When merely the surface of an island of ordinary formation is strewed with marine bodies, and that continuously, or nearly so, 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 coral-rock, 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 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 surrounded by a terrace-like 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 coral-rock, "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 coral-rock. 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 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 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 lagoon-islands), coral-rock, like that on the beach, was found. In the NAVIGATOR ARCHIPELAGO, Mr. Couthouy ("Remarks on Coral-Formations," page 50.) 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 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. Couthouy. Earthquakes 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 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.