18411881] CORAL REEFS 195 



To C. Lyell. Letter 533 



[1842.] 



Considering the probability of subsidence in the middle 

 of the great oceans being very slow ; considering in how 

 many spaces, both large ones and small ones (within areas 

 favourable to the growth of corals), reefs are absent, which 

 shows that their presence is determined by peculiar con- 

 ditions ; considering the possible chance of subsidence being 

 more rapid than the upward growth of the reefs ; considering 

 that reefs not very rarely perish (as I cannot doubt) on part, 

 or round the whole, of some encircled islands and atolls : 

 considering these things, I admit as very improbable that 

 the polypifers should continue living on and above the same 

 reef during a subsidence of very many thousand feet ; and 

 therefore that they should form masses of enormous thickness, 

 say at most above 5,000 feet. 1 This admission, I believe, is 

 in no way fatal to the theory, though it is so to certain few 

 passages in my book. 



In the areas where the large groups of atolls stand, and 

 where likewise a few scattered atolls stand between such 

 groups, I always imagined that there must have been great 

 tracts of land, and that on such large tracts there must have 

 been mountains of immense altitudes. But not, it appears to 

 me, that one is only justified in supposing that groups of 

 islands stood there. There are (as I believe) many con- 

 siderable islands and groups of islands (Galapagos Islands, 

 Great Britain, Falkland Islands, Marianas, and, I believe, 

 Viti groups), and likewise the majority of single scattered 

 islands, all of which a subsidence between 4,000 and 5,000 

 feet would entirely submerge or would leave only one or two 

 summits above water, and hence they would produce either 

 groups of nothing but atolls, or of atolls with one or two 

 encircled islands. I am far from wishing to say that the 

 islands of the great oceans have not subsided, or may not 



1 "... As we know that some inorganic causes are highly injurious 

 to the growth of coral, it cannot be expected that during the round of 

 change to which earth, air, and water are exposed, the reef-building 

 polypifers should keep alive for perpetuity in any one place ; and still 

 less can this be expected during the progressive subsidences ... to 

 which by our theory these reefs and islands have been subjected, and 

 are liable" (The Structure and Distribution of Coral Reefs, p. 107 : 

 London, 1842). 



