My dear Gray

I have directed a copy of my Book (as yet only an abstract) on the Origin of species to be sent you.—¹ I know how you are pressed for time; but if you can read it, I shall be infinitely gratified. From its condensed state it is indispensable to read it all straight through. If ever you do read it, & can screw out time to send me (as I value your opinion so highly) however short a note, telling me what you think its weakest & best parts, I should be extremely grateful. As you are not a geologist you will excuse my conceit in telling you that Lyell highly approves of the two geological chapters; & thinks that on the Imperfection of the Geological Record not exaggerated.² He is nearly a convert to my views.—

I have been so hard worked & my health so bad that I have not yet read your Japan Flora;³ but I will hereafter borrow Hooker’s copy. Hooker sent me a few pages in which you propound a doctrine of migration into America like that, which I sent you last summer in a letter.⁴ Dana is of course a far better authority than I am; but his arguments have by no means convinced me in regard to the warm period subsequent to the Glacial period.⁵ I daresay I may be wrong, but I rather doubt whether his & your view will explain facts of distribution so well as my view of migration during the certainly warmer period anteriorly to the Glacial period.⁶ Anyhow on my heteredox doctrine of modification your view does not bear on the representative species in the middle U. States. I thought of your doctrine several years ago, & consulted Lyell, but rejected it as less safe than the warm period anteriorly to Glacial Period. There seemed to me some little confusion about your fossil Elephants: the species in N. & S. States, I believe, are distinct according to Falconer.⁷ The northern one, anyhow, can hardly be adduced as evidence of warmer climate. But it is foolish in me to write on; for I am writing only after one hasty read, several months ago.—

Your Japan work must have been extremely interesting.

Farewell, with every good wish, especially for a little spare time for you

Pray believe me | Dear Gray | Yours very sincerely | Charles Darwin

P.S. I suppose that you have not succeeded in getting me any information on correlation of complexion in Europeans & tendency to yellow or other Tropical Fevers.—⁸

Let me add that I fully admit that there are very many difficulties not satisfactorily explained by my theory of descent with modification, but I cannot possibly believe that a false theory would explain so many classes of facts, as I think it certainly does explain.— On these grounds I drop my anchor & believe that the difficulties will slowly disappear.—