CORAL-REEFS.

IOI

in the Red Sea have not increased during a long intervalof time; or to other such cases, as that of Ouluthy atoll inthe Caroline group, where every islet, described a hundredyears before by Cantova, was found in the same state byLutke, 1 —without it could be shown that, in these cases, theconditions were favourable to the vigorous and unopposedgrowth of the corals living in the different zones of depth,and that a proper basis for the extension of the reef waspresent. The former conditions must depend on manycontingencies, and in the deep oceans where coral forma-tions most abound, a basis within the requisite depth canrarely be present.

Nor do I attach any importance to the fact of certainsubmerged reefs, as those off Tahiti, or those within DiegoGarcia , not now being nearer the surface than they weremany years ago, as an indication of the rate under favourablecircumstances of the upward growth of reefs; after it hasbeen shown, that all the reefs have grown to the surface insome of the Chagos atolls, but that in neighbouring atollswhich appear to be of equal antiquity and to be exposed tothe same external conditions, every reef remains submerged;for we are almost driven to attribute this to a difference, notin the rate of growth, but in the habits of the corals in thetwo cases.

In an old-standing reef, the corals, which are so differentin kind on different parts of it, are probably all adapted tothe stations they occupy, and hold their places, like otherorganic beings, by a struggle one with another, and withexternal nature; hence we may infer that their growth

1 F. Lutke’s Voyage autour du Monde. In the group Elato, how-ever, it appears that what is now the islet Falipi, is called in Cantova’sChart, the Banc de Falipi. It is not stated whether this has beencaused by the growth of coral, or by the accumulation of sand.