CORAL-REEFS. 101 



in the Red Sea have not increased during a long interval 

 of time \ or to other such cases, as that of Ouluthy atoll in 

 the Caroline group, where every islet, described a hundred 

 years before by Cantova, was found in the same state by 

 Lutke', 1 — without it could be shown that, in these cases, the 

 conditions were favourable to the vigorous and unopposed 

 growth of the corals living in the different zones of depth, 

 and that a proper basis for the extension of the reef was 

 present. The former conditions must depend on many 

 contingencies, and in the deep oceans where coral forma- 

 tions most abound, a basis within the requisite depth can 

 rarely be present. 



Nor do I attach any importance to the fact of certain 

 submerged reefs, as those off Tahiti, or those within Diego 

 Garcia, not now being nearer the surface than they were 

 many years ago, as an indication of the rate under favourable 

 circumstances of the upward growth of reefs ; after it has 

 been shown, that all the reefs have grown to the surface in 

 some of the Chagos atolls, but that in neighbouring atolls 

 which appear to be of equal antiquity and to be exposed to 

 the same external conditions, every reef remains submerged ; 

 for we are almost driven to attribute this to a difference, not 

 in the rate of growth, but in the habits of the corals in the 

 two cases. 



In an old-standing reef, the corals, which are so different 

 in kind on different parts of it, are probably all adapted to 

 the stations they occupy, and hold their places, like other 

 organic beings, by a struggle one with another, and with 

 external 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's 

 Chart, the Banc de Falipi. It is not stated whether this has been 

 caused by the growth of coral, or by the accumulation of sand. 



