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Show 562 CORAL FORMATIONS. April, 1836. remarkable degree ; and that certain laws may be inferred from the examination, of far more importance than . the mere explanation of the origin of the circular or other kmds of reef. If there had been space, I should have made a few gene-ral remarks, before entering ii,ltO any detail. I may, .h~wever, just notice the remarkable absen?e of the r~ef-bullding polypi over certain wide areas withm the. tropical sea: for instance, on the whole west coast of Amenca, and, as I believe, of Africa (?), and round the eastern islands in the Atlantic ocean. Although certain species of lamelliform zoophytes are found on the shores of the latter islands, and though calcareous matter is abundant to excess, yet reefs are never formed. It would appear that the effective species do not occur there; of which circumstance I apprehend no explanation can be given, any more than why it has been ordained that certain plants, as heaths, should be absent from the New World, although so common in the Old. Without entering into any minute geographical details, I must observe, that the usual direction of the island groups in the central parts of the Pacific, is N.W. and S.E. This must be noticed, because subterranean disturbances are known to follow the coast lines of the land. Commencing on the shores of America, there are abundant proofs that the greater part has been elevated within the recent period, but as coral reefs do not occur there, it is not immediately connected with our present subject. Immediately adjoining the continent there is an extent of ocean remarkably free from islands, and where of course there exists no possible indication of any change of level. We then come to a N · W · by W. line dividing the open sea from one strewed with lagoon islands, and including the two beautiful groups of encircled islands the Society and Georgian Archipelagoes. This great band having a length of more than four thousand miles by six hundred broad must, according to our view, be an area of subsidence. We will at present for convenience sake April, 1836. A REAS OF A LTERNATE MOVEME NTS, 563 pass over the space of ocean immediately adjoining it, and proceed to the chain of islands including the New Hebrides, Solomon, and New Ireland. Any one who e:x:amines the charts of the separate isl:J.nds in the Pacific, engraved on a large scale, will be struck with the absence of all distant or encircling reefs round these groups : yet it is known that coral occurs abundantly close in shore. Here, then, according to the theory, there are no proofs of subsidence; and in conformity to this we find in the works of Forster, Lesson, Labillardiere, Quoy, and Bennett, constant allusion to the masses of elevated coral. These islands form, therefore, a well-determined band of elevation: between it and the great area of subsidence first mentioned there is a broad space of sea irregularly scattered with islets of all classes; some with proofs of recent elevation and merely fringed by reefs ; others encircled; and some lagoon islands. One of the latter is described by Captain Cook as a grand circle of breakers without a single spot of land ; in this case we may believe that an ordinary lagoon island has been recently submerged. On the other hand, there are proofs of other lagoon islands having been lifted up several yards above the level of the sea, but which still retain a pool of salt water in their centres. These facts show an irregular action in the subterranean forces; and when we remember that the space lies directly between the well-marked area of elevation and the enormous one of subsidence, an alternate and irregular movement seems almost probable. To the westward of the New Hebrides line of elevation we have New Caledonia, and ' the space included between it and the Australian barrier, which Flinders, on account of the number of reefs, proposed to call the Corallian Sea. It is bounded on two sides by the grandest and most extraordinary reefs in the world, and is likewise terminated to the northward by the coast of Louisiade,-most dangerous on account of its distant reefs. This, then, according to our theory, is an area of subsidence. I may here remark, that as the Barrier is supposed to be produced by the subsidence 2 0 2 |