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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 coral-rock, (associated with some basalt in Mangaia), and the sixth as lofty and basaltic. Mangaia is nearly 300 feet high, with a level summit; and according to Mr. S. Wilson... |
upraised reef; "and there are in the central hollow, formerly the bed of the lagoon, many scattered patches of coral-rock, some of them raised to a height of forty feet." These knolls of coral-rock were evidently once separate reefs in the lagoon of an atoll. Mr. Martens, at Sydney, informed me that this island is surr... |
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‡ describes the plant... |
of * Beechey's Voyage in the Pacific, p. 46, 4to. edition. † Couthouy's Remarks, p. 34. ‡ Observations made during Voyage round the World, p. 147. the dead, but still upright and spreading trees of coral; and the younger Forster* believes that an ancient lagoon is now represented by a central plain: here we cannot doub... |
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 coral-ro... |
and irregularities worn into it by the action of the tides."† On Eoua the same appearances were noticed at an elevation of between 200 and 300 feet. Vavao, also, at the opposite or northern end of the group, consists, according to the Rev. J. Williams, of coral-rock. Tongatabou, with its northern extensive reefs, resem... |
half originally imperfect, or one unequally elevated; and Anamouka, an atoll equally elevated. This latter island contains‡ in its centre a salt-water lake, about a mile-and-a-half in diameter, without any communication with the sea, and around it the land rises gradually like a bank: the highest part is only between t... |
as on the rest of the land, (which as Cook observes, rises above the height of true lagoon-islands,) coral-rock like that on the beach, was found. In the Navigator Archipelago, Mr. Couthouy§ found on Manua many and very large fragments of coral at the height of eighty feet, "on a steep hill-side, rising half a mile inl... |
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... |
are very frequent in this archipelago. 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 Salomon Archipelago, I have n... |
forms the northern point of the latter chain, both Labillardière and Lesson have described large beds of an apparently very modern * Voyage, vol. ii. p. 163. † Cook's Third Voyage (4to. edition), vol. i. p. 314. ‡ Ibid. vol. I. p. 235. § Remarks on Coral Formations, p. 50. madreporitic rock, with the form of the corals... |
The latter author* 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, Tinian, Saypan, and some islets farther north, are described... |
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... |
this part of the sea which is fringed; it is ninety feet high, and consists entirely of madreporitic rock.§ In the East Indian Archipelago, many authors have recorded proofs of recent elevation. M. Lesson|| states, that near Port Dory, on the north coast of New Guinea, the shores are flanked, to the height of 150 feet,... |
a modern date. He mentions similar formations at Waigiou, Amboina, Bourou, Ceram, Sonda and Timor: at this latter place, MM. Quoy and Gaimard¶ 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** to resemble small co... |
with existing species, had a recent appearance. Dr. Ward describes in this neighbourhood (Trans. Asiat. Soc. vol. xviii., part 2, p. 166.) a single water-worn rock, with a conglomerate of sea shells at its base, situated six miles inland, which, according to the traditions of the natives, was has described some upraise... |
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 water-washed rocks, present appearances,* (although it i... |
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 Phillippines, found near Cabagan, in Luzon, about fifty feet above the leve... |
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† of the lines of inland reefs, and walls of coral-rock worn into caves, above the pres... |
the waves, at the Loo Choo Islands, there can be little doubt that they have been upraised at no very remote period. Dr. Davy‡ describes the northern province of Ceylon 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.§ once surrounded by the sea. Capt. Low has also described (Ibid. Part i. p. 131.) mounds of shells lying two miles inland ... |
coast. * Notices of the East Indian Arch., Singapore, 1828, p. 6, and Append. p. 43. † Capt. B. Hall, Voyage to Loo Choo, Append. pp. xxi. and xxv. Capt. Beechey's Voyage, p. 496. ‡ Travels in Ceylon, p. 13. This madreporitic formation is mentioned by M. Cordier in his report to the Institute, (May 4, 1839,) on the voy... |
of the Chevrette, as one of immense extent, and belonging to the latest tertiary period. § Dr. Benza, in his Journey through the N. Circars, (the Madras Lit. and Scient. Journ. vol. v.) has described a formation with recent freshwater and marine shells, occurring at the distance of three or four miles from the present ... |
with me, attributed their position to a rise of the land. Dr. Malcolmson, how- Mauritius has certainly been upraised within the recent period, as I have stated in the chapter on fringing-reefs. The northern extremity of Madagascar is described by Capt. Owen* as formed of madreporitic rock, as likewise are the shores an... |
Eastern Africa, from a little north of the equator for 900 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... |
front of the coast from the equator to 2° S., without feeling convinced that a line of fringing reefs 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, ... |
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 our fringed class. The nature of the formations round the shores of the Re... |
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 barrier-reefs; on which circumstance I shall presently make some remarks. Rüppell† states that the tertiary formation, of which he has exa... |
along the shores with a uniform height of from 30 and 40 feet, from the mouth of the Gulf of Suez to about Lat. 26°; but that south of 26°, the beds attain only the height of from 12 to 15 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 (Lat. 15° 30' S.) shells and corals, apparently recent, at a ever, (and there cannot be a higher authority on the geology of India) informs me that he suspects that these beds may have been f... |
by the mere action of the waves and currents accumulating sediment. From analogy I should much incline to Dr. Benza's opinion. * Owen's Africa, vol. ii. p. 37 for Madagascar; and for S. Africa, vol. i. pp. 412 and 426. Lieut. Boteler's narrative contains fuller particulars regarding the coral-rock, vol. i. p. 174., and... |
