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Show IMBEDDING OF MARINE TESTACEA. fCh.XVII. animals abound is very considerable. Captain Vidal ascertained, by soundings lately made off rl'ory island, on the north. west coast of Ireland, that crustacea, star-fish, and testacea, occurred at various depths between fifty and one hundred fathoms; and in the tropics testacea and zoophytes have been found still deeper. During the survey of the west coast of Africa, now in progress, Captain Belcher found, by frequent soundings between the twenty-third and twentieth degrees of north latitude, that the bottom of the sea at the depth of from twenty to about fifty fathoms, consists of sand, with a great intermixture of shells often entire, but sometimes finely comminuted. Between tho eleventh and ninth degrees of north latitude, on the same coast, at soundings varying from twenty to about eighty fathoms, he brought up abundance of corals and shells mixed with sand. These also were in some parts entire, and in others worn and broken. In all these cases it is only necessary that there should be some deposition of sedimentary matter, however minute, such as may be supplied by rivers or currents preying on a line of cliffs, and stratified formations, hundreds of feet in thickness, will result in the course of ages, containing throughout organic remains, in a more or less perfect state of preservation. CHAPTER XVIII. Formation of coral reefs-They are composed of shells as well as corals-Conversion of a submerged reef into an island-Extent and thickness of coral formations- The Maldiva isles-Growth of coral not rap1"d - Its geo 1o g1· ca1 1· mpor t ance-c·l r• cular and oval forms of coral islands-Shnpe ofthe"r 1 c f ih · • • ... 1 agoons-- auses o e.r ~e:uhar configuration-Openings into the lagoons-Why the windward side both m Islands and submerged reefs is higher than the leeward-Stratification of coral formati~ns-Exte~t of some reefs in the Pacific-That the subsidence by earth· quakes m the Pac1fic, exceeds the elevation due to the same cause--Elizabeth or Henderson' s Island-Coral and ·s hell lirnestones no w m· progress, excee d 1· n' area any known group of ancient rocks-The theory that all limestone is of animal origin considered-The hypothesis that the quantity of calcareous matter has been and is still on the increase, conhoverted. Corals and Coral reefs. THE powers of the organic creation in modifying the form and st~·ucture of those ~arts of .the earth's crust, which may be sa1d to be undergomg repair, or where new rock-formations ~re continually in progress, are most conspicuously displayed m the labours of the coral animals. We may compare the operation of these zoophytes in the ocean, to the effects produced on a smaller scale upon the land, ·by the plants which generate peat. In the case of the Sphagnum, the upper part vegetates while the lower portion is entering into a mineral mass, where the traces of organization usually remain, but in which life has entirely ceased. In the corals, in like manner, the more durable materials of the generation that has passed away, serve as the foundation on which living animals are con. tinuing to rear a similar structure. The calcareous masses usually termed coral reefs, are by no means exclusively composed of zoophytes, but also a great variety of shells ; some of the largest and heaviest of known species contributing to augment the mass. In the south Pacific, great beds of oysters, mussels, pinn(l! marin(l!, and other shells, cover in. great profusion almost every reef; and, on the beach |