON Island is minutely described as an atoll by Captain Cook during his voyage in 1774;

coloured blue. AITUTAKI was partially surveyed by the "Beagle" (see map accompanying "Voyages of

'Adventure' and 'Beagle'"); the land is hilly, sloping gently to the beach; the highest point is 360 feet; on the

southern side the reef projects five miles from the land: off this point the "Beagle" found no bottom with 270

fathoms: the reef is surmounted by many low coralislets. Although within the reef the water is exceedingly

shallow, not being more than a few feet deep, as I am informed by the Rev. J. Williams, nevertheless, from

the great extension of this reef into a profoundly deep ocean, this island probably belongs, on the principle

lately adverted to, to the barrier class, and I have coloured it pale blue; although with much

hesitation.MANOUAI or HARVEY Island. The highest point is about fifty feet: the Rev. J. Williams

informs me that the reef here, although it lies far from the shore, is less distant than at Aitutaki, but the water

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 75

within the reef is rather deeper: I have also coloured this pale blue with many doubts.Round MITIARO

Island, as I am informed by Mr. Williams, the reef is attached to the shore; coloured red. MAUKI or

Maouti; the reef round this island (under the name of Parry Island, in the "Voyage of H.M.S. 'Blonde'," page

209) is described as a coralflat, only fifty yards wide, and two feet under water. This statement has been

corroborated by Mr. Williams, who calls the reef attached; coloured red.AITU, or Wateeo; a moderately

elevated hilly island, like the others of this group. The reef is described in Cook's "Voyage," as attached to

the shore, and about one hundred yards wide; coloured red.FENOUAITI; Cook describes this island as

very low, not more than six or seven feet high (volume i., book ii., chapter iii, 1777); in the chart published in

the "'Coquille's' Atlas," a reef is engraved close to the shore: this island is not mentioned in the list given by

Mr. Williams (page 16) in the "Narrative of Missionary Enterprise;" nature doubtful. As it is so near Atiu, it

has been unavoidably coloured red. RAROTONGA; Mr. Williams informs me that it is a lofty basaltic

island with an attached reef; coloured red.There are three islands, ROUROUTI, ROXBURGH, and HULL,

of which I have not been able to obtain any account, and have left them uncoloured. Hull Island, in the

French chart, is written with small letters as being low.MANGAIA; height about three hundred feet; "the

surrounding reef joins the shore" (Williams, "Narrative," page 18); coloured red.RIMETARA; Mr.

Williams informs me that the reef is rather close to the shore; but, from information given me by Mr. Ellis,

the reef does not appear to be quite so closely attached to it as in the foregoing cases: the island is about three

hundred feet high ("Naut. Mag." 1839, page 738); coloured red.RURUTU; Mr. Williams and Mr. Ellis

inform me that this island has an attached reef; coloured red. It is described by Cook under the name of

Oheteroa: he says it is not surrounded, like the neighbouring islands by a reef; he must have meant a distant

reef.TOUBOUAI; in Cook's chart ("Second Voyage," volume ii., page 2) the reef is laid down in part one

mile, and in part two miles from the shore. Mr. Ellis ("Polynes. Res." volume iii., page 381) says the low land

round the base of the island is very extensive; and this gentleman informs me that the water within the reef

appears deep; coloured blue.RAIVAIVAI, or Vivitao; Mr. Williams informs me that the reef is here

distant: Mr. Ellis, however, says that this is certainly not the case on one side of the island; and he believes

that the water within the reef is not deep; hence I have left it uncoloured.LANCASTER Reef, described in

"Naut. Mag." 1833 (page 693), as an extensive crescentformed coralreef. I have not coloured it.RAPA,

or Oparree; from the accounts given of it by Ellis and Vancouver, there does not appear to be any reef.I.

DE BASS is an adjoining island, of which I cannot find any account.KEMIN Island; Krusenstern seems

CAROLINE Island (10 deg S., 150 deg W.) is described by Mr. F.D. Bennett ("Geographical Journal",

volume vii., page 225) as containing a fine lagoon; coloured blue.FLINT Island (11 deg S., 151 deg W.);

Krusenstern believes that it is the same with Peregrino, which is described by Quiros (Burney's "Chron. Hist."

volume ii., page 283) as "a cluster of small islands connected by a reef, and forming a lagoon in the middle;"

coloured blue.WOSTOCK is an island a little more than half a mile in diameter, and apparently quite flat

and low, and was discovered by Bellinghausen; it is situated a little west of Caroline Island, but it is not

placed on the French charts; I have not coloured it, although I entertain little doubt from the chart of

Bellinghausen, that it originally contained a small lagoon.PENRHYN Island (9 deg S., 158 deg W.); a plan

of it in the "Atlas of the First Voyage" of Kotzebue, shows that it is an atoll; blue. SLARBUCK Island (5

deg S., 156 deg W.) is described in Byron's "Voyage in the 'Blonde'" (page 206) as formed of a flat

coralrock, with no trees; the height not given; not coloured.MALDEN Island (4 deg S., 154 deg W.); in

the same voyage (page 205) this island is said to be of coral formation, and no part above forty feet high; I

have not ventured to colour it, although, from being of coralformation, it is probably fringed; in which case

it should be red.JARVIS, or BUNKER Island (0 deg 20' S., 160 deg W.) is described by Mr. F.D. Bennett

("Geographical Journal", volume vii., page 227) as a narrow, low strip of coralformation; not

coloured.BROOK, is a small low island between the two latter; the position, and perhaps even the

existence of it is doubtful; not coloured.PESCADO and HUMPHREY Islands; I can find out nothing about

these islands, except that the latter appears to be small and low; not coloured.REARSON, or Grand Duke

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 76

Alexander's (10 S., 161 deg W.); an atoll, of which a plan is given by Bellinghausen; blue. SOUVOROFF

Islands (13 deg S., 163 deg W.); Admiral Krusenstern, in the most obliging manner, obtained for me an

account of these islands from Admiral Lazareff, who discovered them. They consist of five very low islands

of coralformation, two of which are connected by a reef, with deep water close to it. They do not surround a

lagoon, but are so placed that a line drawn through them includes an oval space, part of which is shallow;

these islets, therefore, probably once (as is the case with some of the islands in the Caroline Archipelago)

formed a single atoll; but I have not coloured them.DANGER Island (10 deg S., 166 deg W.); described as

low by Commodore Byron, and more lately surveyed by Bellinghausen; it is a small atoll with three islets on

it; blue.CLARENCE Island (9 deg S., 172 deg W.); discovered in the "Pandora" (G. Hamilton's "Voyage,"

page 75): it is said, "in running along the land, we saw several canoes crossing the LAGOONS;" as this island

is in the close vicinity of other low islands, and as it is said, that the natives make reservoirs of water in old

cocoanut trees (which shows the nature of the land), I have no doubt it is an atoll, and have coloured it blue.

YORK Island (8 deg S., 172 deg W.) is described by Commodore Byron (chapter x. of his "Voyage") as an

atoll; blue.SYDNEY Island (4 deg S., 172 deg W.) is about three miles in diameter, with its interior

occupied by a lagoon (Captain Tromelin, "Annal. Marit." 1829, page 297); blue.PHOENIX Island (4 deg

S., 171 deg W.) is nearly circular, low, sandy, not more than two miles in diameter, and very steep outside

(Tromelin, "Annal. Marit." 1829, page 297); it may be inferred that this island originally contained a lagoon,

but I have not coloured it.NEW NANTUCKET (0 deg 15' N., 174 deg W.). From the French chart it must

be a low island; I can find nothing more about it or about MARY Island; both uncoloured.GARDNER

Island (5 deg S., 174 deg W.) from its position is certainly the same as KEMIN Island described

(Krusenstern, page 435, Appen. to Mem., published 1827) as having a lagoon in its centre; blue.

CHRISTMAS Island (2 deg N., 157 deg W.). Captain Cook, in his "Third Voyage" (Volume ii., chapter x.),

has given a detailed account of this atoll. The breadth of the islets on the reef is unusually great, and the sea

near it does not deepen so suddenly as is generally the case. It has more lately been visited by Mr. F.D.

Bennett ("Geographical Journal," volume vii., page 226); and he assures me that it is low and of

coralformation: I particularly mention this, because it is engraved with a capital letter, signifying a high

island, in D'Urville and Lottin's chart. Mr. Couthouy, also, has given some account of it ("Remarks," page 46)

from the Hawaiian "Spectator"; he believes it has lately undergone a small elevation, but his evidence does

not appear to me satisfactory; the deepest part of the lagoon is said to be only ten feet; nevertheless, I have

coloured it blue.FANNING Island (4 deg N., 158 deg W.) according to Captain Tromelin ("Ann. Maritim."

1829, page 283), is an atoll: his account as observed by Krusenstern, differs from that given in Fanning's

"Voyage" (page 224), which, however, is far from clear; coloured blue. WASHINGTON Island (4 deg N.,

159 deg W.) is engraved as a low island in D'Urville's chart, but is described by Fanning (page 226) as having

a much greater elevation than Fanning Island, and hence I presume it is not an atoll; not

coloured.PALMYRA Island (6 deg N., 162 deg W.) is an atoll divided into two parts (Krusenstern's

"Mem. Suppl." page 50, also Fanning's "Voyage," page 233); blue.SMYTH'S or Johnston's Islands (17 deg

N., 170 deg W.). Captain Smyth, R.N., has had the kindness to inform me that they consist of two very low,

small islands, with a dangerous reef off the east end of them. Captain Smyth does not recollect whether these

HAWAII; in the chart in Freycinet's "Atlas," small portions of the coast are fringed by reefs; and in the

accompanying "Hydrog. Memoir," reefs are mentioned in several places, and the coral is said to injure the

cables. On one side of the islet of Kohaihai there is a bank of sand and coral with five feet water on it,

running parallel to the shore, and leaving a channel of about fifteen feet deep within. I have coloured this

island red, but it is very much less perfectly fringed than others of the group.MAUI; in Freycinet's chart of

the anchorage of Raheina, two or three miles of coast are seen to be fringed; and in the "Hydrog. Memoir,"

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 77

"banks of coral along shore" are spoken of. Mr. F.D. Bennett informs me that the reefs, on an average, extend

about a quarter of a mile from the beach; the land is not very steep, and outside the reefs the sea does not

become deep very suddenly; coloured red.MOROTOI, I presume, is fringed: Freycinet speaks of the

breakers extending along the shore at a little distance from it. From the chart, I believe it is fringed; coloured

red.OAHU; Freycinet, in his "Hydrog. Memoir," mentions some of the reefs. Mr. F.D. Bennett informs me

that the shore is skirted for forty or fifty miles in length. There is even a harbour for ships formed by the

reefs, but it is at the mouth of a valley; red.ATOOI, in La Peyrouse's charts, is represented as fringed by a

reef, in the same manner as Oahu and Morotoi; and this, as I have been informed by Mr. Ellis, on part at least

of the shore, is of coralformation: the reef does not leave a deep channel within; red.ONEEHOW; Mr.

Ellis believes that this island is also fringed by a coralreef: considering its close proximity to the other

islands, I have ventured to colour it red. I have in vain consulted the works of Cook, Vancouver, La Peyrouse,

and Lisiansky, for any satisfactory account of the small islands and reefs, which lie scattered in a N.W. line

prolonged from the Sandwich group, and hence have left them uncoloured, with one exception; for I am

indebted to Mr. F.D. Bennett for informing me of an atollformed reef, in latitude 28 deg 22', longitude 178

deg 30' W., on which the "Gledstanes" was wrecked in 1837. It is apparently of large size, and extends in a

N.W. and S.E. line: very few islets have been formed on it. The lagoon seems to be shallow; at least, the

deepest part which was surveyed was only three fathoms. Mr. Couthouy ("Remarks," page 38) describes this

island under the name of OCEAN island. Considerable doubts should be entertained regarding the nature of a

reef of this kind, with a very shallow lagoon, and standing far from any other atoll, on account of the

possibility of a crater or flat bank of rock lying at the proper depth beneath the surface of the water, thus

affording a foundation for a ringformed coralreef. I have, however, thought myself compelled, from its

Kotzebue, in his "Second Voyage," contrasts the structure of these islands with many others in the Pacific, in

not being furnished with harbours for ships, formed by distant coralreefs. The Rev. J. Williams, however,

informs me, that coralreefs do occur in irregular patches on the shores of these islands; but that they do not

form a continuous band, as round Mangaia, and other such perfect cases of fringed islands. From the charts

accompanying La Peyrouse's "Voyage," it appears that the north shore of SAVAII, MAOUNA,

OROSENGA, and MANUA, are fringed by reefs. La Peyrouse, speaking of Maouna (page 126), says that the

coralreef surrounding its shores, almost touches the beach; and is breached in front of the little coves and

streams, forming passages for canoes, and probably even for boats. Further on (page 159), he extends the

same observation to all the islands which he visited. Mr. Williams in his "Narrative," speaks of a reef going

round a small island attached to OYOLAVA, and returning again to it: all these islands have been coloured

red.A chart of ROSE Island, at the extreme west end of the group, is given by Freycinet, from which I

should have thought that it had been an atoll; but according to Mr. Couthouy ("Remarks," page 43), it

consists of a reef, only a league in circuit, surmounted by a very few low islets; the lagoon is very shallow,

and is strewed with numerous large boulders of volcanic rock. This island, therefore, probably consists of a

bank of rock, a few feet submerged, with the outer margin of its upper surface fringed with reefs; hence it

cannot be properly classed with atolls, in which the foundations are always supposed to lie at a depth, greater

BEVERIDGE Reef, 20 deg S., 167 deg W., is described in the "Naut. Mag." (May 1833, page 442) as ten

miles long in a N. and S. line, and eight wide; "in the inside of the reef there appears deep water;" there is a

passage near the S.W. corner: this therefore seems to be a submerged atoll, and is coloured blue.

