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of Mahlos Mahdoo (Plate II. fig. 4), it was not found easy to define the islets and the little lagoons within each reef, so that the ring-formed structure is very imperfectly shown: in the large published charts of Tilla-dou-Matte, the appearance of these rings, from standing further apart from each other, is very rema... |
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... |
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,* within which there is a flat surface of coral-rock; on this flat, sand and fragments have in ... |
been converted into islets, clothed with vegetation. I can, in fact, point out no essential difference between these little ring-formed reefs (which, however, are larger, and contain deeper lagoons than many true atolls that stand in the open sea), and the most perfectly characterized atolls, excepting that the ring-fo... |
floor of the open sea, and that instead of being scattered irregularly, they are grouped closely together on one large platform, with the marginal rings arranged in a rudely-formed circle. The perfect series which can be traced from portions of simple linear reef, to others including long linear lagoons, * Capt. Moresb... |
the commonest kinds on the outer margin, as it is at Keeling atoll. 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 ring-formed reefs on the margin, even where most perfect and s... |
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 ring-formed 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... |
ring-like 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 ring-fo... |
are somewhat broader, the marginal portions of reef, and especially those close to the larger channels, are ring-formed, but the central ones are not so; where they are broadest, almost every reef throughout the atoll is more or less perfectly ring-formed. Although their presence is thus contingent on the openness of t... |
we shall hereafter see, is included in that of the parent atolls, of which they form the separate portions. 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 i... |
for although only 9 miles in its longest diameter; it has a depth of 39 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 Capt. Moresby, of ... |
a calcareous mud); nearer the border it consists of sand, and in the channels through the reef, of hard sand-banks, sandstone, conglo- merate 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 abrupt... |
depth is considerably greater in the centre than in the channels; but in Tilla-dou-Matte, where the marginal ring-formed reefs stand far apart, the same depth is carried across the entire atoll, from the deep-water line on one side to that on the other. I cannot refrain from once again remarking on the singularity of t... |
concave disk rises abruptly from the unfathomable ocean, with its central expanse studded and its border symmetrically fringed with oval basons of coral-rock, just lipping the surface of the sea, sometimes clothed with vegetation, and each containing a little lake of clear water! In the southern Maldiva atolls, of whic... |
the lagoons come to the surface, and are dry at low water spring-tides; 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 f... |
rest lie at all intermediate depths from the bottom upwards. When treating of the growth of coral I shall again refer to this subject. 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 Capt.... |
strongest, yet the islets are almost all placed on the eastern side of the northern atolls, and on the south-eastern 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 i... |
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 trade wind, the ship-channels into the lagoons are almost invariably situated on the leeward or less expose... |
itself is sometimes either wanting there, or is submerged. A strictly analogous, but different, fact, may be observed at the Maldiva atolls—namely, 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 ... |
atolls, which face S. Male, Phaleedoo, and Moloque atolls, there are seventy-three deep-water channels, and only twenty-five on their outer sides; on the near side of the three latter-named atolls there are fifty-six openings, and only thirty-seven on their outsides. It is scarcely possible to attribute this difference... |
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, b... |
has not been the case with the Maldivas; for we have seen that the islets are placed on the eastern or south eastern 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 stan... |
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 Capt. Moresby, are more constantly exposed than the northern atolls, to a heavy surf. The date of the first formation of some of the islets in this Archipelago is kno... |
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. Capt. Moresby found on one water-washed reef the marks of wells and graves, which were excavated when it s... |
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 Lieut. Prentice found a reef, about six hundred yards in diameter, which the natives positively affirmed was lately an island covered with cocoa-nut trees... |
low water spring tides, and is, (in Lieut. 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 se... |
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 characterized 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 ... |
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 fig. 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 Nillando... |
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 characteriz... |
