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Updated: June 24, 2025
The deposition, moreover, of sediment, checks the growth of coral-reefs, so that these two agencies cannot act together with full effect in filling it up.
The uncoloured coasts consist, first and chiefly, of those, where there are no coral-reefs, or such small portions as to be quite insignificant.
There are no coral-reefs in the GALAPAGOS Archipelago, as I know from personal inspection; and I believe there are none on the COCOS, REVILLA-GIGEDO, and other neighbouring islands. CLIPPERTON rock, 10 deg N., 109 deg W., has lately been surveyed by Captain Belcher; in form it is like the crater of a volcano. From a drawing appended to the MS. plan in the Admiralty, it evidently is not an atoll.
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.
The horizontal line is the level of the sea, from which on the right hand a plummet descends, representing a depth of 200 fathoms, or 1,200 feet. The vertical shading shows the section of the land, and the horizontal shading that of the encircling barrier-reef: from the smallness of the scale, the lagoon-channel could not be represented. AA. Outer edge of the coral-reefs, where the sea breaks.
As Kotzebue and subsequently Darwin have pointed out, all the islands of the Pacific are either coral-reefs or of volcanic origin; and many of these rise from great depths; that is to say, from depths of 1000 to 2000 fathoms.
None of these remains have been specifically examined. On the coast, where masses of coral-rock would have afforded the clearest evidence, I looked in vain for any signs of recent elevation. For references to the above authorities, and for more detailed reasons for not believing that Tahiti has been recently elevated, I must refer to the "Structure and Distribution of Coral-Reefs."
Soon after we made the Cuban coast, and stood to the westward, hoping to sight something which would determine our position. After a run of some hours just outside of the coral-reefs, we sighted in the distance some vessels at anchor. As we approached, a large town was visible at the head of the bay, which proved to be Cardenas.
So it is not found in the cold depths of the sea, nor in the seas near our islands, but in the warm shallow waters near tropical lands it flourishes so well that it builds up most wonderful Coral walls. So strong are they that they can defy the terrific force of the waves. Some coral-reefs are of immense size and strength. One, near the coast of Australia, is nearly a thousand miles in length.
There is, however, not much foundation for this view; for nowhere are coral-reefs more extensive than on the shores of New Caledonia, and of north-eastern Australia, which consist of primary formations; and in the largest groups of atolls, namely the Maldiva, Chagos, Marshall, Gilbert, and Low Archipelagoes, there is no volcanic or other kind of rock, excepting that formed of coral.
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