My dear Sir

I am very much obliged to you for having taken the trouble to answer my query so fully.¹ I can now be at rest, for from what you say & from what little I remember Forbes said, my point is unanswerable. The case of Terebratula is to the point, as far as it goes, and is negative.— I have already attempted to get a solution through geographical distribution by D^r. Hooker’s means, & he finds that same genera which have very variable species in Europe, have other very variable species elsewhere. This seems the general rule, but with some few exceptions.— I see from the several reasons which you assign, that there is no hope of comparing the same genus at two different periods, & seeing whether the tendency to vary is greater at one period in such genus than at another period.— The variability of certain genera or groups of species strikes me as a very odd fact.—

I shall have no points, as far as I can remember, to suggest for your reconsideration, but only some on which I shall have to beg for a little further information.—² However I feel inclined very much to dispute your doctrine of islands being generally ancient in comparison, I presume, with continents. I imagine you think that islands are generally remnants of old continents, a doctrine which I feel strongly disposed to doubt— I believe them generally rising points, you, it seems, think them sinking points—³

With many thanks | Yours very sincerely | C. Darwin