See also Ruschenberger's Voyage round the World, vol. i. p. 60. † Rüppell, Reise in Abyssinien, Band i. s. 141. height between 30 and 40 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 ... |
that on which Dr. Rüppell says that the modern beds attain a height of only 30 to 40 feet, Mr. Burton* found a deposit replete with existing species of shells, at the height of 200 feet. In an admirable series of drawings by Capt. Moresby, I could see how continuously the cliff-bounded low plains of this formation exte... |
nearly equable height, both on the eastern and western shores. The southern coast of Arabia seem 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 coral reefs; but as it is difficu... |
shallow sea, I have coloured only some near the mouth; towards the head of the gulf Mr. Ainsworth† 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 lat... |
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.‡ It is very remarkable, on reviewing these details, to observe in how many instances fringing-reefs round the shores, have coincided with the existence on the la... |
* Lyell's Principles of Geology, 5th edition, vol. iv. p. 25. † Ainsworth's Assyria and Babylon, p. 217. ‡ On Florida and the north shores of the Gulf of Mexico, Rogers' Report to Brit. Assoc. vol. iii. p. 14.—On the shores of Mexico, Humboldt, Polit. Essay on New Spain, vol. i. p. 62. (I have also some corroborative f... |
vol. xi. p. 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 might have added many other less important references. remains, which seem, from evidence more or less satisfactory, to belong to a late tertiary period. It may, however, be object... |
of elevation, perhaps, occur on the coasts coloured blue in our map: but this certainly is not the case with the few following and doubtful exceptions. 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... |
in the middle part, as barrier-reefs; should, however, the statements prove accurate of the less height of the tertiary beds 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.... |
shells and corals high up on the mountains of the Society Islands,—a group encircled by barrier-reefs, and, therefore, supposed to have subsided: at Tahiti Mr. Stutchbury found on the apex of one of the highest mountains, between 5000 and 7000 feet above the level of the sea, "a distinct and regular stratum of semi-fos... |
as well as myself, have searched in vain at a low level near the coast, for upraised shells or masses of coral-reef, 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 volc... |
subsequently been washed * Ellis, in his Polynesian Researches, was the first to call attention to these remains, (vol. i. p. 38.) and the tradition of the natives concerning them. See also William's, Nar. of Miss. Enterprize, p. 21; also Tyerman and G. Bennett, Journ. of Voyage, vol. i. p. 213; also Mr. Couthouy's Rem... |
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 Journ. No. 1. p. 54. There is a passage in Von Zach, Corres. Astronom. vol. x. p. 266., inferring an uprising at Tahiti, from a footpath now used, which was formerly im... |
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. 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... |
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 ... |
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... |
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 coral-rock; but I have no evidence of their recent elevation, besides, the improbability of Mangaia, a fringed island in t... |
distant 170 miles,) having retained its nearly perfect atoll-like 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 barrier-reefs are there not well characterize... |
to be surprised at oscillations of level of this kind having occasionally taken place. There can be scarcely any doubt that Savage, Aurora,* and Mangaia Islands, and several of the * Aurora Island is described by Mr. Couthouy (Remarks, p. 58); it lies 120 miles N.E. of Tahiti; it is not coloured in the appended map, be... |
appear to be fringed by living reefs. Mr. Couthouy describes its summit as "presenting a broad table-land which declines a few feet towards the centre, where we may suppose the lagoon to have been placed." It is about 200 feet in height, and consists of reef-rock and conglomerate, with existing species of coral embeded... |
elevated at two successive periods; the cliffs being 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, in... |
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 exactly in... |
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 high, and at the same time not surrounded |
by an encircling barrier-reef. On the absence of active Volcanos in the areas of subsidence, and on their frequent presence in the areas of elevation.—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 volcanos his... |
It is impossible not to be struck, first with the absence of volcanos 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;... |
of the principal volcanic chains with the parts coloured red, which indicates the presence of fringing reefs; 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 marked half-way up with a horizontal water-worn ... |
Island seems closely to resemble in structure Elizabeth Island, at the southern end of the Low Archipelago. volcanos were added to the map, or indeed before I knew of the existence of several of them. The volcano in Torres Strait, at the northern point of Australia, is that which lies nearest to a large subsiding area,... |
within the outer margin of the actual barrier-reef. The Great Comoro Island, which probably contains a volcano, is only twenty miles distant from the barrier-reef of Mohila; Ambil volcano, in the Philippines, is distant only a little more than sixty miles from the atoll-formed Appoo reef: and there are two other volcan... |
coloured blue. These few cases, which thus offer partial exceptions to the rule, of volcanos 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 o... |
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 volcanos, and, perhaps, others,* are known to be in action: on the other h... |
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 volcanos had come into action, and had become extinguished on the same spots, according as the elev... |
prevailed. There are some other coasts on the map, where volcanos in a state of action concur with proofs of recent elevation, besides those coloured red from being fringed by coral-reefs. 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 vol... |
