EARLY NOTES ON SPECIES. 29 



vinced of this process when some conception as to 

 its causes had been offered to them ; Darwin took 

 the more logical course of first requiring evidence 

 that the process takes place, and then inquiring for 

 its causes. 



The first indication of these thoughts in any of 

 his published letters is in one to his cousin Fox 

 written in June, 1838, in which, after alluding to 

 some questions he had previously asked about the 

 crossing of animals, he says, " It is my prime hobby, 

 and I really think some day I shall be able to do 

 something in that most intricate subject — species 

 and varieties." 



He is rather more definite in a letter to Sir 

 Charles Lyell, written September 13th in the same 

 year : — 



*' I have lately been sadly tempted to be idle — that is, as far 

 as pure geology is concerned — by the delightful number of new 

 views which have been coming in thickly and steadily, — on the 

 classification and affinities and instincts of animals — bearing on 

 the question of species. Note-book after note-book has been 

 filled with facts which begin to group themselves clearly 

 under sub-laws." 



On February 16th, 1838, he was appointed 

 Secretary of the Geological Society, a position which 

 he retained until February 1st, 1841. During these 

 two years after the voyage he saw much of Sir 

 Charles Lyell, whose teachings had been of the 

 greatest help to him during the voyage, and whose 

 method of appealing to natural causes rather than 

 supernatural cataclysms undoubtedly had a most 



