126

CORAL-REEFS.

believed by the residents to have been washed by the rainthrough the broken masses of underlying rock; the islandwas thus rendered unproductive. Chamisso 1 states, thatearthquakes are felt in the Marshall atolls, which are farfrom any high land, and likewise in the islands of theCaroline Archipelago. On one of the latter, namelyOulleay atoll, Admiral Lutk6, as he had the kindness toinform me, observed several straight fissures about a foot inwidth, running for some hundred yards obliquely across thewhole width of the reef. Fissures indicate a stretching ofthe earth’s crust, and, therefore, probably changes in itslevel; but these coral-islands, which have been shaken andfissured, certainly have not been elevated, and, therefore,probably they have subsided. In the chapter on Keelingatoll, I attempted to show by direct evidence, that theisland underwent a movement of subsidence, during theearthquakes lately felt there.

The facts stand thus;—there are many large tracts ofocean, without any high land, interspersed with reefs andislets, formed by the growth of those kinds of corals, whichcannot live at great depths; and the existence of thesereefs and low islets, in such numbers and at such distantpoints, is quite inexplicable, excepting on the theory, thatthe bases on which the reefs first became attached, slowlyand successively sank beneath the level of the sea, whilstthe corals continued to grow upwards. No positive factsare opposed to this view, and some general considerationsrender it probable. There is evidence of change in form,whether or not from subsidence, or some of these coral-islands ; and there is evidence of subterranean disturbancesbeneath them. Will then the theory, to which we have

] See Chamisso , in Kotzebue’s First Voyage, vol. iii. pp. 182 and

136.