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GEOLOGICAL SOCIETY.

May 31.—Rev. W. Whewell, President, in the chair.—A paper was first read, on certain areas of elevation and of subsidence in the Pacific and Indian Oceans, as deduced from the study of coral formations, by C. Darwin, Esq., F.G.S.

The author first notices the most remarkable points in the structure of Lagoon Islands, and shows that the lamelliform corals do not grow at any great depths—indeed, beyond ten fathoms; the bottom generally consisting of calcareous sand, or of masses of dead coral rock, He then noticed the "encircling reefs," which form a ring round mountainous islands at the distance of two or three miles, and which also encircle the submarine prolongation of islands, as the double line of reef extending 140 miles beyond the island of Caledonia. Again, the barrier reef, as that parallel to the north-east coast of Australia, forms a third class of coral formations. These three classes of reefs—encircling, barrier, and lagoon—are very similar in formation. A distinct class of reefs was also pointed out by the author, called by him "fringing reefs," which extend only so far from the shore that there is no difficulty in understanding their growth.

The theory which Mr. Darwin then offered, so as to include every kind of structure, is simply, that as the land with the attached reefs subsides very gradually from the action of subterranean causes, the coral-building polypi soon again raise their solid masses to the level of the water; but not so with the land: each inch lost is irreclaimably gone; as the whole gradually sinks, the water gains foot by foot on the, shore, till the last and highest peak is finally sub-merged. The author then proceeded to offer some considerations on the probability of general subsidences in the Pacific, where many causes tend to its production, and the difficulty of explaining the existence of a vast number of reefs on one level, unless we suppose that one mountain top after another becomes submerged, the zoophytes always bringing up their stony masses to the surface of the water. Subsidence being granted, it was shown that a fringing reef would be converted by the upward growth of the coral, into one of the encircling order; and thus, by the disappearance of the central land into a lagoon island. After adducing some proofs of subsidence in Keeling and Vanikoro Islands, and of elevation in Sumatra, the author proceeds to show that as continental elevations act over wide areas, so might we suppose continental subsidences would do; and in conformity to these views, that the Pacific and Indian Seas could be divided into symmetrical areas of the two kinds; the one sinking, as deduced from the presence of encircling and barrier reefs, and lagoon islands; and the other rising, as known from uplifted shells and corals, and skirting reefs. The absence of lagoon islands in certain tracts, such as in both the West and East Indies, Red Sea. &c., was thus easily explained, for proofs of recent elevation are there described.

Mr. Darwin then pointed out the above areas in the Pacific and Indian Oceans, and deduced as important consequences—1. That linear spaces, of great extent, are undergoing movements of an astonishing uniformity, and that the lands of elevation and subsidence alternate, 2. That the points of volcanic eruption all fall on the areas of elevation. 3. That the geographical distribution of plants is elucidated by the discovery of former centres, whence the germs could be disseminated. 4. That some degree of light might thus be thrown on the question whether certain groups of living beings, peculiar to small spots, are the remnants of a former large population, or a new one springing into existence;¹ and lastly, when beholding more than a hemisphere divided into symmetrical areas, which, within a limited period of time, have undergone certain known movements, we obtain some insight into the system, by which the crust of the globe is modified during the endless cycle of changes.

¹ This is Darwin's first published reference to his interest in the origin of species.