To Asa Gray 11 November 
Down Bromley Kent [Ilkley]
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.—
Sends copy of Origin for comments.
Does not feel AG’s views of migration after the last glaciation explain distribution in U. S. as well as CD’s view of migration prior to glaciation.
Please cite as
Darwin Correspondence Project, “Letter no. 2520,” accessed on 18 January 2017, http://www.darwinproject.ac.uk/DCP-LETT-2520