SAVAGE Island, 19 deg S., 170 deg W., has been described by Cook and Forster. The younger Forster

(volume ii., page 163) says it is about forty feet high: he suspects that it contains a low plain, which formerly

was the lagoon. The Rev. J. Williams informs me that the reef fringing its shores, resembles that round

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 78

PYLSTAART Island. Judging from the chart in Freycinet's "Atlas," I should have supposed that it had been

regularly fringed; but as nothing is said in the "Hydrog. Memoir" (or in the "Voyage" of Tasman, the

discoverer) about coralreefs, I have left it uncoloured.TONGATABOU: In the "Atlas of the Voyage of

the 'Astrolabe'," the whole south side of the island is represented as narrowly fringed by the same reef which

forms an extensive platform on the northern side. The origin of this latter reef, which might have been

mistaken for a barrierreef, has already been attempted to be explained, when giving the proofs of the recent

elevation of this island. In Cook's charts the little outlying island also of EOAIGEE, is represented as

fringed; coloured red.EOUA. I cannot make out from Captain Cook's charts and descriptions, that this

island has any reef, although the bottom of the neighbouring sea seems to be corally, and the island itself is

formed of coralrock. Forster, however, distinctly ("Observations," page 14) classes it with high islands

having reefs, but it certainly is not encircled by a barrierreef and the younger Forster ("Voyage," volume i.,

page 426) says, that "a bed of coralrocks surrounded the coast towards the landingplace." I have therefore

classed it with the fringed islands and coloured it red. The several islands lying N.W. of Tongatabou, namely

ANAMOUKA, KOMANGO, KOTOU, LEFOUGA, FOA, etc., are seen in Captain Cook's chart to be fringed

by reefs, in several of them are connected together. From the various statements in the first volume of Cook's

"Third Voyage," and especially in the fourth and sixth chapters, it appears that these reefs are of

coralformation, and certainly do not belong to the barrier class; coloured red.TOUFOA AND KAO,

forming the western part of the group, according to Forster have no reefs; the former is an active

volcano.VAVAO. There is a chart of this singularly formed island, by Espinoza: according to Mr.

Williams it consists of coralrock: the Chevalier Dillon informs me that it is not fringed; not coloured. Nor

are the islands of LATTE and AMARGURA, for I have not seen plans on a large scale of them, and do not

NIOUHA, 16 deg S., 174 deg W., or KEPPEL Island of Wallis, or COCOS Island. From a view and chart of

this island given in Wallis's "Voyage" (4to edition) it is evidently encircled by a reef; coloured blue: it is

however remarkable that BOSCAWEN Island, immediately adjoining, has no reef of any kind; uncoloured.

WALLIS Island, 13 deg S., 176 deg W., a chart and view of this island in Wallis's "Voyage" (4to edition)

shows that it is encircled. A view of it in the "Naut. Mag." July 1833, page 376, shows the same fact; blue.

ALLOUFATOU, or HORN Island, ONOUAFU, or PROBY Island, and HUNTER Islands, lie between the

The best chart of the numerous islands of this group, will be found in the "Atlas of the 'Astrolabe's' Voyage."

From this, and from the description given in the "Hydrog. Memoir," accompanying it, it appears that many of

these islands are bold and mountainous, rising to the height of between 3,000 and 4,000 feet. Most of the

islands are surrounded by reefs, lying far from the land, and outside of which the ocean appears very deep.

The "Astrolabe" sounded with ninety fathoms in several places about a mile from the reefs, and found no

bottom. Although the depth within the reef is not laid down, it is evident from several expressions, that

Captain D'Urville believes that ships could anchor within, if passages existed through the outer barriers. The

Chevallier Dillon informs me that this is the case: hence I have coloured this group blue. In the S.E. part lies

BATOA, or TURTLE Island of Cook ("Second Voyage," volume ii., page 23, and chart, 4to edition)

surrounded by a coralreef, "which in some places extends two miles from the shore;" within the reef the

water appears to be deep, and outside it is unfathomable; coloured pale blue. At the distance of a few miles,

Captain Cook (Ibid., page 24) found a circular coralreef, four or five leagues in circuit, with deep water

within; "in short, the bank wants only a few little islets to make it exactly like one of the halfdrowned isles

so often mentioned,"namely, atolls. South of Batoa, lies the high island of ONO, which appears in

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 79

Bellinghausen's "Atlas" to be encircled; as do some other small islands to the south; coloured pale blue; near

Ono, there is an annular reef, quite similar to the one just described in the words of Captain Cook; coloured

ROTOUMAH, 13 deg S., 179 deg E.From the chart in Duperrey's "Atlas," I thought this island was

encircled, and had coloured it blue, but the Chevallier Dillon assures me that the reef is only a shore or

INDEPENDENCE Island, 10 deg S., 179 deg E., is described by Mr. G. Bennett, ("United Service Journal,"

1831, part ii., page 197) as a low island of coralformation, it is small, and does not appear to contain a

lagoon, although an opening through the reef is referred to. A lagoon probably once existed, and has since

OSCAR, PEYSTER, and ELLICE Islands are figured in Arrowsmith's "Chart of the Pacific" (corrected to

1832) as atolls, and are said to be very low; blue.NEDERLANDISCH Island. I am greatly indebted to the

kindness of Admiral Krusenstern, for sending me the original documents concerning this island. From the

plans given by Captains Eeg and Khremtshenko, and from the detailed account given by the former, it

appears that it is a narrow coralisland, about two miles long, containing a small lagoon. The sea is very deep

close to the shore, which is fronted by sharp coralrocks. Captain Eeg compares the lagoon with that of other

coralislands; and he distinctly says, the land is "very low." I have therefore coloured it blue. Admiral

Krusenstern ("Memoir on the Pacific," Append., 1835) states that its shores are eighty feet high; this probably

arose from the height of the cocoanut trees, with which it is covered, being mistaken for land. GRAN

COCAL is said in Krusenstern's "Memoir," to be low, and to be surrounded by a reef; it is small, and

therefore probably once contained a lagoon; uncoloured.ST. AUGUSTIN. From a chart and view of it,

given in the "Atlas of the 'Coquille's' Voyage," it appears to be a small atoll, with its lagoon partly filled up;

The chart of this group, given in the "Atlas of the 'Coquille's' Voyage," at once shows that it is composed of

ten well characterised atolls. In D'Urville and Lottin's chart, SYDENHAM is written with a capital letter,

signifying that it is high; but this certainly is not the case, for it is a perfectly characterised atoll, and a sketch,

showing how low it is, is given in the "'Coquille's' Atlas." Some narrow striplike reefs project from the

southern side of DRUMMOND atoll, and render it irregular. The southern island of the group is called

CHASE (in some charts, ROTCHES); of this I can find no account, but Mr. F.D. Bennett discovered

("Geographical Journal", volume vii., page 229), a low extensive island in nearly the same latitude, about

three degrees westward of the longitude assigned to Rotches, but very probably it is the same island. Mr.

Bennett informs me that the man at the masthead reported an appearance of lagoonwater in the centre; and,

therefore, considering its position, I have coloured it blue. PITT Island, at the extreme northern point of

the group, is left uncoloured, as its exact position and nature is not known.BYRON Island, which lies a

little to the eastward, does not appear to have been visited since Commodore Byron's voyage, and it was then

OCEAN, PLEASANT, and ATLANTIC Islands all lie considerably to the west of the Gilbert group: I have

been unable to find any distinct account of them. Ocean Island is written with small letters in the French

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 80

We are well acquainted with this group from the excellent charts of the separate islands, made during the two

voyages of Kotzebue: a reduced one of the whole group may be easily seen in Krusenstern's "Atlas," and in

Kotzebue's "Second Voyage." The group consists (with the exception of two LITTLE islands which probably

have had their lagoon filled up) of a double row of twentythree large and wellcharacterised atolls, from the

examination of which Chamisso has given us his wellknown account of coralformations. I include

GASPAR RICO, or CORNWALLIS Island in this group, which is described by Chamisso (Kotzebue's "First

Voyage," volume iii., page 179) "as a low sickleformed group, with mould only on the windward side."

Gaspard Island is considered by some geographers as a distinct island lying N.E. of the group, but it is not

entered in the chart by Krusenstern; left uncoloured. In the S.W. part of this group lies BARING Island, of

which little is known (see Krusenstern's "Appendix," 1835, page 149). I have left it uncoloured; but

BOSTON Island I have coloured blue, as it is described (Ibid.) as consisting of fourteen small islands, which,

no doubt, enclose a lagoon, as represented in a chart in the "'Coquille's' Atlas."Two islands, AUR KAWEN

and GASPAR RICO, are written in the French chart with capital letters; but this is an error, for from the

account given by Chamisso in Kotzebue's "First Voyage," they are certainly low. The nature, position, and

even existence, of the shoals and small islands north of the Marshall group, are doubtful.

Any chart, on even a small scale, of these islands, will show that their shores are almost without reefs,

presenting a remarkable contrast with those of New Caledonia on the one hand, and the Fidji group on the

other. Nevertheless, I have been assured by Mr. G. Bennett, that coral grows vigorously on their shores; as

indeed, will be further shown in some of the following notices. As, therefore, these islands are not encircled,

and as coral grows vigorously on their shores, we might almost conclude, without further evidence, that they

were fringed, and hence I have applied the red colour with rather greater freedom than in other

instances.MATTHEW'S ROCK, an active volcano, some way south of the group (of which a plan is given

in the "Atlas of the 'Astrolabe's' Voyage") does not appear to have reefs of any kind about it.ANNATOM,

the southernmost of the Hebrides; from a rough woodcut given in the "United Service Journal" (1831, part

iii., page 190), accompanying a paper by Mr. Bennett, it appears that the shore is fringed; coloured

red.TANNA. Forster, in his "Observations" (page 22), says Tanna has on its shores coralrock and

madrepores; and the younger Forster, in his account (volume ii., page 269) speaking of the harbour says, the

whole S.E. side consists of coralreefs, which are overflowed at highwater; part of the southern shore in

Cook's chart is represented as fringed; coloured red.IMMER is described ("United Service Journal," 1831,

part iii., page 192) by Mr. Bennett as being of moderate elevation, with cliffs appearing like sandstone: coral

grows in patches on its shore, but I have not coloured it; and I mention these facts, because Immer might have

been thought from Forster's classification ("Observations," page 14), to have been a low island or even an

atoll. ERROMANGO Island; Cook ("Second Voyage," volume ii., page 45, 4to edition) speaks of rocks

everywhere LINING the coast, and the natives offered to haul his boat over the breakers to the sandy beach:

Mr. Bennett, in a letter to the Editor of the "Singapore Chron.," alludes to the REEFS on its shores. It may, I

think, be safely inferred from these passages that the shore is fringed in parts by coralreefs; coloured

red.SANDWICH Island. The east coast is said (Cook's "Second Voyage," volume ii., page 41) to be low,

and to be guarded by a chain of breakers. In the accompanying chart it is seen to be fringed by a reef;

coloured red.MALLICOLLO. Forster speaks of the reefbounded shore: the reef is about thirty yards

wide, and so shallow that a boat cannot pass over it. Forster also ("Observations," page 23) says, that the

rocks of the seashore consist of madrepore. In the plan of Sandwich harbour, the headlands are represented

as fringed; coloured red.AURORA and PENTECOST Islands, according to Bougainville, apparently have

no reefs; nor has the large island of S. ESPIRITU, nor BLIGH Island or BANKS' Islands, which latter lie to

the N.E. of the Hebrides. But in none of these cases, have I met with any detailed account of their shores, or

seen plans on a large scale; and it will be evident, that a fringingreef of only thirty or even a few hundred

yards in width, is of so little importance to navigation, that it will seldom be noticed, excepting by chance;

and hence I do not doubt that several of these islands, now left uncoloured, ought to be red.

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 81

VANIKORO (Figure 1, Plate I.) offers a striking example of a barrierreef: it was first described by the

Chevalier Dillon, in his voyage, and was surveyed in the "Astrolabe"; coloured pale blue.TIKOPIA and

FATAKA Islands appear, from the descriptions of Dillon and D'Urville, to have no reefs; ANOUDA is a low,

flat island, surrounded by cliffs ("'Astrolabe' Hydrog." and Krusenstern, "Mem." volume ii., page 432); these

are uncoloured. TOUPOUA (OTOOBOA of Dillon) is stated by Captain Tromelin ("Annales Marit." 1829,

page 289) to be almost entirely included in a reef, lying at the distance of two miles from the shore. There is a

space of three miles without any reef, which, although indented with bays, offers no anchorage from the

extreme depth of the water close to the shore: Captain Dillon also speaks of the reefs fronting this island;

coloured blue. SANTACRUZ. I have carefully examined the works of Carteret, D'Entrecasteaux, Wilson,

and Tromelin, and I cannot discover any mention of reefs on its shores; left uncoloured.TINAKORO is a

constantly active volcano without reefs.MENDANA ISLES (mentioned by Dillon under the name of

MAMMEE, etc.); said by Krusenstern to be low, and intertwined with reefs. I do not believe they include a

lagoon; I have left them uncoloured.DUFF'S Islands compose a small group directed in a N.W. and S.E.

band; they are described by Wilson (page 296, "Miss. Voy." 4to edition), as formed by boldpeaked land,

with the islands surrounded by coralreefs, extending about half a mile from the shore; at a distance of a mile

from the reefs he found only seven fathoms. As I have no reason for supposing there is deep water within

these reefs, I have coloured them red. KENNEDY Island, N.E. of Duff's. I have been unable to find any

The great barrierreefs on the shores of this island have already been described (Figure 5, Plate II.). They

have been visited by Labillardiere, Cook, and the northern point by D'Urville; this latter part so closely

resembles an atoll that I have coloured it dark blue. The LOYALTY group is situated eastward of this island;

from the chart and description given in the "Voyage of the 'Astrolabe'," they do not appear to have any reefs;

north of this group, there are some extensive low reefs (called ASTROLABE and BEAUPRE,) which do not

The limits of this great reef, which has already been described, have been coloured from the charts of

Flinders and King. In the northern parts, an atollformed reef, lying outside the barrier, has been described by

Bligh, and is coloured dark blue. In the space between Australia and New Caledonia, called by Flinders the

Corallian Sea, there are numerous reefs. Of these, some are represented in Krusenstern's "Atlas" as having an

atolllike structure; namely, BAMPTON shoal, FREDERIC, VINE or Horseshoe, and ALERT reefs; these

The dangerous reefs which front and surround the western, southern, and northern coasts of this socalled

peninsula and archipelago, seem evidently to belong to the barrier class. The land is lofty, with a low fringe

on the coast; the reefs are distant, and the sea outside them profoundly deep. Nearly all that is known of this

group is derived from the labours of D'Entrecasteaux and Bougainville: the latter has represented one

continuous reef ninety miles long, parallel to the shore, and in places as much as ten miles from it; coloured

pale blue. A little distance northward we have the LAUGHLAN Islands, the reefs round which are engraved

in the "Atlas of the Voyage of the 'Astrolabe'," in the same manner as in the encircled islands of the Caroline

Archipelago, the reef is, in parts, a mile and a half from the shore, to which it does not appear to be attached;

coloured blue. At some little distance from the extremity of the Louisiade lies the WELLS reef, described in

G. Hamilton's "Voyage in H.M.S. 'Pandora'" (page 100): it is said, "We found we had got embayed in a

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 82

double reef, which will soon be an island." As this statement is only intelligible on the supposition of the reef

being crescent or horseshoe formed, like so many other submerged annular reefs, I have ventured to colour

The chart in Krusenstern's "Atlas" shows that these islands are not encircled, and as coral appears from the

works of Surville, Bougainville, and Labillardiere, to grow on their shores, this circumstance, as in the case

of the New Hebrides, is a presumption that they are fringed. I cannot find out anything from

D'Entrecasteaux's "Voyage," regarding the southern islands of the group, so have left them

uncoloured.MALAYTA Island in a rough MS. chart in the Admiralty has its northern shore

fringed.YSABEL Island, the N.E. part of this island, in the same chart, is also fringed: Mendana, speaking

(Burney, volume i., page 280) of an islet adjoining the northern coast, says it is surrounded by reefs; the

shores, also of Port Praslin appear regularly fringed.CHOISEUL Island. In Bougainville's "Chart of

Choiseul Bay," parts of the shores are fringed by coralreefs. BOUGAINVILLE Island. According to

D'Entrecasteaux the western shore abounds with coralreefs, and the smaller islands are said to be attached to

the larger ones by reefs; all the beforementioned islands have been coloured red.BOUKA Islands.

