144 THEORY OF THE FORMATION Ch. V. 



naturally follow from continued subsidence, combined 

 with the upward growth of reefs fronting one side alone 

 of a high island, the reefs on the opposite side having 

 perished or never having existed. 



Submerged and Dead Reefs, — In the second sec- 

 tion of the first chapter, I have shown that there 

 sometimes exist in the neighbourhood of atolls, deeply 

 submerged banks with level surfaces; that there are 

 others, less deeply but yet wholly submerged, having 

 all the characters of a perfect atoll, but consisting 

 merely of dead coral-rock ; that there are barrier-reefs 

 and atolls with only a portion of the reef, generally 

 on the leeward side, submerged ; and that such 

 portions either retain their perfect outline, or appear 

 to be more or less completely effaced, their former 

 place being marked only by a bank, conforming in 

 general outline with that part of the reef which remains 

 perfect. These several cases are, I believe, intimately 

 related, and can all be explained by the same agency of 

 subsidence. 



We see that in those parts of the ocean where 

 coral-reefs are most abundant, one island is fringed and 

 another neighbouring one is not fringed, and that in 

 the same archipelago, all the reefs are more perfect 

 in one part than in another, — for instance, in the 

 southern compared with the northern half of the 

 Maldiva Archipelago, and likewise on the outer as 

 compared with the inner coasts of the double row of 

 atolls in this same archipelago. The existence of the 

 innumerable polypifers forming a reef, depends on 



