192 EECAPITULATION. Ch. VI. 



chains of mountains of almost exactly the same height 

 extending over many thousand square miles, there is 

 but one alternative ; namely, the prolonged subsidence 

 of the foundations on which the atolls first became 

 attached, together with the upward growth of the 

 reef-constructing corals. On this view every difficulty 

 vanishes : fringing-reefs are thus easily converted into 

 barrier-reefs; and barrier-reefs into atolls, as soon as 

 the last pinnacle of land sinks beneath the surface of 

 the sea. 



The wall-like structure on the inner sides of atolls 

 and barrier-reefs — the bason or ring-like shape of the 

 marginal and central reefs in the Maldiva atolls — the 

 union of some atolls as if by a ribbon — the apparent 

 disseverment of others — the ordinary outline of groups 

 of atolls and their forms — are all thus explained. We 

 thus understand the occurrence in both atolls and 

 barrier-reefs of portions, or of the whole, in a dead and 

 submerged condition, though still retaining the outline 

 of a living reef. The existence of breaches through 

 barrier-reefs in front of valleys, though separated from 

 them by wide spaces of deep water, can be similarly 

 explained. It confirms our theory that we find the 

 two kinds of reefs formed through subsidence generally 

 situated near each other and at a distance from the spaces 

 where fringing-reefs abound. On searching for other 

 evidence of the movements assumed by the theory, 

 we find marks of change in atolls and in barrier-reefs, 

 and of subterranean disturbances beneath them ; but 

 from the nature of things, it is scarcely possible to 