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 (fig. 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 shew that it is divided by a bifurcating channel, of which the northern arm is about one mile and three quarters in width, with an average depth of 125 fathoms, and the southern one three quarters 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 ring-formed 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 ... |
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 ma... |
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 Tilla-dou-matte. In one part of this atoll, the ring-formed reefs stand so... |
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... |
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 ... |
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 atoll-formed 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 o... |
is given in Plate II., fig. 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 fig. 2, in which the vertical scale has been necessarily exaggerated. Its longest axis is ninety nautical miles, and another line drawn at right an... |
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 littl... |
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... |
fathoms; and off another point, at a somewhat greater distance, there was none with 210 fathoms. Small steep-sided 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 loo... |
II.), although reduced to so small a scale, without at once perceiving that the Great Chagos Bank is, in the words of Capt. Moresby,* "nothing more than a half-drowned atoll." But of what great dimensions, and of how extraordinary an internal structure! We shall hereafter have to consider both the cause of its submerge... |
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, which has produced the bifurcating channel across Mahlos Mahdoo. * This officer has had the kindness to lend me an excellent MS. account ... |
this paper, from the published charts, and from verbal information communicated to me by Capt. Moresby, the above account of the Great Chagos Bank is taken. Closely resemble in general form and structure atoll-reefs—Width and depth of the lagoon-channels—Breaches through the reef in front of valleys, and generally on t... |
constitution of the encircled islands—Number of islands within the same reef—Barrier-reefs of New Caledonia and Australia—Position of the reef relative to the slope of the adjoining land—Probable great thickness of barrier-reefs. THE term 'barrier' has been generally applied to that vast reef which fronts the N.E. shor... |
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 Ne... |
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 miles in nearly a straight line. The geographer Balbi has in effect described those barrier-reefs, which encircle moderately sized islands, by calling them ato... |
resemblance between the reefs of the barrier and atoll classes may be seen in the small, but accurately reduced charts on Plate I.,* and this resemblance can be * The authorities from which these charts have been reduced, together with some remarks on them, are given in a separately appended page, descriptive of the Pl... |
every part of their 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, Cap... |
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, artificial-like breakwater, entirely co... |
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, eve... |
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, (Figs. 1. and 8. Plate I.) it is quite as regular, and of th... |
same average width, as in true atolls. Most barrier-reefs on the inner side slope irregularly into the lagoon-channel, (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... |
Mem. vol. iii. absolutely similar to that described by Chamisso in the Marshall atolls. In the Society Archipelago, Ellis* 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 borde... |
often marshy, alluvial land, from one to four miles in width. This fringe consists of coral-sand and detritus thrown up from the lagoon-channel, 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 accumul... |
the lagoon. At Hogoleu (fig. 2. Plate I.) in the Caroline Archipelago,† the reef on the south side is no less than 20 miles; on the east side, five; and on the north side, 14 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 ... |
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 Keeling atoll. These internal reefs either stand separately, or more commonly skirt the shores of the included high islands. The depth of the lagoon-channel round the S... |
thirty fathoms; in Cook's‡ chart of Ulietea, however, there is one sounding laid down of 48 fathoms: at Vanikoro there are several of 54 and one of 56½ fathoms (English), a depth which even exceeds by a little that of the interior of the great Maldiva atolls. Some barrier-reefs have very few islets on them; whilst othe... |
numerous ones; and those round part of Bolabola (Plate I. fig. 5.) form a single linear strip. The * Consult, on this and other points, the Polynesian Researches by the Rev. W. Ellis, an admirable work, full of curious information. † See Hydrographical Mem. and the Atlas of the Voyage of the Astrolabe, by Capt. Dumont ... |
See the chart in vol. I. of Hawkesworth's 4to ed. of Cook's First Voyage. 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 beneat... |
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 o... |
encircling reef on the leeward side of each of the seven Society Islands, which possess ship-harbours; 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 lagoon-like channel; they generally occur in front of the main valleys, a cir... |
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 barrier-reefs than through the windward side of atolls,—for in atolls there is no inclu... |
is remarkable, that the lagoon-channels 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 co... |
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 breach... |