world, from near the equator for a space of between 2000 and 3000 miles * See the note at p. 121, on the authorities for colouring the volcanos in the appended map. southward, has undergone an upward movement during a late geological period. The islands on the north-western shores of the Pacific, which form the second ... |
very imperfectly known; but Luzon, in the Philippines, and the Loo Choo islands, have been recently elevated; and at Kamtschatka* 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 volcanos. The co-existe... |
with upraised beds of a modern tertiary origin, will occur to every geologist.† Nevertheless, until it could be shown that volcanos 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 n... |
considered as almost established, that volcanos 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.‡ ... |
Elevation.—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 exis- * At Sedanka, in Lat. 58° N. (Von Buch's Descrip. des isles Canaries, p. 455... |
I shall give the evidence referred to with respect to the elevation of New Zealand. † During the subterranean disturbances which took place in Chile in 1835, I have shown (Geolog. Trans. 2nd Ser. vol. v. p. 606.) that at the same moment that a large district was upraised, volcanic matter burst forth at widely-separated... |
old vents. ‡ 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 earth's surface, and certainly no movement of subsidence. tence of continents shows that the areas ... |
at some period have been upraised: in South America we may feel sure, and on the north-western 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,... |
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... |
the Marshall Archipelago,—a length of 4500 miles, in which, as far as is known, every island, excepting Aurora which lies just without the Low Archipelago, is atoll-formed. 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,... |
lies the most broken land on the globe, and there the rising parts are surrounded and penetrated by areas of subsidence,* so that the prevailing movements now in progress, seem to accord with the actual states of surface of the great divisions of the world. The blue spaces on the map are nearly all elongated; but it do... |
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... |
a chain of atolls and barrier-reefs lies in an elongated area, between spaces coloured red, which therefore have re- * I suspect that the Arru and Timor-laut 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 i... |
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... |
which subsided during the formation of the great north and south line of atolls in the Indian Ocean,—of the east and west line of the Caroline atolls,—and of the north-west and south-east line of the barrier-reefs of New Caledonia and the Louisiade, must have originally been elongated, or if not so, they must have sinc... |
which we know to belong to a recent period. I infer from Mr. Hopkins's researches,* 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. Mountain-chains, however, when already formed, altho... |
may be raised together by a widely-acting force: so, perhaps, mountain-chains 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 * Resea... |
part i. † For instance in S. America from lat. 34° for 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 ... |
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. mountain-lines, namely the Sierra Ventana and the S. Tapalguen, and the great north and south line of the Cordillera have been together raised. In the West Indies the N. and S. line of the eastern Antilles, ... |
and W. line of Jamaica, appear both to have been upraised within the latest geological period. 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 th... |
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 table-land, proves that large surfaces have been upraised in mass to considerable heights above the level of the ocean; alth... |
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 forme... |
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 littoral shells and pebbles, all requiring time for their production, prove that these movements have been very slow; we can, however, infer this ... |
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,... |
from each other by long intervals of time, during which the reef-constructing polypifers were able to bring up their solid frame-works 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 geo... |
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... |
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, t... |
some large areas to rise, and others to subside, have acted in a very similar manner. Recapitulation.—In the three first chapters, the principal kinds of coral-reefs 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 b... |
land within its central expanse; and a barrier-reef differs from a fringing-reef, 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 deep-water lagoon-like space or moat within the reef. In the fourth chapter the grow... |
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 fringing-reefs are based; whereas, with barrier-reefs and atolls, there is a great apparent difficulty on this head;—in barrier-reefs from the improbabilit... |
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 mountain-summits, which, although rising very near to the surface-level of the sea, in no one instance em... |
admission, which implies the existence of submarine chains of mountains of almost the same height, extending over areas of many thousand square 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 reef-... |
converted into barrier-reefs; and barrier-reefs, when encircling islands, are thus converted into atolls, the instant the last pinnacle of land sinks beneath the surface of the ocean. Thus the ordinary forms and certain peculiarities in the structure of atolls and barrier-reefs can be explained;—namely, the wall-like s... |
central reefs in the Maldiva atolls—the union of some atolls as if by a ribbon—the apparent disseverment of others—and the occurrence, in atolls as well as in barrier-reefs, 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 explain... |
through barrier-reefs 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 separ... |
abound. On searching for other evidence of the movements supposed by our theory, we find marks of change in atolls and in barrier-reefs, 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 i... |
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 generally been elevated. Finally, when the two great types of structure, namely barrier-reefs and atolls on the one hand, and... |
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