I hope that you will permit me to thank you for sending me a copy of your paper in "The Geologist" (124/1. In a letter to Hooker (April 23rd?, 1861) Darwin refers to Hutton's review as "very original," and adds that Hutton is "one of the very few who see that the change of species cannot be directly proved..." ("Life and Letters," II., page 362). The review appeared in "The Geologist" (afterwards known as "The Geological Magazine") for 1861, pages 132-6 and 183-8. A letter on "Difficulties of Darwinism" is published in the same volume of "The Geologist," page 286.), and at the same time to express my opinion that you have done the subject a real service by the highly original, striking, and condensed manner with which you have put the case. I am actually weary of telling people that I do not pretend to adduce direct evidence of one species changing into another, but that I believe that this view in the main is correct, because so many phenomena can be thus grouped together and explained. But it is generally of no use; I cannot make persons see this. I generally throw in their teeth the universally admitted theory of the undulation of light,--neither the undulation nor the very existence of ether being proved, yet admitted because the view explains so much. You are one of the very few who have seen this, and have now put it most forcibly and clearly. I am much pleased to see how carefully you have read my book, and, what is far more important, reflected on so many points with an independent spirit. As I am deeply interested in the subject (and I hope not exclusively under a personal point of view) I could not resist venturing to thank you for the right good service which you have done. I need hardly say that this note requires no answer. LETTER 125. TO J.D. HOOKER. (125/1. Parts of this letter are published in "Life and Letters," II., page 362.) Down, [April] 23rd, [1861].