Captain Duperrey has kindly informed me in a letter that he passed close round the northern side of this

island (of which a plan is given in his "Atlas of the 'Coquille's' Voyage"), and that it was "garnie d'une bande

de recifs a fleur d'eau adherentes au rivage;" and he infers, from the abundance of coral on the islands north

Off the north coast of the Solomon Archipelago there are several small groups which are little known; they

appear to be low, and of coralformation; and some of them probably have an atolllike structure; the

Chevallier Dillon, however, informs me that this is not the case with the B. de CANDELARIA.OUTONG

JAVA, according to the Spanish navigator, Maurelle, is thus characterised; but this is the only one which I

The shores of the S.W. point of this island and some adjoining islets, are fringed by reefs, as may be seen in

the "Atlases of the Voyages of the 'Coquille' and 'Astrolabe'." M. Lesson observes that the reefs are open in

front of each streamlet. The DUKE OF YORK'S Island is also fringed; but with regard to the other parts of

NEW IRELAND, NEW HANOVER, and the small islands lying northward, I have been unable to obtain any

information. I will only add that no part of New Ireland appears to be fronted by distant reefs. I have coloured

From the charts in the "Voyage of the 'Astrolabe'," and from the "Hydrog. Memoir," it appears that these

coasts are entirely without reefs, as are the SCHOUTEN Islands, lying close to the northern shore of New

Guinea. The western and southwestern parts of New Guinea, will be treated of when we come to the islands

From the accounts by Bougainville, Maurelle, D'Entrecasteaux, and the scattered notices collected by

Horsburgh, it appears, that some of the many islands composing it, are high, with a bold outline; and others

are very low, small and interlaced with reefs. All the high islands appear to be fronted by distant reefs rising

abruptly from the sea, and within some of which there is reason to believe that the water is deep. I have

therefore little doubt they are of the barrier class.In the southern part of the group we have ELIZABETH

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 83

Island, which is surrounded by a reef at the distance of a mile; and two miles eastward of it (Krusenstern,

"Append." 1835, page 42) there is a little island containing a lagoon.Near here, also lies

CIRCULARREEF (Horsburgh, "Direct." volume i., page 691, 4th edition), "three or four miles in diameter

having deep water inside with an opening at the N.N.W. part, and on the outside steep to." I have from these

ECHEQUIER, and HERMITES, consist of innumerable low islands of coralformation, which probably have

atolllike forms; but not being able to ascertain this, I have not coloured them, nor DUROUR Island, which

The CAROLINE ARCHIPELAGO is now wellknown, chiefly from the hydrographical labours of Lutke; it

contains about forty groups of atolls, and three encircled islands, two of which are engraved in Figures 2 and

7, Plate I. Commencing with the eastern part; the encircling reef round UALEN appears to be only about half

a mile from the shore; but as the land is low and covered with mangroves ("Voyage autour du Monde," par F.

Lutke, volume i., page 339), the real margin has not probably been ascertained. The extreme depth in one of

the harbours within the reef is thirtythree fathoms (see charts in "Atlas of 'Coquille's' Voyage"), and outside

at half a mile distant from the reef, no bottom was obtained with two hundred and fifty fathoms. The reef is

surmounted by many islets, and the lagoonlike channel within is mostly shallow, and appears to have been

much encroached on by the low land surrounding the central mountains; these facts show that time has

allowed much detritus to accumulate; coloured pale blue. POUYNIPETE, or Seniavine. In the greater part

of the circumference of this island, the reef is about one mile and three quarters distant; on the north side it is

five miles off the included high islets. The reef is broken in several places; and just within it, the depth in one

place is thirty fathoms, and in another, twentyeight, beyond which, to all appearance, there was "un porte

vaste et sur" (Lutke, volume ii., page 4); coloured pale blue.HOGOLEU or ROUG. This wonderful group

contains at least sixtytwo islands, and its reef is one hundred and thirtyfive miles in circuit. Of the islands,

only a few, about six or eight (see "Hydrog. Descrip." page 428, of the "Voyage of the 'Astrolabe'," and the

large accompanying chart taken chiefly from that given by Duperrey) are high, and the rest are all small, low,

and formed on the reef. The depth of the great interior lake has not been ascertained; but Captain D'Urville

appears to have entertained no doubt about the possibility of taking in a frigate. The reef lies no less than

fourteen miles distant from the northern coasts of the interior high islands, seven from their western sides,

and twenty from the southern; the sea is deep outside. This island is a likeness on a grand scale to the

Gambier group in the Low Archipelago. Of the groups of low (In D'Urville and Lottin's chart, Peserare is

written with capital letters; but this evidently is an error, for it is one of the low islets on the reef of

Namonouyto (see Lutke's charts)a regular atoll.) islands forming the chief part of the Caroline

Archipelago, all those of larger size, have the true atollstructure (as may be seen in the "Atlas" by Captain

Lutke), and some even of the very small ones, as MACASKILL and DUPERREY, of which plans are given

in the "Atlas of the 'Coquille's' Voyage." There are, however, some low small islands of coralformation,

namely OLLAP, TAMATAM, BIGALI, SATAHOUAL, which do not contain lagoons; but it is probable that

lagoons originally existed, but have since filled up: Lutke (volume ii., page 304) seems to have thought that

all the low islands, with only one exception, contained lagoons. From the sketches, and from the manner in

which the margins of these islands are engraved in the "Atlas of the Voyage of the 'Coquille'," it might have

been thought that they were not low; but by a comparison with the remarks of Lutke (volume ii., page 107,

regarding Bigali) and of Freycinet ("Hydrog. Memoir 'L'Uranie' Voyage," page 188, regarding Tamatam,

Ollap, etc.), it will be seen that the artist must have represented the land incorrectly. The most southern island

in the group, namely PIGUIRAM, is not coloured, because I have found no account of it. NOUGOUOR, or

MONTE VERDISON, which was not visited by Lutke, is described and figured by Mr. Bennett ("United

Service Journal," January 1832) as an atoll. All the abovementioned islands have been coloured blue.

FAIS Island is ninety feet high, and is surrounded, as I have been informed by Admiral Lutke, by a narrow

reef of living coral, of which the broadest part, as represented in the charts, is only 150 yards; coloured

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 84

red. PHILIP Island., I believe, is low; but Hunter, in his "Historical Journal," gives no clear account of it;

uncoloured.ELIVI; from the manner in which the islets on the reefs are engraved, in the "Atlas of the

'Astrolabe's' Voyage," I should have thought they were above the ordinary height, but Admiral Lutke assures

me this is not the case: they form a regular atoll; coloured blue.GOUAP (EAP of Chamisso), is a high

island with a reef (see chart in "Voyage of the 'Astrolabe'"), more than a mile distant in most parts from the

shore, and two miles in one part. Captain D'Urville thinks that there would be anchorage ("Hydrog. Descript.

'Astrolabe' Voyage," page 436) for ships within the reef, if a passage could be found; coloured pale

blue.GOULOU, from the chart in the "'Astrolabe's' Atlas," appears to be an atoll. D'Urville ("Hydrog.

Krusenstern speaks of some of the islands being mountainous; the reefs are distant from the shore, and there

are spaces within them, and not opposite valleys, with from ten to fifteen fathoms. According to a MS. chart

of the group by Lieutenant Elmer in the Admiralty, there is a large space within the reef with deepish water;

although the high land does not hold a central position with respect to the reefs, as is generally the case, I

have little doubt that the reefs of the Pelew Islands ought to be ranked with the barrier class, and I have

coloured them pale blue. In Lieutenant Elmer's chart there is a horseshoeformed shoal, laid down thirteen

miles N.W. of Pelew, with fifteen fathoms within the reef, and some dry banks on it; coloured dark

blue.SPANISH, MARTIRES, SANSEROT, PULO ANNA and MARIERE Islands are not coloured,

because I know nothing about them, excepting that according to Krusenstern, the second, third, and fourth

mentioned, are low, placed on coralreefs, and therefore, perhaps, contain lagoons; but Pulo Mariere is a

GUAHAN. Almost the whole of this island is fringed by reefs, which extend in most parts about a third of a

mile from the land. Even where the reefs are most extensive, the water within them is shallow. In several

parts there is a navigable channel for boats and canoes within the reefs. In Freycinet's "Hydrog. Mem." there

is an account of these reefs, and in the "Atlas," a map on a large scale; coloured red.ROTA. "L'ile est

presque entierement entouree des recifs" (page 212, Freycinet's "Hydrog. Mem."). These reefs project about a

quarter of a mile from the shore; coloured red.TINIAN. THE EASTERN coast is precipitous, and is

without reefs; but the western side is fringed like the last island; coloured red.SAYPAN. The N.E. coast,

and likewise the western shores appear to be fringed; but there is a great, irregular, hornlike reef projecting

far from this side; coloured red.FARALLON DE MEDINILLA, appears so regularly and closely fringed in

Freycinet's charts, that I have ventured to colour it red, although nothing is said about reefs in the

"Hydrographical Memoir." The several islands which form the northern part of the group are volcanic (with

the exception perhaps of Torres, which resembles in form the madreporitic island of Medinilla), and appear to

be without reefs.MANGS, however, is described (by Freycinet, page 219, "Hydrog.") from some Spanish

charts, as formed of small islands placed "au milieu des nombreux recifs;" and as these reefs in the general

chart of the group do not project so much as a mile; and as there is no appearance from a double line, of the

existence of deep water within, I have ventured, although with much hesitation, to colour them red.

Respecting FOLGER and MARSHALL Islands which lie some way east of the Marianas, I can find out

nothing, excepting that they are probably low. Krusenstern says this of Marshall Island; and Folger Island is

PEEL Island has been examined by Captain Beechey, to whose kindness I am much indebted for giving me

information regarding it: "At Port Lloyd there is a great deal of coral; and the inner harbour is entirely formed

by coralreefs, which extend outside the port along the coast." Captain Beechey, in another part of his letter

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 85

to me, alludes to the reefs fringing the island in all directions; but at the same time it must be observed that

the surf washes the volcanic rocks of the coast in the greater part of its circumference. I do not know whether

the other islands of the Archipelago are fringed; I have coloured Peel Island red.GRAMPUS Island to the

eastward, does not appear (Meare's "Voyage," page 95) to have any reefs, nor does ROSARIO Island (from

Lutke's chart), which lies to the westward. Respecting the few other islands in this part of the sea, namely the

SULPHUR Islands, with an active volcano, and those lying between Bonin and Japan (which are situated

near the extreme limit in latitude, at which reefs are formed), I have not been able to find any clear account.

PORT DORY. From the charts in the "Voyage of the 'Coquille'," it would appear that the coast in this part is

fringed by coralreefs; M. Lesson, however, remarks that the coral is sickly; coloured red.WAIGIOU. A

considerable portion of the northern shores of these islands is seen in the charts (on a large scale) in

Freycinet's "Atlas" to be fringed by coralreefs. Forrest (page 21, "Voyage to New Guinea") alludes to the

coralreefs lining the heads of Piapis Bay; and Horsburgh (volume ii., page 599, 4th edition), speaking of the

islands in Dampier Strait, says "sharp coralrocks line their shores;" coloured red.In the sea north of these

islands, we have GUEDES (or FREEWILL, or ST. DAVID'S), which from the chart given in the 4to edition

of Carteret's "Voyage," must be an atoll. Krusenstern says the islets are very low; coloured

blue.CARTERET'S SHOALS, in 2 deg 53' N., are described as circular, with stony points showing all

round, with deeper water in the middle; coloured blue.AIOU; the plan of this group, given in the "Atlas of

the Voyage of the 'Astrolabe'," shows that it is an atoll; and, from a chart in Forrest's "Voyage," it appears

that there is twelve fathoms within the circular reef; coloured blue.The S.W. coast of New Guinea appears

to be low, muddy, and devoid of reefs. The ARRU, TIMORLAUT, and TENIMBER groups have lately

been examined by Captain Kolff, the MS. translation of which, by Mr. W. Earl, I have been permitted to read,

through the kindness of Captain Washington, R.N. These islands are mostly rather low, and are surrounded

by distant reefs (the Ki Islands, however, are lofty, and, from Mr. Stanley's survey, appear without reefs); the

sea in some parts is shallow, in others profoundly deep (as near Larrat). From the imperfection of the

published charts, I have been unable to decide to which class these reefs belong. From the distance to which

they extend from the land, where the sea is very deep, I am strongly inclined to believe they ought to come

within the barrier class, and be coloured blue; but I have been forced to leave them uncoloured.The

lastmentioned groups are connected with the east end of Ceram by a chain of small islands, of which the

small groups of CERAMLAUT, GORAM and KEFFING are surrounded by very extensive reefs, projecting

into deep water, which, as in the last case, I strongly suspect belong to the barrier class; but I have not

coloured them. From the south side of Keffing, the reefs project five miles (Windsor Earl's "Sailing Direct.

