DARWIN. 69 



direction would be due to his intercourse with Dr. Grant 

 at Edinburgh, whose celebrated paper on the fresh-water 

 sponge concludes with a declaration of his belief that 

 species are descended from other species, and that they be- 

 come improved in the course of modification. But previous 

 to the occurrences of his voyage, we can find no stronger 

 influence tending to make Darwin an evolutionist, than 

 Lyell's " Principles of Geology," which, by showing con- 

 stant and gradual change as the law of the world's history 

 now as in past periods, gave emphasis and point to all 

 observations of change and succession in the living world. 

 Indeed, in June, 1836, before Darwin's voyage was over, 

 Lyell writes to Sir John Herschel : " In regard to the 

 origination of new species, I am very glad to find that 

 you think it probable that it may be carried on through 

 the intervention of intermediate causes. I left this rather 

 to be inferred, not thinking it worth while to offend a certain 

 class of persons by embodying in words what would only 

 be a speculation. But the German critics have attacked 

 me vigorously, saying, that by the impugning of the doc- 

 trine of spontaneous generation, and substituting nothing 

 in its place, I have left them nothing but the direct and 

 miraculous intervention of the First Cause, as often as a 

 new species is introduced, and hence I have overthrown 

 my own doctrine of revolutions carried on by a regular 

 system of secondary causes. . . . When I first came to 

 the notion, which I never saw expressed elsewhere, though 

 I have no doubt it had all been thought out before, of a 

 succession of extinction of species, and creation of new 

 ones going on perpetually now, and through an indefinite 

 period of the past, and to continue for ages to come, all 



