148 CORAL-REEFS. 



the theory ; and if this can be satisfactorily shown, not 

 only is the theory confirmed, but as deductions, the answers 

 are in themselves important Under this latter point of 

 view, these questions will be chiefly considered in the 

 following chapter. 1 



1 I may take this opportunity of briefly considering the appearances, 

 which would probably be presented by a vertical and deep section 

 across a coral formation (referring chiefly to an atoll), formed by the 

 upward growth of coral during successive subsidences. This is a 

 subject worthy of attention, as a means of comparison with ancient 

 coral-strata. The circumferential parts would consist of massive 

 species, in a vertical position, with their interstices filled up with 

 detritus; but this would be the part most subject to subsequent denuda- 

 tion and removal. It is useless to speculate how large a portion of the 

 exterior annular reef would consist of upright coral, and how much of 

 fragmentary rock, for this would depend on many contingencies, — 

 such as on the rate of subsidence, occasionally allowing a fresh growth 

 of coral to cover the whole surface, and on the breakers having force 

 sufficient to throw fragments over this same space. The conglomerate 

 which composes the base of the islets, would (if not removed by 

 denudation together with the exterior reef on which it rests) be con- 

 spicuous from the size of the fragments, — the different degrees in which 

 they have been rounded, — the presence of fragments of conglomerate 

 torn up, rounded, and recemented, — and from the oblique stratification. 

 The corals which lived in the lagoon-reefs at each successive level, 

 would be preserved upright, and they would consist of many kinds, 

 generally much branched. In this part, however, a very large propor- 

 tion of the rock (and in some cases nearly all of it) would be formed of 

 sedimentary matter, either in an excessively fine, or in a moderately 

 coarse state, and with the particles almost blended together. The 

 conglomerate which was formed of rounded pieces of the branched 

 corals, on the shores of the lagoon, would differ from that formed on 

 the islets and derived from the outer coast; yet both might have 

 accumulated very near each other. I have seen a conglomerate lime- 

 stone from Devonshire like a conglomerate now forming on the shores 

 of the Maldiva atolls. The stratification taken as a whole, would be 

 horizontal; but the conglomerate beds resting on the exterior reef, and 

 the beds of sandstone on the shores of the lagoon (and no doubt on the 



