102 
RATE OF GROWTH. 
CfT. IV. 
atoll in the Caroline group, where every islet, described 
a hundred years before by Cantova, was found in the 
same state by Lutke. 1 For it cannot 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. These 
conditions must depend on many contingencies,- and 
a basis within the requisite depth can rarely be pre- 
sent in the deep oceans where coral formations most 
abound. 
Nor do I think, when we consider the rate of the 
upward growth of reefs under favourable circumstances, 
that we should be influenced by the fact that certain 
submerged reefs, such as those off Tahiti or those within 
Diego Garcia, are not now nearer the surface than they 
were many years ago. For 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 sub- 
merged ; we are, therefore, 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 greatly 
differ in kind on different parts of it, are probably 
1 F. Lulkd’s Voyage autour du Monde. In the group Elato, 
however, 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 
eand. 