In various charts which I have examined, several parts of the coast are represented as fringed by

reefs.MANIPA Island, between Ceram and Bourou, in an old MS. chart in the Admiralty, is fringed by a

very irregular reef, partly dry at low water, which I do not doubt is of coralformation; both islands coloured

red.BOUROU; parts of this island appear fringed by coralreefs, namely, the eastern coast, as seen in

Freycinet's chart; and CAJELI BAY, which is said by Horsburgh (volume ii., page 630) to be lined by

coralreefs, that stretch out a little way, and have only a few feet water on them. In several charts, portions of

the islands forming the AMBOINA GROUP are fringed by reefs; for instance, NOESSA, HARENCA, and

UCASTER, in Freycinet's charts. The abovementioned islands have been coloured red, although the

evidence is not very satisfactory.North of Bourou the parallel line of the XULLA Isles extends: I have not

been able to find out anything about them, excepting that Horsburgh (volume ii., page 543) says that the

northern shore is surrounded by a reef at the distance of two or three miles; uncoloured.MYSOL GROUP;

the Kanary Islands are said by Forrest ("Voyage," page 130) to be divided from each other by deep straits,

and are lined with coralrocks; coloured red.GUEBE, lying between Waigiou and Gilolo, is engraved as if

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 86

fringed; and it is said by Freycinet, that all the soundings under five fathoms were on coral; coloured

red.GILOLO. In a chart published by Dalrymple, the numerous islands on the western, southern

(BATCHIAN and the STRAIT OF PATIENTIA), and eastern sides appear fringed by narrow reefs; these

reefs, I suppose, are of coral, for it is said in "Malte Brun" (volume xii., page 156), "Sur les cotes (of

Batchian) comme DANS LES PLUPART des iles de cet archipel, il y a de rocs de medrepores d'une beaute et

d'une variete infimies." Forrest, also (page 50), says Seland, near Batchian, is a little island with reefs of

coral; coloured red.MORTY Island (north of Gilolo). Horsburgh (volume ii., page 506) says the northern

coast is lined by reefs, projecting one or two miles, and having no soundings close to them; I have left it

uncoloured, although, as in some former cases, it ought probably to be pale blue.CELEBES. The western

and northern coasts appear in the charts to be bold and without reefs. Near the extreme northern point,

however, an islet in the STRAITS OF LIMBE, and parts of the adjoining shore, appear to be fringed: the east

side of the bay of MANADO, has deep water, and is fringed by sand and coral ("'Astrol.' Voyage," Hydrog.

Part, pages 4534); this extreme point, therefore, I have coloured red.Of the islands leading from this point

to Magindanao, I have not been able to find any account, except of SERANGANI, which appears surrounded

by narrow reefs; and Forrest ("Voyage," page 164) speaks of coral on its shores; I have, therefore, coloured

this island red. To the eastward of this chain lie several islands; of which I cannot find any account, except of

KARKALANG, which is said by Horsburgh (volume ii., page 504) to be lined by a dangerous reef,

The account of the following islands is taken from Captain D. Kolff's "Voyage," in 1825, translated by Mr.

W. Earl, from the Dutch.LETTE has "reefs extending along shore at the distance of half a mile from the

land."MOA has reefs on the S.W. part.LAKOR has a reef lining its shore; these islands are coloured

red.Still more eastward, LUAN has, differently from the lastmentioned islands, an extensive reef; it is

steep outside, and within there is a depth of twelve feet; from these facts, it is impossible to decide to which

class this island belongs.KISSA, off the point of Timor, has its "shore fronted by a reef, steep too on the

outer side, over which small proahs can go at the time of high water;" coloured red.TIMOR; most of the

points, and some considerable spaces of the northern shore, are seen in Freycinet's chart to be fringed by

coralreefs; and mention is made of them in the accompanying "Hydrog. Memoir;" coloured red.SAVU,

S.E. of Timor, appears in Flinders' chart to be fringed; but I have not coloured it, as I do not know that the

reefs are of coral. SANDALWOOD Island has, according to Horsburgh (volume ii., page 607), a reef on

its southern shore, four miles distant from the land; as the neighbouring sea is deep, and generally bold, this

It appears, in Captain King's Sailing Directions ("Narrative of Survey," volume ii, pages 325369), that there

are many extensive coralreefs skirting, often at considerable distances, the N.W. shores, and encompassing

the small adjoining islets. Deep water, in no instance, is represented in the charts between these reefs and the

land; and, therefore, they probably belong to the fringing class. But as they extend far into the sea, which is

generally shallow, even in places where the land seems to be somewhat precipitous; I have not coloured

them. Houtman's Abrolhos (latitude 28 deg S. on west coast) have lately been surveyed by Captain Wickham

(as described in "Naut. Mag." 1841, page 511): they lie on the edge of a steeply shelving bank, which extends

about thirty miles seaward, along the whole line of coast. The two southern reefs, or islands, enclose a

lagoonlike space of water, varying in depth from five to fifteen fathoms, and in one spot with twentythree

fathoms. The greater part of the island has been formed on their inland sides, by the accumulation of

fragments of coral; the seaward face consisting of nearly bare ledges of rock. Some of the specimens, brought

home by Captain Wickham, contained fragments of marine shells, but others did not; and these closely

resembled a formation at King George's Sound, principally due to the action of the wind on calcareous dust,

which I shall describe in a forthcoming part. From the extreme irregularity of these reefs with their lagoons,

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 87

and from their position on a bank, the usual depth of which is only thirty fathoms, I have not ventured to class

them with atolls, and hence have left them uncoloured.ROWLEY SHOALS. These lie some way from the

N.W. coast of Australia: according to Captain King ("Narrative of Survey," volume i., page 60), they are of

coralformation. They rise abruptly from the sea, and Captain King had no bottom with 170 fathoms close to

them. Three of them are crescentshaped; they are mentioned by Mr. Lyell, on the authority of Captain King,

with reference to the direction of their open sides. "A third oval reef of the same group is entirely submerged"

("Principles of Geology," book iii. chapter xviii.); coloured blue.SCOTT'S REEFS, lying north of Rowley

Shoals, are briefly described by Captain Wickham ("Naut. Mag." 1841, page 440): they appear to be of great

size, of a circular form, and "with smooth water within, forming probably a lagoon of great extent." There is a

break on the western side, where there probably is an entrance: the water is very deep off these reefs;

Proceeding westward along the great volcanic chain of the East Indian Archipelago, SOLOR STRAIT is

represented in a chart published by Dalrymple from a Dutch MS., as fringed; as are parts of FLORES, of

ADENARA, and of SOLOR. Horsburgh speaks of coral growing on these shores; and therefore I have no

doubt that the reefs are of coral, and accordingly have coloured them red. We hear from Horsburgh (volume

ii., page 602) that a coralflat bounds the shores of SAPY Bay. From the same authority it appears (page 610)

that reefs fringe the island of TIMORYOUNG, on the N. shore of Sumbawa; and, likewise (page 600), that

BALLY town in LOMBOCK, is fronted by a reef, stretching along the shore at a distance of a hundred

fathoms, with channels through it for boats; these places, therefore, have been coloured red.BALLY

Island. In a Dutch MS. chart on a large scale of Java, which was brought from that island by Dr. Horsfield,

who had the kindness to show it me at the India House, its western, northern, and southern shores appear very

regularly fringed by a reef (see also Horsburgh, volume ii., page 593); and as coral is found abundantly there,

I have not the least doubt that the reef is of coral, and therefore have coloured it red.

My information regarding the reefs of this great island is derived from the chart just mentioned. The greater

part of MADUARA is represented in it as regularly fringed, and likewise portions of the coast of Java

immediately south of it. Dr. Horsfield informs me that coral is very abundant near SOURABAYA. The islets

and parts of the N. coast of Java, west of POINT BUANG, or JAPARA, are fringed by reefs, said to be of

coral. LUBECK, or BAVIAN Islands, lying at some distance from the shore of Java, are regularly fringed by

coralreefs. CARIMON JAVA appears equally so, though it is not directly said that the reefs are of coral;

there is a depth between thirty and forty fathoms round these islands. Parts of the shores of SUNDA STRAIT,

where the water is from forty to eighty fathoms deep, and the islets near BATAVIA appear in several charts

to be fringed. In the Dutch chart the southern shore, in the narrowest part of the island, is in two places

fringed by reefs of coral. West of SEGORROWODEE Bay, and the extreme S.E. and E. portions are likewise

The EAST COAST OF Borneo appears, in most parts, free from reefs, and where they occur, as on the east

coast of PAMAROONG, the sea is very shallow; hence no part is coloured. In MACASSAR Strait itself, in

about latitude 2 deg S., there are many small islands with coralshoals projecting far from them. There are

also (old charts by Dalrymple) numerous little flats of coral, not rising to the surface of the water, and

shelving suddenly from five fathoms to no bottom with fifty fathoms; they do not appear to have a

lagoonlike structure. There are similar coralshoals a little farther south; and in latitude 4 deg 55' there are

two, which are engraved from modern surveys, in a manner which might represent an annular reef with deep

water inside: Captain Moresby, however, who was formerly in this sea, doubts this fact, so that I have left

them uncoloured: at the same time I may remark, that these two shoals make a nearer approach to the

atolllike structure than any other within the E. Indian Archipelago. Southward of these shoals there are other

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 88

low islands and irregular coralreefs; and in the space of sea, north of the great volcanic chain, from Timor to

Java, we have also other islands, such as the POSTILLIONS, KALATOA, TOKANBESSEES, etc., which

are chiefly low, and are surrounded by very irregular and distant reefs. From the imperfect charts I have seen,

I have not been able to decide whether they belong to the atoll or barrierclasses, or whether they merely

fringe submarine banks, and gently sloping land. In the Bay of BONIN, between the two southern arms of

Celebes, there are numerous coral reefs; but none of them seem to have an atolllike structure. I have,

therefore, not coloured any of the islands in this part of the sea; I think it, however, exceedingly probable that

some of them ought to be blue. I may add that there is a harbour on the S.E. coast of BOUTON which,

according to an old chart, is formed by a reef, parallel to the shore, with deep water within; and in the

"Voyage of the 'Coquille'," some neighbouring islands are represented with reefs a good way distant, but I do

not know whether with deep water within. I have not thought the evidence sufficient to permit me to colour

Commencing with the west coast and outlying islands, ENGANO Island is represented in the published chart

as surrounded by a narrow reef, and Napier, in his "Sailing Directions," speaks of the reef being of coral (also

Horsburgh, volume ii., page 115); coloured red.RAT Island (3 deg 51' S.) is surrounded by reefs of coral,

partly dry at low water, (Horsburgh, volume ii., page 96).TRIESTE Island (4 deg 2' S.). The shore is

represented in a chart which I saw at the India House, as fringed in such a manner, that I feel sure the fringe

consists of coral; but as the island is so low, that the sea sometimes flows quite over it (Dampier, "Voyage,"

volume i., page 474), I have not coloured it.PULO DOOA (latitude 3 deg). In an old chart it is said there

are chasms in the reefs round the island, admitting boats to the wateringplace, and that the southern islet

consists of a mass of sand and coral.PULO PISANG; Horsburgh (volume ii., page 86) says that the rocky

coralbank, which stretches about forty yards from the shore, is steep to all round: in a chart, also, which I

have seen, the island is represented as regularly fringed.PULO MINTAO is lined with reefs on its west

side (Horsburgh, volume ii., page 107).PULO BANIAK; the same authority (volume ii., page 105),

speaking of a part, says it is faced with coralrocks.MINGUIN (3 deg 36' N.). A coralreef fronts this

place, and projects into the sea nearly a quarter of a mile ("Notices of the Indian Arch." published at

Singapore, page 105).PULO BRASSA (5 deg 46' N.). A reef surrounds it at a cable's length (Horsburgh,

volume ii., page 60). I have coloured all the abovespecified points red. I may here add, that both Horsburgh

and Mr. Moor (in the "Notices" just alluded to) frequently speak of the numerous reefs and banks of coral on

the west coast of Sumatra; but these nowhere have the structure of a barrierreef, and Marsden ("History of

Sumatra") states, that where the coast is flat, the fringingreefs extend furthest from it. The northern and

southern points, and the greater part of the east coast, are low, and faced with mud banks, and therefore

The chart represents the islands of this group as fringed by reefs. With regard to GREAT NICOBAR, Captain

Moresby informs me, that it is fringed by reefs of coral, extending between two and three hundred yards from

the shore. The NORTHERN NICOBARS appear so regularly fringed in the published charts, that I have no

From an examination of the MS. chart, on a large scale, of this island, by Captain Arch. Blair, in the

Admiralty, several portions of the coast appear fringed; and as Horsburgh speaks of coralreefs being

numerous in the vicinity of these islands, I should have coloured them red, had not some expressions in a

paper in the "Asiatic Researches" (volume iv., page 402) led me to doubt the existence of reefs; uncoloured.

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 89

The coast of MALACCA, TENASSERIM and the coasts northward, appear in the greater part to be low and

muddy: where reefs occur, as in parts of MALACCA STRAITS, and near SINGAPORE, they are of the

fringing kind; but the water is so shoal, that I have not coloured them. In the sea, however, between Malacca

and the west coast of Borneo, where there is a greater depth from forty to fifty fathoms, I have coloured red

some of the groups, which are regularly fringed. The northern NATUNAS and the ANAMBAS Islands are

represented in the charts on a large scale, published in the "Atlas of the Voyage of the 'Favourite'," as fringed

by reefs of coral, with very shoal water within them.TUMBELAN and BUNOA Islands (1 deg N.) are

represented in the English charts as surrounded by a very regular fringe. ST. BARBES (0 deg 15' N.) is

said by Horsburgh (volume ii., page 279) to be fronted by a reef, over which boats can land only at high

water.The shore of BORNEO at TUNJONG APEE is also fronted by a reef, extending not far from the

land (Horsburgh, volume ii., page 468). These places I have coloured red; although with some hesitation, as

the water is shallow. I might perhaps have added PULO LEAT, in Gaspar Strait, LUCEPARA, and

CARIMATA; but as the sea is confined and shallow, and the reefs not very regular, I have left them

The water shoals gradually towards the whole west coast of BORNEO: I cannot make out that it has any reefs

of coral. The islands, however, off the northern extremity, and near the S.W. end of PALAWAN, are fringed

by very distant coralreefs; thus the reefs in the case of BALABAC are no less than five miles from the land;

but the sea, in the whole of this district, is so shallow, that the reefs might be expected to extend very far from

the land. I have not, therefore, thought myself authorised to colour them. The N.E. point of Borneo, where the

water is very shoal, is connected with Magindanao by a chain of islands called the SOOLOO

ARCHIPELAGO, about which I have been able to obtain very little information; PANGOOTARAN,

although ten miles long, entirely consists of a bed of coralrock ("Notices of E. Indian Arch." page 58): I

believe from Horsburgh that the island is low; not coloured.TAHOW BANK, in some old charts, appears

like a submerged atoll; not coloured. Forrest ("Voyage," page 21) states that one of the islands near Sooloo is

surrounded by coralrocks; but there is no distant reef. Near the S. end of BASSELAN, some of the islets in

the chart accompanying Forrest's "Voyage," appear fringed with reefs; hence I have coloured, though

unwillingly, parts of the Sooloo group red. The sea between Sooloo and Palawan, near the shoal coast of

Borneo, is interspersed with irregular reefs and shoal patches; not coloured: but in the northern part of this

sea, there are two low islets, CAGAYANES and CAVILLI, surrounded by extensive coralreefs; the

breakers round the latter (Horsburgh, volume ii., page 513) extend five or six miles from a sandbank, which

forms the only dry part; these breakers are steep to outside; there appears to be an opening through them on

one side, with four or five fathoms within: from this description, I strongly suspect that Cavilli ought to be

considered an atoll; but, as I have not seen any chart of it, on even a moderately large scale, I have not

coloured it. The islets off the northern end of PALAWAN, are in the same case as those off the southern end,

namely they are fringed by reefs, some way distant from the shore, but the water is exceedingly shallow;

uncoloured. The western shore of Palawan will be treated of under the head of China Sea.

