described by Mr Daricin. 47 



Thirdly, What seems to us the most serious objection to the 

 theory, remains to be stated. On the outside of coral reefs 

 very highly inclined, no bottom is sometimes found with a Ime 

 of 2U00 or 3000 feet, and this is by no means a rare case. 

 It follows that the reef ought to have this thickness ; and Mr 

 Darwin's diagrams, pages 48 and 98, shew that he understood 

 it so. Now, if such masses of coral exist under the sea, they 

 ought somewhere to be found on terra firma ; for there is evi- 

 dence that all the lands yet visited by geologists have been at 

 one time submerged. But neither in the great volcamc chain, 

 extending from Sumatra to Japan, nor in the West Indies, 

 nor in any other region yet explored, has a bed or formation 

 of coral, even 500 feet thick, been discovered, so far as we know. 

 We state this objection, not as conclusive against the theory, 

 but as one deserving the able and ingenious author^s consider- 

 ation. 



Bemarks on the preceding paper, in a Letter from Charles 

 Darwin, Esq., to Mr Maclaren. 



Down near Broomley, Kent, 

 Dear Sir —I have been so much pleased with the very clear, and, at the 

 same time, in many points quite original manner in ^hich you have stated 

 and explained my views, that I cannot refrain from troubling you with my 

 thanks. Your third objection appears to me much the most, indeed the 

 only, formidable one, wl.ich has hitherto occurred to me. I fear I shall 

 be tempted to reply to it at great length, but perhaps sometime you will 

 find leisure to read my attempted vindication. With respect to the first 

 objection, I can hardly admit that we know enough of the laws of ele- 

 vation and subsidence to argue against the theory, because the areas of 

 diff-erent movements are not more distinct. Some have been startled at 

 my view on directly the reverse grounds to your objection, viz. that, 

 according to their notions of probability, the areas of the same movements 

 were too large and uniform. With respect to your second objection, all 

 those who believe that exceedingly slow and gradual elevations are the 

 order of nature, must admit a great amount of contemporaneous denuda- 

 tion, which would tend to annihilate the characteristic form of the fnng- 

 ing-reefs during their upheaval, and leave merely a coating on the upraised 

 land of coral-rock either thicker or thinner, according to the original thick- 

 ness, rate of growth of the reef at each successive level, and the rate of 

 elevation ; indeed I am surprised that there exists even one case, viz. at 

 Mauritius, where the peculiar moat-like structure of a mere fringmg-reef 

 has been partially preserved on dry land. 



Your third criticism strikes me as a very weighty and perplexing one. 



