72 CORAL-REEFS. 



from their outer edges to the foundation on which they 

 rest (from AA in the section to the dotted lines), is really 

 great ; but in this, there is no difficulty, for it is not 

 necessary to suppose that the coral has sprung up from an 

 immense depth, as will be evident when the theory of the 

 upward growth of coral-reefs, during the slow subsidence of 

 their foundation, is discussed. 



