CHAPTER XX. KEELING ISLAND: - CORAL FORMATIONS
Taking a final view of the map, and bearing in mind the statements made with respect to the upraised organic remains, we must feel astonished at the vastness of the areas, which have suffered changes in level either downwards or upwards, within a period not geologically remote. It would appear also, that the elevatory and subsiding movements follow nearly the same laws. Throughout the spaces interspersed with atolls, where not a single peak of high land has been left above the level of the sea, the sinking must have been immense in amount. The sinking, moreover, whether continuous, or recurrent with intervals sufficiently long for the corals again to bring up their living edifices to the surface, must necessarily have been extremely slow. This conclusion is probably the most important one which can be deduced from the study of coral formations; - and it is one which it is difficult to imagine how otherwise could ever have been arrived at. Nor can I quite pass over the probability of the former existence of large archipelagoes of lofty islands, where now only rings of coral-rock scarcely break the open expanse of the sea, throwing some light on the distribution of the inhabitants of the other high islands, now left standing so immensely remote from each other in the midst of the great oceans. The reef-constructing corals have indeed reared and preserved wonderful memorials of the subterranean oscillations of level; we see in each barrier-reef a proof that the land has there subsided, and in each atoll a monument over an island now lost. We may thus, like unto a geologist who had lived his ten thousand years and kept a record of the passing changes, gain some insight into the great system by which the surface of this globe has been broken up, and land and water interchanged.
 These Plants are described in the Annals of Nat. Hist., vol. i., 1838, p. 337.
 Holman's Travels, vol. iv. p. 378.
 Kotzebue's First Voyage, vol. iii. p. 155.
 The thirteen species belong to the following orders: - In the Coleoptera, a minute Elater; Orthoptera, a Gryllus and a Blatta; Hemiptera, one species; Homoptera, two; Neuroptera a Chrysopa; Hymenoptera, two ants; Lepidoptera nocturna, a Diopaea, and a Pterophorus (?); Diptera, two species.
 Kotzebue's First Voyage, vol. iii. p. 222.
 The large claws or pincers of some of these crabs are most beautifully adapted, when drawn back, to form an operculum to the shell, nearly as perfect as the proper one originally belonging to the molluscous animal. I was assured, and as far as my observations went I found it so, that certain species of the hermit-crab always use certain species of shells.
 Some natives carried by Kotzebue to Kamtschatka collected stones to take back to their country.
 See Proceedings of Zoological Society, 1832, p. 17.
 Tyerman and Bennett. Voyage, etc. vol. ii. p. 33.
 I exclude, of course, some soil which has been imported here in vessels from Malacca and Java, and likewise, some small fragments of pumice, drifted here by the waves. The one block of greenstone, moreover, on the northern island must be excepted.
 These were first read before the Geological Society in May, 1837, and have since been developed in a separate volume on the "Structure and Distribution of Coral Reefs."
 It is remarkable that Mr. Lyell, 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.
 It has been highly satisfactory to me to find the following passage in a pamphlet by Mr. Couthouy, one of the naturalists in the great Antarctic Expedition of the United States: - "Having personally examined a large number of coral-islands and resided 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." - The naturalists, however, of this expedition differ with me on some points respecting coral formations.