A chart on a large scale of APPOO SHOAL, which lies near the S.E. coast of Mindoro, has been executed by

Captain D. Ross: it appears atollformed, but with rather an irregular outline; its diameter is about ten miles;

there are two welldefined passages leading into the interior lagoon, which appears open; close outside the

reef all round, there is no bottom with seventy fathoms; coloured blue.MINDORO: the N.W. coast is

represented in several charts, as fringed by a reef, and LUBAN Island is said, by Horsburgh (volume ii., page

436), to be "lined by a reef."LUZON: Mr. Cuming, who has lately investigated with so much success the

Natural History of the Philippines, informs me, that about three miles of the shore north of Point St. Jago, is

fringed by a reef; as are (Horsburgh, volume ii., page 437) the Three Friars off Silanguin Bay. Between Point

Capones and Playa Honda, the coast is "lined by a coralreef, stretching out nearly a mile in some places,"

(Horsburgh); and Mr. Cuming visited some fringing reefs on parts of this coast, namely, near Puebla, Iba,

and Mansinglor. In the neighbourhood of Solonsolon Bay, the shore is lined (Horsburgh ii., page 439) by

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 90

coralreefs, stretching out a great way: there are also reefs about the islets off Solamague; and as I am

informed by Mr. Cuming, near St. Catalina, and a little north of it. The same gentleman informs me there are

reefs on the S.E. point of this island in front of Samar, extending from Malalabon to Bulusan. These appear to

be the principal fringingreefs on the coasts of Luzon; and they have all been coloured red. Mr. Cuming

informs me that none of them have deep water within; although it appears from Horsburgh that some few

extend to a considerable distance from the shore. Within the Philippine Archipelago, the shores of the islands

do not appear to be commonly fringed, with the exception of the S. shore of MASBATE, and nearly the

whole of BOHOL; which are both coloured red. On the S. shore of MAGINDANAO, Bunwoot Island is

surrounded (according to Forrest, "Voyage," page 253), by a coralreef, which in the chart appears one of the

fringing class. With respect to the eastern coasts of the whole Archipelago, I have not been able to obtain any

Horsburgh says (volume ii., page 442), coralreefs line the shores of the harbour in Fuga; and the charts

show there are other reefs about these islands. Camiguin has its shore in parts lined by coralrock

(Horsburgh, page 443); about a mile off shore there is between thirty and thirtyfive fathoms. The plan of

Port San Pio Quinto shows that its shores are fringed with coral; coloured red.BASHEE Islands:

Horsburgh, speaking of the southern part of the group (volume ii., page 445) says the shores of both islands

are fortified by a reef, and through some of the gaps in it, the natives can pass in their boats in fine weather;

the bottom near the land is coralrock. From the published charts, it is evident that several of these islands

are most regularly fringed; coloured red. The northern islands are left uncoloured, as I have been unable to

find any account of them.FORMOSA. The shores, especially the western one, seem chiefly composed of

mud and sand, and I cannot make out that they are anywhere lined by reefs; except in a harbour (Horsburgh,

volume ii., page 449) at the extreme northern point: hence, of course, the whole of this island is left

uncoloured. The small adjoining islands are in the same case. PATCHOW, or MADJIKOSIMA

GROUPS. PATCHUSON has been described by Captain Broughton ("Voy. to the N. Pacific," page 191); he

says, the boats, with some difficulty, found a passage through the coralreefs, which extend along the coast,

nearly half a mile off it. The boats were well sheltered within the reef; but it does not appear that the water is

deep there. Outside the reef the depth is very irregular, varying from five to fifty fathoms; the form of the

land is not very abrupt; coloured red.TAYPIN SAN; from the description given (page 195) by the same

author, it appears that a very irregular reef extends, to the distance of several miles, from the southern island;

but whether it encircles a space of deep water is not evident; nor, indeed, whether these outlying reefs are

connected with those more immediately adjoining the land; left uncoloured. I may here just add that the shore

of KUMI (lying west of Patchow), has a narrow reef attached to it in the plan of it, in La Peyrouse's "Atlas;"

but it does not appear in the account of the voyage that it is of coral; uncoloured.LOO CHOO. The greater

part of the coast of this moderately hilly island, is skirted by reefs, which do not extend far from the shore,

and which do not leave a channel of deep water within them, as may be seen in the charts accompanying

Captain B. Hall's voyage to Loo Choo (see also remarks in Appendix, pages xxi. and xxv.). There are,

however, some ports with deep water, formed by reefs in front of valleys, in the same manner as happens at

Mauritius. Captain Beechey, in a letter to me, compares these reefs with those encircling the Society Islands;

but there appears to me a marked difference between them, in the less distance at which the Loo Choo reefs

lie from the land with relation to the probable submarine inclination, and in the absence of an interior deep

watermoat or channel, parallel to the land. Hence, I have classed these reefs with fringingreefs, and

coloured them red.PESCADORES (west of Formosa). Dampier (volume i., page 416), has compared the

appearance of the land to the southern parts of England. The islands are interlaced with coralreefs; but as the

water is very shoal, and as spits of sand and gravel (Horsburgh, volume ii., page 450) extend far out from

them, it is impossible to draw any inferences regarding the nature of the reefs.

CHINA SEA.Proceeding from north to south, we first meet the PRATAS SHOAL (latitude 20 deg N.)

which, according to Horsburgh (volume ii., page 335), is composed of coral, is of a circular form, and has a

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 91

low islet on it. The reef is on a level with the water's edge, and when the sea runs high, there are breakers

mostly all round, "but the water within seems pretty deep in some places; although steepto in most parts

outside, there appear to be several parts where a ship might find anchorage outside the breakers;" coloured

blue.The PARACELLS have been accurately surveyed by Captain D. Ross, and charts on a large scale

published: but few low islets have been formed on these shoals, and this seems to be a general circumstance

in the China Sea; the sea close outside the reefs is very deep; several of them have a lagoonlike structure; or

separate islets (PRATTLE, ROBERT, DRUMMOND, etc.) are so arranged round a moderately shallow

space, as to appear as if they had once formed one large atoll. BOMBAY SHOAL (one of the Paracells)

has the form of an annular reef, and is "apparently deep within;" it seems to have an entrance (Horsburgh,

volume ii., page 332) on its west side; it is very steep outside.DISCOVERY SHOAL, also is of an oval

form, with a lagoonlike space within, and three openings leading into it, in which there is a depth from two

to twenty fathoms. Outside, at the distance (Horsburgh, volume ii., page 333) of only twenty yards from the

reef, soundings could not be obtained. The Paracells are coloured blue.MACCLESFIELD BANK: this is a

coralbank of great size, lying east of the Paracells; some parts of the bank are level, with a sandy bottom,

but, generally, the depth is very irregular. It is intersected by deep cuts or channels. I am not able to perceive

in the published charts (its limits, however, are not very accurately known) whether the central part is deeper,

which I suspect is the case, as in the Great Chagos Bank, in the Indian Ocean; not

coloured.SCARBOROUGH SHOAL: this coralshoal is engraved with a double row of crosses, forming a

circle, as if there was deep water within the reef: close outside there was no bottom, with a hundred fathoms;

coloured blue.The sea off the west coast of Palawan and the northern part of Borneo is strewed with

shoals: SWALLOW SHOAL, according to Horsburgh (volume ii., page 431) "is formed, LIKE MOST of the

shoals hereabouts, of a belt of coralrocks, "with a basin of deep water within."HALFMOON SHOAL

has a similar structure; Captain D. Ross describes it, as a narrow belt of coralrock, "with a basin of deep

water in the centre," and deep sea close outside.BOMBAY SHOAL appears (Horsburgh, volume ii., page

432) "to be a basin of smooth water surrounded by breakers." These three shoals I have coloured blue.The

PARAQUAS SHOALS are of a circular form, with deep gaps running through them; not coloured.A bank

gradually shoaling to the depth of thirty fathoms, extends to a distance of about twenty miles from the

northern part of BORNEO, and to thirty miles from the northern part of PALAWAN. Near the land this bank

appears tolerably free from danger, but a little further out it is thickly studded with coralshoals, which do

not generally rise quite to the surface; some of them are very steepto, and others have a fringe of

shoalwater round them. I should have thought that these shoals had level surfaces, had it not been for the

statement made by Horsburgh "that most of the shoals hereabouts are formed of a belt of coral." But, perhaps

that expression was more particularly applied to the shoals further in the offing. If these reefs of coral have a

lagoonlike structure, they should have been coloured blue, and they would have formed an imperfect barrier

in front of Palawan and the northern part of Borneo. But, as the water is not very deep, these reefs may have

grown up from inequalities on the bank: I have not coloured them.The coast of CHINA, TONQUIN, and

COCHINCHINA, forming the western boundary of the China Sea, appear to be without reefs: with regard

to the two lastmentioned coasts, I speak after examining the charts on a large scale in the "Atlas of the

SOUTH KEELING atoll has been specially described. Nine miles north of it lies North Keeling, a very small

atoll, surveyed by the "Beagle," the lagoon of which is dry at low water.CHRISTMAS Island, lying to the

east, is a high island, without, as I have been informed by a person who passed it, any reefs at

all.CEYLON: a space about eighty miles in length of the southwestern and southern shores of these

islands has been described by Mr. Twynam ("Naut. Mag." 1836, pages 365 and 518); parts of this space

appear to be very regularly fringed by coralreefs, which extend from a quarter to half a mile from the shore.

These reefs are in places breached, and afford safe anchorage for the small trading craft. Outside, the sea

gradually deepens; there is forty fathoms about six miles off shore: this part I have coloured red. In the

published charts of Ceylon there appear to be fringingreefs in several parts of the southeastern shores,

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 92

which I have also coloured red.At Venloos Bay the shore is likewise fringed. North of Trincomalee there

are also reefs of the same kind. The sea off the northern part of Ceylon is exceedingly shallow; and therefore

I have not coloured the reefs which fringe portions of its shores, and the adjoining islets, as well as the Indian

These three great groups which have already been often noticed, are now wellknown from the admirable

surveys of Captain Moresby and Lieutenant Powell. The published charts, which are worthy of the most

attentive examination, at once show that the CHAGOS and MALDIVA groups are entirely formed of great

atolls, or lagoonformed reefs, surmounted by islets. In the LACCADIVE group, this structure is less

evident; the islets are low, not exceeding the usual height of coralformations (see Lieutenant Wood's

account, "Geographical Journal", volume vi., page 29), and most of the reefs are circular, as may be seen in

the published charts; and within several of them, as I am informed by Captain Moresby, there is deepish

water; these, therefore, have been coloured blue. Directly north, and almost forming part of this group, there

is a long, narrow, slightly curved bank, rising out of the depths of the ocean, composed of sand, shells, and

decayed coral, with from twentythree to thirty fathoms on it. I have no doubt that it has had the same origin

with the other Laccadive banks; but as it does not deepen towards the centre I have not coloured it. I might

have referred to other authorities regarding these three archipelagoes; but after the publication of the charts

by Captain Moresby, to whose personal kindness in giving me much information I am exceedingly indebted,

SAHIA DE MALHA bank consists of a series of narrow banks, with from eight to sixteen fathoms on them;

they are arranged in a semicircular manner, round a space about forty fathoms deep, which slopes on the S.E.

quarter to unfathomable depths; they are steepto on both sides, but more especially on the oceanside.

Hence this bank closely resembles in structure, and I may add from Captain Moresby's information in

composition, the Pitt's Bank in the Chagos group; and the Pitt's Bank, must, after what has been shown of the

Great Chagos Bank, be considered as a sunken, halfdestroyed atoll; hence coloured blue.CARGADOS

CARAJOS BANK. Its southern portion consists of a large, curved, coralshoal, with some low islets on its

eastern edge, and likewise some on the western side, between which there is a depth of about twelve fathoms.

Northward, a great bank extends. I cannot (probably owing to the want of perfect charts) refer this reef and

bank to any class;therefore not coloured.ILE DE SABLE is a little island, lying west of C. Carajos, only

some toises in height ("Voyage of the 'Favourite'," volume i., page 130); it is surrounded by reefs; but its

structure is unintelligible to me. There are some small banks north of it, of which I can find no clear

account.MAURITIUS. The reefs round this island have been described in the chapter on fringingreefs;

coloured red. RODRIGUEZ. The coralreefs here are exceedingly extensive; in one part they project even

five miles from the shore. As far as I can make out, there is no deepwater moat within them; and the sea

outside does not deepen very suddenly. The outline, however, of the land appears to be ("Life of Sir J.

Makintosh," volume ii., page 165) hilly and rugged. I am unable to decide whether these reefs belong to the

barrier class; as seems probable from their great extension, or to the fringing class; uncoloured.