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 atoll-formed reefs, which carries sediment with it through the deepwater breaches, the same thing probably takes place in barrier-reefs, and this would greatly ai... |
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 Maurua (Plate I. fig. 6.) in the Society group, it has been almost effected, so that there remains only one harbour for small craft. If we look at a set of charts |
of barrier-reefs, 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 barrier-reefs, like atolls, are generally... |
of all sizes, from less than two miles in diameter to sixty miles, (excluding Tilla-dou-Matte, as it consists of a number of almost independent atoll-formed reefs); and there are encircling barrier-reefs from three miles and a half to forty-six miles in diameter,—Turtle Island being an instance of the former, and Hogol... |
36 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 same resemblance in the grouping of atolls and of enci... |
barrier-reefs. The islands lying within reefs of this class, are of very various heights. Tahiti* is 7,000 feet; Maurua about 800; Aituaki 360, and Manouai only 50. The geological nature * The height of Tahiti is given from Capt. Beechey; Maurua from Mr. F. D. Bennett (Geograph. Journ. vol. viii. p. 220); Aitutaki from... |
and Manouai, or Harvey Island, from an estimate by the Rev. J. Williams. The two latter islands, however, are not in some respects well characterized examples of the encircled class. 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... |
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, (fig. 3. Plate I.) both moderately la... |
in one reef. Within the reef of the Gambier group there are four large and some smaller islands (fig. 8. Plate I.); within that of Hogoleu (fig. 2. Plate I.) nearly a dozen small islands are scattered over the expanse of one vast lagoon. After the details now given, it may be asserted, that there is not one point of |
essential difference between encircling barrier-reefs 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 ... |
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 coral-islets, crowned with tall cocoa-nut trees, like one of the many atolls scattered over the Pacific and Indian oceans. The barrier-reefs of Australia and ... |
separate notice from their great dimensions. The reef on the west coast of New Caledonia (fig. 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 twenty-five fathoms deep, with a sandy bottom; but towards ... |
reef is further from the shore, the depth gradually increases to forty, and in some parts to more than sixty fathoms. Flinders* 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 ... |
rare intervals is breached by ship-channels. The sea close outside is profoundly deep; but, in front of the main breaches, soundings can sometimes be obtained. Some low islets have been formed on the reef. There is one important point in the structure of barrier-reefs which must here be considered. The accompanying dia... |
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 fr... |
the hills in the large published charts. It has long been remarked, even from the time of Dampier, that a 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 i... |
submarine prolongation of the land. If we now look at the outer edge of the reef (A A), and bear in mind that the plummet on the right hand represents a depth of 1200 feet, we must conclude that the vertical thickness of these barrier coral reefs is very great. * Flinders' Voyage to Terra Australis, vol. ii. p. 88. |
1—Vanikoro, from the Atlas of the voyage of the Astrolabe, by D. D'Urville. 2—Gambier Island, from Beechey. 3—Maurua, from the atlas of the voyage of the Coquille, by Duperrey. 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 1200 feet... |
the section of the land, and the horizontal shading that of the encircling barrier-reef; from the smallness of the scale, the lagoon-channel could not be represented. A A—Outer edge of the coral-reefs, where the sea breaks. B B—The shore of the encircled islands. I must observe, that if the sections had been taken in a... |
or across other encircled islands,* the result would have been the same. In the succeeding chapter it will be shown that reef-building 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 woo... |
difficulty—how were the basal parts of these barrier-reefs formed. It will, perhaps, occur to some, that the actual reefs formed of coral * In the fifth chapter an East and West section across the Island of Bolabola and its barrier-reefs is given, for the sake of illustrating another point. The unbroken line in it (woo... |
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 lagoon-channel is exaggerated. 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 ... |
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 lagoon-channel, as it does in many instances. On this view,* 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 di... |
and in front of those deep arms of the sea, (as in Raiatea, see Plate II. fig. 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 200 and 300 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 ... |
on its outside, by the accumulation of sediment and coral detritus. Nor, again, can it be asserted, that the reef-building 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 beach. At New Caledonia, (see Plate II. fig. 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 Rev. D. Tyerman and Mr. Bennett (Journ. of Voyage and Travels, vol. i. p. 215) have briefly suggested this explanation of the origin of the |
encircling reefs of the Society Islands. 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 no... |
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 |
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