Narrative of the surveying voyages of his majesty's ships Adventure and Beagle (vol.3)

562 CORAL FORMATIONS. April, 1836. remarka1)le 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 kinds of reef. If there had been space, I should have made a few gene- ral remarks, before entering into any detail. I may, how- ever, just notice the remarkable absence of the reef-build- ing polypi over certain wide areas within the tropical sea for instance, on the whole west coast of America, 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 adjoin- ing 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 Archii^elagoes. 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