BOURBON. The greater part of the shores of this island are without reefs; but Captain Carmichael

(Hooker's "Bot. Misc.") states that a portion, fifteen miles in length, on the S.E. side, is imperfectly fringed

The rocky islands of primary formation, composing this group, rise from a very extensive and tolerably level

bank, having a depth between twenty and forty fathoms. In Captain Owen's chart, and in that in the "Atlas of

the Voyage of the 'Favourite'," it appears that the east side of MAHE and the adjoining islands of ST. ANNE

and CERF, are regularly fringed by coralreefs. A portion of the S.E. part of CURIEUSE Island, the N., and

part of the S.W. shore of PRASLIN Island, and the whole west side of DIGUE Island, appear fringed. From a

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 93

MS. account of these islands by Captain F. Moresby, in the Admiralty, it appears that SILHOUETTE is also

fringed; he states that all these islands are formed of granite and quartz, that they rise abruptly from the sea,

and that "coralreefs have grown round them, and project for some distance." Dr. Allan, of Forres, who

visited these islands, informs me that there is no deep water between the reefs and the shore. The above

specified points have been coloured red. AMIRANTES Islands: The small islands of this neighbouring group,

according to the MS. account of them by Captain F. Moresby, are situated on an extensive bank; they consist

of the debris of corals and shells; are only about twenty feet in height, and are environed by reefs, some

attached to the shore, and some rather distant from it.I have taken great pains to procure plans and

information regarding the several islands lying between S.E. and S.W. of the Amirantes, and the Seychelles;

relying chiefly on Captain F. Moresby and Dr. Allan, it appears that the greater number, namelyPLATTE,

GLORIOSO, are low, formed of sand or coralrock, and irregularly shaped; they are situated on very

extensive banks, and are connected with great coralreefs. Galega is said by Dr. Allan, to be rather higher

than the other islands; and St. Pierre is described by Captain F. Moresby, as being cavernous throughout, and

as not consisting of either limestone or granite. These islands, as well as the Amirantes, certainly are not

atollformed, and they differ as a group from every other group with which I am acquainted; I have not

coloured them; but probably the reefs belong to the fringing class. Their formation is attributed, both by Dr.

Allan and Captain F. Moresby, to the action of the currents, here exceedingly violent, on banks, which no

doubt have had an independent geological origin. They resemble in many respects some islands and banks in

the West Indies, which owe their origin to a similar agency, in conjunction with an elevation of the entire

area. In close vicinity to the several islands, there are three others of an apparently different nature: first,

JUAN DE NOVA, which appears from some plans and accounts to be an atoll; but from others does not

appear to be so; not coloured. Secondly COSMOLEDO; "this group consists of a ring of coral, ten leagues in

circumference, and a quarter of a mile broad in some places, enclosing a magnificent lagoon, into which there

did not appear a single opening" (Horsburgh, volume i., page 151); coloured blue. Thirdly, ALDABRA; it

consists of three islets, about twentyfive feet in height, with red cliffs (Horsburgh, volume i., page 176)

surrounding a very shallow basin or lagoon. The sea is profoundly deep close to the shore. Viewing this

island in a chart, it would be thought an atoll; but the foregoing description shows that there is something

different in its nature; Dr. Allan also states that it is cavernous, and that the coralrock has a vitrified

MAYOTTA, according to Horsburgh (volume i., page 216, 4th edition), is completely surrounded by a reef,

which runs at the distance of three, four, and in some places even five miles from the land; in an old chart,

published by Dalrymple, a depth in many places of thirtysix and thirtyeight fathoms is laid down within

the reef. In the same chart, the space of open water within the reef in some parts is even more than three miles

wide: the land is bold and peaked; this island, therefore, is encircled by a wellcharacterised barrierreef, and

is coloured pale blue.JOHANNA; Horsburgh says (volume I. page 217) this island from the N.W. to the

S.W. point, is bounded by a reef, at the distance of two miles from the shore; in some parts, however, the reef

must be attached, since Lieutenant Boteler ("Narr." volume i., page 161) describes a passage through it,

within which there is room only for a few boats. Its height, as I am informed by Dr. Allan, is about 3,500 feet;

it is very precipitous, and is composed of granite, greenstone, and quartz; coloured blue.MOHILLA; on the

S. side of this island there is anchorage, in from thirty to fortyfive fathoms, between a reef and the shore

(Horsburgh, volume i., page 214); in Captain Owen's chart of Madagascar, this island is represented as

encircled; coloured blue.GREAT COMORO Island is, as I am informed by Dr. Allan, about 8,000 feet

high, and apparently volcanic; it is not regularly encircled; but reefs of various shapes and dimensions, jut out

from every headland on the W., S., and S.E. coasts, inside of which reefs there are channels, often parallel

with the shore, with deep water. On the northwestern coasts the reefs appear attached to the shores. The land

near the coast is in some places bold, but generally speaking it is flat; Horsburgh says (volume i., page 214)

the water is profoundly deep close to the SHORE, from which expression I presume some parts are without

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 94

reefs. From this description I apprehend the reef belongs to the barrier class; but I have not coloured it, as

most of the charts which I have seen, represent the reefs round it as very much less extensive than round the

My information is chiefly derived from the published charts by Captain Owen, and the accounts given by him

and by Lieutenant Boteler. Commencing at the S.W. extremity of the island; towards the northern part of the

STAR BANK (in latitude 25 deg S.) the coast for ten miles is fringed by a reef; coloured red. The shore

immediately S. of ST. AUGUSTINE'S BAY appears fringed; but TULLEAR Harbour, directly N. of it, is

formed by a narrow reef ten miles long, extending parallel to the shore, with from four to ten fathoms within

it. If this reef had been more extensive, it must have been classed as a barrierreef; but as the line of coast

falls inwards here, a submarine bank perhaps extends parallel to the shore, which has offered a foundation for

the growth of the coral; I have left this part uncoloured. From latitude 22 deg 16' to 21 deg 37', the shore is

fringed by coralreefs (see Lieutenant Boteler's "Narrative," volume ii., page 106), less than a mile in width,

and with shallow water within. There are outlying coralshoals in several parts of the offing, with about ten

fathoms between them and the shore, and the depth of the sea one mile and a half seaward, is about thirty

fathoms. The part above specified is engraved on a large scale; and as in the charts on rather a smaller scale

the same fringe of reef extends as far as latitude 33 deg 15'; I have coloured the whole of this part of the coast

red. The islands of JUAN DE NOVA (in latitude 17 deg S.) appear in the charts on a large scale to be fringed,

but I have not been able to ascertain whether the reefs are of coral; uncoloured. The main part of the west

coast appears to be low, with outlying sandbanks, which, Lieutenant Boteler (volume ii., page 106) says, "are

faced on the edge of deep water by a line of sharppointed coralrocks." Nevertheless I have not coloured

this part, as I cannot make out by the charts that the coast itself is fringed. The headlands of NARRENDA

and PASSANDAVA Bays (14 deg 40') and the islands in front of RADAMA HARBOUR are represented in

the plans as regularly fringed, and have accordingly been coloured red. With respect to the EAST COAST OF

MADAGASCAR, Dr. Allan informs me in a letter, that the whole line of coast, from TAMATAVE, in 18

deg 12', to C. AMBER, at the extreme northern point of the island, is bordered by coralreefs. The land is

low, uneven, and gradually rising from the coast. From Captain Owen's charts, also, the existence of these

reefs, which evidently belong to the fringing class, on some parts, namely N. of BRITISH SOUND, and near

NGONCY, of the above line of coast might have been inferred. Lieutenant Boteler (volume i., page 155)

speaks of "the reef surrounding the island of ST. MARY'S at a small distance from the shore." In a previous

chapter I have described, from the information of Dr. Allan, the manner in which the reefs extend in N.E.

lines from the headlands on this coast, thus sometimes forming rather deep channels within them, this seems

caused by the action of the currents, and the reefs spring up from the submarine prolongations of the sandy

headlands. The above specified portion of the coast is coloured red. The remaining S.E. portions do not

appear in any published chart to possess reefs of any kind; and the Rev. W. Ellis, whose means of

information regarding this side of Madagascar have been extensive, informs me he believes there are none.

Proceeding from the northern part, the coast appears, for a considerable space, without reefs. My information,

I may here observe, is derived from the survey by Captain Owen, together with his narrative; and that by

Lieutenant Boteler. At MUKDEESHA (10 deg 1' N.) there is a coralreef extending four or five miles along

the shore (Owen's "Narr." volume i, page 357) which in the chart lies at the distance of a quarter of a mile

from the shore, and has within it from six to ten feet water: this then is a fringingreef, and is coloured red.

From JUBA, a little S. of the equator, to LAMOO (in 2 deg 20' S.) "the coast and islands are formed of

madrepore" (Owen's "Narrative," volume i., page 363). The chart of this part (entitled DUNDAS Islands),

presents an extraordinary appearance; the coast of the mainland is quite straight and it is fronted at the

average distance of two miles, by exceedingly narrow, straight islets, fringed with reefs. Within the chain of

islets, there are extensive tidal flats and muddy bays, into which many rivers enter; the depths of these spaces

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 95

varies from one to four fathomsthe latter depth not being common, and about twelve feet the average.

Outside the chain of islets, the sea, at the distance of a mile, varies in depth from eight to fifteen fathoms.

Lieutenant Boteler ("Narr." volume i., page 369) describes the muddy bay of PATTA, which seems to

resemble other parts of this coast, as fronted by small, narrow, level islets formed of decomposing coral, the

margin of which is seldom of greater height than twelve feet, overhanging the rocky surface from which the

islets rise. Knowing that the islets are formed of coral, it is, I think, scarcely possible to view the coast, and

not at once conclude that we here see a fringingreef, which has been upraised a few feet: the unusual depth

of from two to four fathoms within some of these islets, is probably due to muddy rivers having prevented the

growth of coral near the shore. There is, however, one difficulty on this view, namely, that before the

elevation took place, which converted the reef into a chain of islets, the water must apparently have been still

deeper; on the other hand it may be supposed that the formation of a nearly perfect barrier in front, of so large

an extent of coast, would cause the currents (especially in front of the rivers), to deepen their muddy beds.

When describing in the chapter on fringingreefs, those of Mauritius, I have given my reasons for believing

that the shoal spaces within reefs of this kind, must, in many instances, have been deepened. However this

may be, as several parts of this line of coast are undoubtedly fringed by living reefs, I have coloured it red.

MALEENDA (3 deg 20' S.). In the plan of the harbour, the south headland appears fringed; and in Owen's

chart on a larger scale, the reefs are seen to extend nearly thirty miles southward; coloured red.MOMBAS

(4 deg 5' S.). The island which forms the harbour, "is surrounded by cliffs of madrepore, capable of being

rendered almost impregnable" (Owen's "Narr." volume i., page 412). The shore of the mainland N. and S. of

the harbour, is most regularly fringed by a coralreef at a distance from half a mile to one mile and a quarter

from the land; within the reef the depth is from nine to fifteen feet; outside the reef the depth at rather less

than half a mile is thirty fathoms. From the charts it appears that a space about thirtysix miles in length, is

here fringed; coloured red.PEMBA (5 deg S.) is an island of coralformation, level, and about two

hundred feet in height (Owen's "Narr." volume i., page 425); it is thirtyfive miles long, and is separated

from the mainland by a deep sea. The outer coast is represented in the chart as regularly fringed; coloured

red. The mainland in front of Pemba is likewise fringed; but there also appear to be some outlying reefs with

deep water between them and the shore. I do not understand their structure, either from the charts or the

description, therefore have not coloured them.ZANZIBAR resembles Pemba in most respects; its southern

half on the western side and the neighbouring islets are fringed; coloured red. On the mainland, a little S. of

Zanzibar, there are some banks parallel to the coast, which I should have thought had been formed of coral,

had it not been said (Boteler's "Narr." volume ii., page 39) that they were composed of sand; not

coloured.LATHAM'S BANK is a small island, fringed by coralreefs; but being only ten feet high, it has

not been coloured.MONFEEA is an island of the same character as Pemba; its outer shore is fringed, and

its southern extremity is connected with Keelwa Point on the mainland by a chain of islands fringed by reefs;

coloured red. The four lastmentioned islands resemble in many respects some of the islands in the Red Sea,

which will presently be described. KEELWA. In a plan of the shore, a space of twenty miles N. and S. of

this place is fringed by reefs, apparently of coral: these reefs are prolonged still further southward in Owen's

general chart. The coast in the plans of the rivers LINDY and MONGHOW (9 deg 59' and 10 deg 7' S.) has

the same structure; coloured red.QUERIMBA Islands (from 10 deg 40' to 13 deg S.). A chart on a large

scale is given of these islands; they are low, and of coralformation (Boteler's "Narr." volume ii., page 54);

and generally have extensive reefs projecting from them which are dry at low water, and which on the outside

rise abruptly from a deep sea: on their insides they are separated from the continent by a channel, or rather a

succession of bays, with an average depth of ten fathoms. The small headlands on the continent also have

coralbanks attached to them; and the Querimba islands and banks are placed on the lines of prolongation of

these headlands, and are separated from them by very shallow channels. It is evident that whatever cause,

whether the drifting of sediment or subterranean movements, produced the headlands, likewise produced, as

might have been expected, submarine prolongations to them; and these towards their outer extremities, have

since afforded a favourable basis for the growth of coralreefs, and subsequently for the formation of islets.

As these reefs clearly belong to the fringing class, the Querimba islands have been coloured

red.MONABILA (13 deg 32' S.). In the plan of this harbour, the headlands outside are fringed by reefs

apparently of coral; coloured red.MOZAMBIQUE (150 deg S.) The outer part of the island on which the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 96

city is built, and the neighbouring islands, are fringed by coralreefs; coloured red. From the description

given in Owen's "Narr." (volume i., page 162), the shore from MOZAMBIQUE to DELAGOA BAY appears

to be low and sandy; many of the shoals and islets off this line of coast are of coralformation; but from their

small size and lowness, it is not possible, from the charts, to know whether they are truly fringed. Hence this

portion of coast is left uncoloured, as are likewise those parts more northward, of which no mention has been

From the charts lately published on a large scale by the East India Company, it appears that several parts,

especially the southern shores of this gulf, are fringed by coralreefs; but as the water is very shallow, and as

there are numerous sandbanks, which are difficult to distinguish on the chart from reefs, I have not coloured

the upper part red. Towards the mouth, however, where the water is rather deeper, the islands of ORMUZ and

LARRACK, appear so regularly fringed, that I have coloured them red. There are certainly no atolls in the

Persian Gulf. The shores of IMMAUM, and of the promontory forming the southern headland of the Persian

Gulf, seem to be without reefs. The whole S.W. part (except one or two small patches) of ARABIA FELIX,

and the shores of SOCOTRA appear from the charts and memoir of Captain Haines ("Geographical Journal,"

1839, page 125) to be without any reefs. I believe there are no extensive coralreefs on any part of the coasts

of INDIA, except on the low promontory of MADURA (as already mentioned) in front of Ceylon.

