1856.] CLASSIFICATION. 439 



subsidence of 20,000 or 30,000 feet ; it is only probability, con- 

 sidering such evidence as we have independently of distribu- 

 tion. I have not yet worked out in full detail the distribution 

 of mammalia, both identical and allied, with respect to the one 

 element of depth of the sea ; but as far as I have gone, the 

 results are to me surprisingly accordant with my very most 

 troublesome belief in not such great geographical changes as 

 you believe ; and in mammalia we certainly know more of 

 means of distribution than in any other class. Nothing is so 

 vexatious to me, as so constantly finding myself drawing 

 different conclusions from better judges than myself, from the 

 same facts. 



I fancy I have lately removed many (not geographical) 

 great difficulties opposed to my notions, but God knows it 

 may be all hallucination. 



Please return Lyell's letters. 



What a capital letter of Lyell's that to you is, and what a 

 wonderful man he is. I differ from him greatly in thinking 

 that those who believe that species are not fixed will multiply 

 specific names : I know in my own case my most frequent 

 source of doubt was whether others would not think this or 

 that was a God-created Barnacle, and surely deserved a name. 

 Otherwise I should only have thought whether the amount 

 of difference and permanence was sufficient to justify a name : 

 I am, also, surprised at his thinking it immaterial whether 

 species are absolute or not : whenever it is proved that all 

 species are produced by generation, by laws of change, what 

 good evidence we shall have of the gaps in formations. And 

 what a science Natural History will be, when we are in our 

 graves, when all the laws of change are thought one of the 

 most important parts of Natural History. 



I cannot conceive why Lyell thinks such notions as mine 

 or of ' Vestiges/ will invalidate specific centres. But I must 

 not run on and take up your time. My MS. will not, I fear, 

 be copied before you go abroad. With hearty thanks. 



Ever yours, 



C. Darwin. 