My information is chiefly derived from the admirable charts published by the East India Company in 1836,

from personal communication with Captain Moresby, one of the surveyors, and from the excellent memoir,

"Uber die Natur der CorallenBanken des Rothen Meeres," by Ehrenberg. The plains immediately bordering

the Red Sea seem chiefly to consist of a sedimentary formation of the newer tertiary period. The shore is,

with the exception of a few parts, fringed by coralreefs. The water is generally profoundly deep close to the

shore; but this fact, which has attracted the attention of most voyagers, seems to have no necessary

connection with the presence of reefs; for Captain Moresby particularly observed to me, that, in latitude 24

deg 10' on the eastern side, there is a piece of coast, with very deep water close to it, without any reefs, but

not differing in other respects from the usual nature of the coastline. The most remarkable feature in the Red

Sea is the chain of submerged banks, reefs, and islands, lying some way from the shore, chiefly on the eastern

side; the space within being deep enough to admit a safe navigation in small vessels. The banks are generally

of an oval form, and some miles in width; but some of them are very long in proportion to their width.

Captain Moresby informs me that any one, who had not made actual plans of them, would be apt to think that

they were much more elongated than they really are. Many of them rise to the surface, but the greater number

lie from five to thirty fathoms beneath it, with irregular soundings on them. They consist of sand and living

coral; coral on most of them, according to Captain Moresby, covering the greater part of their surface. They

extend parallel to the shore, and they are not unfrequently connected in their middle parts by short transverse

banks with the mainland. The sea is generally profoundly deep quite close to them, as it is near most parts of

the coast of the mainland; but this is not universally the case, for between latitude 15 deg and 17 deg the

water deepens quite gradually from the banks, both on the eastern and western shores, towards the middle of

the sea. Islands in many parts arise from these banks; they are low, flattopped, and consist of the same

horizontally stratified formation with that forming the plainlike margin of the mainland. Some of the smaller

and lower islands consist of mere sand. Captain Moresby informs me, that small masses of rock, the remnants

of islands, are left on many banks where there is now no dry land. Ehrenberg also asserts that most of the

islets, even the lowest, have a flat abraded basis, composed of the same tertiary formation: he believes that as

soon as the surf wears down the protuberant parts of a bank, just beneath the level of the sea, the surface

becomes protected from further abrasion by the growth of coral, and he thus accounts for the existence of so

many banks standing on a level with the surface of this sea. It appears that most of the islands are certainly

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 97

The form of the banks and islands is most singular in the part just referred to, namely, from latitude 15 deg to

17 deg, where the sea deepens quite gradually: the DHALAC group, on the western coast, is surrounded by

an intricate archipelago of islets and shoals; the main island is very irregularly shaped, and it includes a bay

seven miles long, by four across, in which no bottom was found with 252 feet: there is only one entrance into

this bay, half a mile wide, and with an island in front of it. The submerged banks on the eastern coast, within

the same latitudes, round FARSAN Island, are, likewise, penetrated by many narrow creeks of deep water;

one is twelve miles long, in the form of a hatchet, in which, close to its broad upper end, soundings were not

struck with 360 feet, and its entrance is only half a mile wide: in another creek of the same nature, but even

with a more irregular outline, there was no bottom with 480 feet. The island of Farsan, itself, has as singular a

form as any of its surrounding banks. The bottom of the sea round the Dhalac and Farsan Islands consists

chiefly of sand and agglutinated fragments, but, in the deep and narrow creeks, it consists of mud; the islands

themselves consist of thin, horizontally stratified, modern tertiary beds, containing but little broken coral

(Ruppell, "Reise in Abyssinie," Band. i., S. 247.), their shores are fringed by living coralreefs.

From the account given by Ruppell (Ibid., S. 245.) of the manner in which Dhalac has been rent by fissures,

the opposite sides of which have been unequally elevated (in one instance to the amount of fifty feet), it

seems probable that its irregular form, as well as probably that of Farsan, may have been partly caused by

unequal elevations; but, considering the general form of the banks, and of the deepwater creeks, together

with the composition of the land, I think their configuration is more probably due in great part to strong

currents having drifted sediment over an uneven bottom: it is almost certain that their form cannot be

attributed to the growth of coral. Whatever may have been the precise origin of the Dhalac and Farsan

Archipelagoes, the greater number of the banks on the eastern side of the Red Sea seem to have originated

through nearly similar means. I judge of this from their similarity in configuration (in proof of which I may

instance a bank on the east coast in latitude 22 deg; and although it is true that the northern banks generally

have a less complicated outline), and from their similarity in composition, as may be observed in their

upraised portions. The depth within the banks northward of latitude 17 deg, is usually greater, and their outer

sides shelve more abruptly (circumstances which seem to go together) than in the Dhalac and Farsan

Archipelagoes; but this might easily have been caused by a difference in the action of the currents during

their formation: moreover, the greater quantity of living coral, which, according to Captain Moresby, exists

From this account, brief and imperfect as it is, we can see that the great chain of banks on the eastern coast,

and on the western side in the southern portion, differ greatly from true barrierreefs wholly formed by the

growth of coral. It is indeed the direct conclusion of Ehrenberg ("Uber die," etc., pages 45 and 51), that they

are connected in their origin quite secondarily with the growth of coral; and he remarks that the islands off

the coast of Norway, if worn down level with the sea, and merely coated with living coral, would present a

nearly similar appearance. I cannot, however, avoid suspecting, from information given me by Dr.

Malcolmson and Captain Moresby, that Ehrenberg has rather underrated the influence of corals, in some

There are, in this space, reefs, which, if I had known nothing of those in other parts of the Red Sea, I should

unhesitatingly have considered as barrierreefs; and, after deliberation, I have come to the same conclusion.

One of these reefs, in 20 deg 15', is twenty miles long, less than a mile in width (but expanding at the

northern end into a disc), slightly sinuous, and extending parallel to the mainland at the distance of five miles

from it, with very deep water within; in one spot soundings were not obtained with 205 fathoms. Some

leagues further south, there is another linear reef, very narrow, ten miles long, with other small portions of

reef, north and south, almost connected with it; and within this line of reefs (as well as outside) the water is

profoundly deep. There are also some small linear and sickleformed reefs, lying a little way out at sea. All

these reefs are covered, as I am informed by Captain Moresby, by living corals. Here, then, we have all the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 98

characters of reefs of the barrier class; and in some outlying reefs we have an approach to the structure of

atolls. The source of my doubts about the classification of these reefs, arises from having observed in the

Dhalac and Farsan groups the narrowness and straightness of several spits of sand and rock: one of these spits

in the Dhalac group is nearly fifteen miles long, only two broad, and it is bordered on each side with deep

water; so that, if worn down by the surf, and coated with living corals, it would form a reef nearly similar to

those within the space under consideration. There is, also, in this space (latitude 21 deg) a peninsula, bordered

by cliffs, with its extremity worn down to the level of the sea, and its basis fringed with reefs: in the line of

prolongation of this peninsula, there lies the island of MACOWA (formed, according to Captain Moresby, of

the usual tertiary deposit), and some smaller islands, large parts of which likewise appear to have been worn

down, and are now coated with living corals. If the removal of the strata in these several cases had been more

complete, the reefs thus formed would have nearly resembled those barrierlike ones now under discussion.

Notwithstanding these facts, I cannot persuade myself that the many very small, isolated, and sickleformed

reefs and others, long, nearly straight, and very narrow, with the water unfathomably deep close round them,

could possibly have been formed by corals merely coating banks of sediment, or the abraded surfaces of

irregularly shaped islands. I feel compelled to believe that the foundations of these reefs have subsided, and

that the corals, during their upward growth, have given to these reefs their present forms: I may remark that

the subsidence of narrow and irregularlyshaped peninsulas and islands, such as those existing on the coasts

of the Red Sea, would afford the requisite foundations for the reefs in question.

This part of the coast (north of the space coloured blue on the map) is fronted by an irregularly shelving bank,

from about ten to thirty fathoms deep; numerous little reefs, some of which have the most singular shapes,

rise from this bank. It may be observed, respecting one of them, in latitude 23 deg 10', that if the promontory

in latitude 24 deg were worn down to the level of the sea, and coated with corals, a very similar and

grotesquely formed reef would be produced. Many of the reefs on this part of the coast may thus have

originated; but there are some sickle, and almost atollformed reefs lying in deep water off the promontory in

latitude 24 deg, which lead me to suppose that all these reefs are more probably allied to the barrier or atoll

classes. I have not, however, ventured to colour this portion of coast. ON THE WEST COAST FROM

LATITUDE 19 DEG TO 17 DEG (south of space coloured blue on the map), there are many low islets of

very small dimensions, not much elongated, and rising out of great depths at a distance from the coast; these

cannot be classed either with atolls, or barrier or fringingreefs. I may here remark that the outlying reefs on

the west coast, between latitude 19 deg and 24 deg, are the only ones in the Red Sea, which approach in

structure to the true atolls of the Indian and Pacific Oceans, but they present only imperfect miniature

I have felt the greatest doubt about colouring any portion of this coast, north of the fringingreefs round the

Farsan Islands in 16 deg 10'. There are many small outlying coralreefs along the whole line of coast; but as

the greater number rise from banks not very deeply submerged (the formation of which has been shown to be

only secondarily connected with the growth of coral), their origin may be due simply to the growth of knolls

of corals, from an irregular foundation situated within a limited depth. But between latitude 18 deg and 20

deg, there are so many linear, elliptic, and extremely small reefs, rising abruptly out of profound depths, that

the same reasons, which led me to colour blue a portion of the west coast, have induced me to do the same in

this part. There exist some small outlying reefs rising from deep water, north of latitude 20 deg (the northern

limit coloured blue), on the east coast; but as they are not very numerous and scarcely any of them linear, I

In the SOUTHERN PARTS of the Red Sea, considerable spaces of the mainland, and of some of the Dhalac

islands, are skirted by reefs, which, as I am informed by Captain Moresby, are of living coral, and have all the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 99

characters of the fringing class. As in these latitudes, there are no outlying linear or sickleformed reefs,

rising out of unfathomable depths, I have coloured these parts of the coast red. On similar grounds, I have

coloured red the NORTHERN PARTS OF THE WESTERN COAST (north of latitude 24 deg 30'), and

likewise the shores of the chief part of the GULF OF SUEZ. In the GULF OF ACABA, as I am informed by

My information regarding the reefs of this area, is derived from various sources, and from an examination of

numerous charts; especially of those lately executed during the survey under Captain Owen, R.N. I lay under

particular obligation to Captain Bird Allen, R.N., one of the members of the late survey, for many personal

communications on this subject. As in the case of the Red Sea, it is necessary to make some preliminary

remarks on the submerged banks of the West Indies, which are in some degree connected with coralreefs,

and cause considerable doubts in their classification. That large accumulations of sediment are in progress on

the West Indian shores, will be evident to any one who examines the charts of that sea, especially of the

portion north of a line joining Yucutan and Florida. The area of deposition seems less intimately connected

with the debouchement of the great rivers, than with the course of the seacurrents; as is evident from the

Besides the coastbanks, there are many of various dimensions which stand quite isolated; these closely

resemble each other, they lie from two or three to twenty or thirty fathoms under water, and are composed of

sand, sometimes firmly agglutinated, with little or no coral; their surfaces are smooth and nearly level,

shelving only to the amount of a few fathoms, very gradually all round towards their edges, where they

plunge abruptly into the unfathomable sea. This steep inclination of their sides, which is likewise

characteristic of the coastbanks, is very remarkable: I may give as an instance, the Misteriosa Bank, on the

edges of which the soundings change in 250 fathoms horizontal distance, from 11 to 210 fathoms; off the

northern point of the bank of Old Providence, in 200 fathoms horizontal distance, the change is from 19 to

152 fathoms; off the Great Bahama Bank, in 160 fathoms horizontal distance, the inclination is in many

places from 10 fathoms to no bottom with 190 fathoms. On coasts in all parts of the world, where sediment is

accumulating, something of this kind may be observed; the banks shelve very gently far out to sea, and then

terminate abruptly. The form and composition of the banks standing in the middle parts of the W. Indian Sea,

clearly show that their origin must be chiefly attributed to the accumulation of sediment; and the only

obvious explanation of their isolated position is the presence of a nucleus, round which the currents have

collected fine drift matter. Any one who will compare the character of the bank surrounding the hilly island

of Old Providence, with those banks in its neighbourhood which stand isolated, will scarcely doubt that they

surround submerged mountains. We are led to the same conclusion by examining the bank called Thunder

Knoll, which is separated from the Great Mosquito Bank by a channel only seven miles wide, and 145

fathoms deep. There cannot be any doubt that the Mosquito Bank has been formed by the accumulation of

sediment round the promontory of the same name; and Thunder Knoll resembles the Mosquito Bank, in the

state of its surface submerged twenty fathoms, in the inclinations of its sides, in composition, and in every

other respect. I may observe, although the remark is here irrelevant, that geologists should be cautious in

concluding that all the outlyers of any formation have once been connected together, for we here see that

deposits, doubtless of exactly the same nature, may be deposited with large valleylike spaces between them.

Linear strips of coralreefs and small knolls project from many of the isolated, as well as coastbanks;

sometimes they occur quite irregularly placed, as on the Mosquito Bank, but more generally they form

crescents on the windward side, situated some little distance within the outer edge of the banks:thus on the

Serranilla Bank they form an interrupted chain which ranges between two and three miles within the

windward margin: generally they occur, as on Roncador, Courtown, and Anegada Banks, nearer the line of

deep water. Their occurrence on the windward side is conformable to the general rule, of the efficient kinds

of corals flourishing best where most exposed; but their position some way within the line of deep water I

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 100

cannot explain, without it be, that a depth somewhat less than that close to the outer margin of the banks, is

most favourable to their growth. Where the corals have formed a nearly continuous rim, close to the

windward edge of a bank some fathoms submerged, the reef closely resembles an atoll; but if the bank

surrounds an island (as in the case of Old Providence), the reef resembles an encircling barrierreef. I should

undoubtedly have classed some of these fringed banks as imperfect atolls, or barrierreefs, if the sedimentary

nature of their foundations had not been evident from the presence of other neighbouring banks, of similar

forms and of similar composition, but without the crescentlike marginal reef: in the third chapter, I observed

that probably some atolllike reefs did exist, which had originated in the manner here supposed.

Proofs of elevation within recent tertiary periods abound, as referred to in the sixth chapter, over nearly the

whole area of the West Indies. Hence it is easy to understand the origin of the low land on the coasts, where

sediment is now accumulating; for instance on the northern part of Yucutan, and on the N.E. part of

Mosquito, where the land is low, and where extensive banks appear to be in progressive formation. Hence,

also, the origin of the Great Bahama Banks, which are bordered on their western and southern edges by very

narrow, long, singularly shaped islands, formed of sand, shells, and coralrock, and some of them about a

hundred feet in height, is easily explained by the elevation of banks fringed on their windward (western and

southern) sides by coralreefs. On this view, however, we must suppose either that the chief part of the

surfaces of the great Bahama sandbanks were all originally deeply submerged, and were brought up to their

present level by the same elevatory action, which formed the linear islands; or that during the elevation of the

banks, the superficial currents and swell of the waves continued wearing them down and keeping them at a

nearly uniform level: the level is not quite uniform; for, in proceeding from the N.W. end of the Bahama

group towards the S.E. end, the depth of the banks increases, and the area of land decreases, in a very gradual

and remarkable manner. The latter view, namely, that these banks have been worn down by the currents and

swell during their elevation, seems to me the most probable one. It is, also, I believe, applicable to many

banks, situated in widely distant parts of the West Indian Sea, which are wholly submerged; for, on any other

view, we must suppose, that the elevatory forces have acted with astonishing uniformity.

The shores of the Gulf of Mexico, for the space of many hundred miles, is formed by a chain of lagoons,

from one to twenty miles in breadth ("Columbian Navigator," page 178, etc.), containing either fresh or salt

water, and separated from the sea by linear strips of sand. Great spaces of the shores of Southern Brazil (In

the "London and Edinburgh Philosophical Journal," 1841, page 257, I have described a singular bar of

sandstone lying parallel to the coast off Pernambuco in Brazil, which probably is an analogous formation.),

and of the United States from Long Island (as observed by Professor Rogers) to Florida have the same

character. Professor Rogers, in his "Report to the British Association" (volume iii., page 13), speculates on

the origin of these low, sandy, linear islets; he states that the layers of which they are composed are too

homogeneous, and contain too large a proportion of shells, to permit the common supposition of their

formation being simply due to matter thrown up, where it now lies, by the surf: he considers these islands as

upheaved bars or shoals, which were deposited in lines where opposed currents met. It is evident that these

islands and spits of sand parallel to the coast, and separated from it by shallow lagoons, have no necessary

connection with coralformations. But in Southern Florida, from the accounts I have received from persons

who have resided there, the upraised islands seem to be formed of strata, containing a good deal of coral, and

they are extensively fringed by living reefs; the channels within these islands are in some places between two

and three miles wide, and five or six fathoms deep, though generally (In the ordinary seacharts, no lagoons

appear on the coast of Florida, north of 26 deg; but Major Whiting ("Silliman's Journal," volume xxxv., page

54) says that many are formed by sand thrown up along the whole line of coast from St. Augustine's to

Jupiter Inlet.) they are less in depth than width. After having seen how frequently banks of sediment in the

West Indian Sea are fringed by reefs, we can readily conceive that bars of sediment might be greatly aided in

their formation along a line of coast, by the growth of corals; and such bars would, in that case, have a

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 101

Having now endeavoured to remove some sources of doubt in classifying the reefs of the West Indies, I will

give my authorities for colouring such portions of the coast as I have thought myself warranted in doing.

Captain Bird Allen informs me, that most of the islands on the BAHAMA BANKS are fringed, especially on

their windward sides, with living reefs; and hence I have coloured those, which are thus represented in

Captain Owen's late chart, red. The same officer informs me, that the islands along the southern part of

FLORIDA are similarly fringed; coloured red. CUBA: Proceeding along the northern coast, at the distance of

forty miles from the extreme S.E. point, the shores are fringed by reefs, which extend westward for a space of

160 miles, with only a few breaks. Parts of these reefs are represented in the plans of the harbours on this

coast by Captain Owen; and an excellent description is given of them by Mr. Taylor (Loudon's "Mag. of Nat.

Hist." volume ix., page 449); he states that they enclosed a space called the "baxo," from half to

threequarters of a mile in width, with a sandy bottom, and a little coral. In most parts people can wade, at

low water, to the reef; but in some parts the depth is between two and three fathoms. Close outside the reef,

the depth is between six and seven fathoms; these wellcharacterised fringingreefs are coloured red.

Westward of longitude 77 deg 30', on the northern side of Cuba, a great bank commences, which extends

along the coast for nearly four degrees of longitude. In the place of its commencement, in its structure, and in

the "CAYS," or low islands on its edge, there is a marked correspondence (as observed by Humboldt, "Pers.

Narr." volume vii., page 88) between it and the Great Bahama and Sal Banks, which lie directly in front.

Hence one is led to attribute the same origin to both these sets of banks; namely, the accumulation of

sediment, conjoined with an elevatory movement, and the growth of coral on their outward edges; those parts

which appear fringed by living reefs are coloured red. Westward of these banks, there is a portion of coast

apparently without reefs, except in the harbours, the shores of which seem in the published plans to be

fringed. The COLORADO SHOALS (see Captain Owen's charts), and the low land at the western end of

Cuba, correspond as closely in relative position and structure to the banks at the extreme point of Florida, as

the banks above described on the north side of Cuba, do to the Bahamas, the depth within the islets and reefs

on the outer edge of the COLORADOS, is generally between two and three fathoms, increasing to twelve

fathoms in the southern part, where the bank becomes nearly open, without islets or coralreefs; the portions

which are fringed are coloured red. The southern shore of Cuba is deeply concave, and the included space is

filled up with mud and sandbanks, low islands and coralreefs. Between the mountainous ISLE OF PINES

and the southern shore of Cuba, the general depth is only between two and three fathoms; and in this part

small islands, formed of fragmentary rock and broken madrepores (Humboldt, "Pers. Narr." volume vii.

pages 51, 86 to 90, 291, 309, 320), rise abruptly, and just reach the surface of the sea. From some expressions

used in the "Columbian Navigator" (volume i., part ii., page 94), it appears that considerable spaces along the

outer coast of Southern Cuba are bounded by cliffs of coralrock, formed probably by the upheaval of

coralreefs and sandbanks. The charts represent the southern part of the Isle of Pines as fringed by reefs,

which the "Columb. Navig." says extend some way from the coast, but have only from nine to twelve feet

water on them; these are coloured red.I have not been able to procure any detailed description of the large

groups of banks and "cays" further eastward on the southern side of Cuba; within them there is a large

expanse, with a muddy bottom, from eight to twelve fathoms deep; although some parts of this line of coast

are represented in the general charts of the West Indies, as fringed, I have not thought it prudent to colour

them. The remaining portion of the south coast of Cuba appears to be without coralreefs.

The N.E. part of the promontory appears in Captain Owen's charts to be fringed; coloured red. The eastern

coast, from 20 deg to 18 deg is fringed. South of latitude 18 deg, there commences the most remarkable reef

in the West Indies: it is about one hundred and thirty miles in length, ranging in a N. and S. line, at an

average distance of fifteen miles from the coast. The islets on it are all low, as I have been informed by

Captain B. Allen; the water deepens suddenly on the outside of the reef, but not more abruptly than off many

of the sedimentary banks: within its southern extremity (off HONDURAS) the depth is twentyfive fathoms;

but in the more northern parts, the depth soon increases to ten fathoms, and within the northernmost part, for

a space of twenty miles, the depth is only from one to two fathoms. In most of these respects we have the

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 102

characteristics of a barrierreef; nevertheless, from observing, first, that the channel within the reef is a

continuation of a great irregular bay, which penetrates the mainland to the depth of fifty miles; and secondly,

that considerable spaces of this barrierlike reef are described in the charts (for instance, in latitude 16 deg

45' and 16 deg 12') as formed of pure sand; and thirdly, from knowing that sediment is accumulating in many

parts of the West Indies in banks parallel to the shore; I have not ventured to colour this reef as a barrier,

without further evidence that it has really been formed by the growth of corals, and that it is not merely in

parts a spit of sand, and in other parts a worn down promontory, partially coated and fringed by reefs; I lean,

however, to the probability of its being a barrierreef, produced by subsidence. To add to my doubts,

immediately on the outside of this barrierlike reef, TURNEFFE, LIGHTHOUSE, and GLOVER reefs are

situated, and these reefs have so completely the form of atolls, that if they had occurred in the Pacific, I

should not have hesitated about colouring them blue. TURNEFFE REEF seems almost entirely filled up with

low mud islets; and the depth within the other two reefs is only from one to three fathoms. From this

circumstance and from their similarity in form, structure, and relative position, both to the bank called

NORTHERN TRIANGLES, on which there is an islet between seventy and eighty feet, and to COZUMEL

Island, the level surface of which is likewise between seventy and eighty feet in height, I consider it more

probable that the three foregoing banks are the worn down bases of upheaved shoals, fringed with corals, than

that they are true atolls, wholly produced by the growth of coral during subsidence; left uncoloured.

In front of the eastern MOSQUITO coast, there are between latitude 12 deg and 16 deg some extensive banks

(already mentioned, page 148), with high islands rising from their centres; and there are other banks wholly

submerged, both of which kinds of banks are bordered, near their windward margins, by crescentshaped

coralreefs. But it can hardly be doubted, as was observed in the preliminary remarks, that these banks owe

their origin, like the great bank extending from the Mosquito promontory, almost entirely to the accumulation

CAYMAN ISLAND: this island appears in the charts to be fringed; and Captain B. Allen informs me that the

reefs extend about a mile from the shore, and have only from five to twelve feet water within them; coloured

red.JAMAICA: judging from the charts, about fifteen miles of the S.E. extremity, and about twice that

length on the S.W. extremity, and some portions on the S. side near Kingston and Port Royal, are regularly

fringed, and therefore are coloured red. From the plans of some harbours on the N. side of Jamaica, parts of

the coast appear to be fringed; but as these are not represented in the charts of the whole island, I have not

coloured them.ST. DOMINGO: I have not been able to obtain sufficient information, either from plans of

the harbours, or from general charts, to enable me to colour any part of the coast, except sixty miles from Port

de Plata westward, which seems very regularly fringed; many other parts, however, of the coast are probably

fringed, especially towards the eastern end of the island.PUERTO RICO: considerable portions of the

southern, western, and eastern coasts, and some parts of the northern coast, appear in the charts to be fringed;

coloured red.Some miles in length of the southern side of the Island of ST. THOMAS is fringed; most of

the VIRGIN GORDA Islands, as I am informed by Mr. Schomburgk, are fringed; the shores of ANEGADA,

as well as the bank on which it stands, are likewise fringed; these islands have been coloured red. The greater

part of the southern side of SANTA CRUZ appears in the Danish survey to be fringed (see also Prof. Hovey's

account of this island, in "Silliman's Journal," volume xxxv., page 74); the reefs extend along the shore for a

considerable space, and project rather more than a mile; the depth within the reef is three fathoms; coloured

red.The ANTILLES, as remarked by Von Buch ("Descrip. Iles Canaries," page 494), may be divided into

two linear groups, the western row being volcanic, and the eastern of modern calcareous origin; my

information is very defective on the whole group. Of the eastern islands, BARBUDA and the western coasts

of ANTIGUA and MARIAGALANTE appear to be fringed: this is also the case with BARBADOES, as I

have been informed by a resident; these islands are coloured red. On the shores of the Western Antilles, of

volcanic origin, very few coralreefs appear to exist. The island of MARTINIQUE, of which there are

beautifully executed French charts, on a very large scale, alone presents any appearance worthy of special

notice. The southwestern, southern, and eastern coasts, together forming about half the circumference of the

island, are skirted by very irregular banks, projecting generally rather less than a mile from the shore, and

CHAPTER VI.ON THE DISTRIBUTION OF CORALREEFS WITH REFERENCE TO THE THEORY OF THEIR FORMATION. 103

lying from two to five fathoms submerged. In front of almost every valley, they are breached by narrow,

crooked, steepsided passages. The French engineers ascertained by boring, that these submerged banks

consisted of madreporitic rocks, which were covered in many parts by thin layers of mud or sand. From this

fact, and especially from the structure of the narrow breaches, I think there can be little doubt that these banks

once formed living reefs, which fringed the shores of the island, and like other reefs probably reached the

surface. From some of these submerged banks reefs of living coral rise abruptly, either in small detached

patches, or in lines parallel to, but some way within the outer edges of the banks on which they are based.

Besides the above banks which skirt the shores of the island, there is on the eastern side a range of linear

banks, similarly constituted, twenty miles in length, extending parallel to the coast line, and separated from it

by a space between two and four miles in width, and from five to fifteen fathoms in depth. From this range of

detached banks, some linear reefs of living coral likewise rise abruptly; and if they had been of greater length

(for they do not front more than a sixth part of the circumference of the island), they would necessarily from

their position have been coloured as barrierreefs; as the case stands they are left uncoloured. I suspect that

after a small amount of subsidence, the corals were killed by sand and mud being deposited on them, and the

reefs being thus prevented from growing upwards, the banks of madreporitic rock were left in their present

THE BERMUDA Islands have been carefully described by Lieutenant Nelson, in an excellent Memoir in the

"Geological Transactions" (volume v., part i., page 103). In the form of the bank or reef, on one side of which

the islands stand, there is a close general resemblance to an atoll; but in the following respects there is a

considerable difference,first, in the margin of the reef not forming (as I have been informed by Mr.

Chaffers, R.N.) a flat, solid surface, laid bare at low water, and regularly bounding the internal space of

shallow water or lagoon; secondly, in the border of gradually shoaling water, nearly a mile and a half in

width, which surrounds the entire outside of the reef (as is laid down in Captain Hurd's chart); and thirdly, in

the size, height, and extraordinary form of the islands, which present little resemblance to the long, narrow,

simple islets, seldom exceeding half a mile in breadth, which surmount the annular reefs of almost all the

atolls in the Indian and Pacific Oceans. Moreover, there are evident proofs (Nelson, Ibid., page 118), that

islands similar to the existing ones, formerly extended over other parts of the reef. It would, I believe, be

difficult to find a true atoll with land exceeding thirty feet in height; whereas, Mr. Nelson estimates the

highest point of the Bermuda Islands to be 260 feet; if, however, Mr. Nelson's view, that the whole of the

land consists of sand drifted by the winds, and agglutinated together, were proved correct, this difference

would be immaterial; but, from his own account (page 118), there occur in one place, five or six layers of red

earth, interstratified with the ordinary calcareous rock, and including stones too heavy for the wind to have

moved, without having at the same time utterly dispersed every grain of the accompanying drifted matter. Mr.

Nelson attributes the origin of these several layers, with their embedded stones, to as many violent

catastrophes; but further investigation in such cases has generally succeeded in explaining phenomena of this

kind by ordinary and simpler means. Finally, I may remark, that these islands have a considerable

resemblance in shape to Barbuda in the West Indies, and to Pemba on the eastern coast of Africa, which latter

island is about two hundred feet in height, and consists of coralrock. I believe that the Bermuda Islands,

from being fringed by living reefs, ought to have been coloured red; but I have left them uncoloured, on

account of their general resemblance in external form to a lagoonisland or atoll.

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