My dear Gray,
Your note of July 27th has just reached me in the Isle of Wight. It is a real and great pleasure to me to write to you about my notions; and even if it were not so, I should be a most ungrateful dog, after all the invaluable assistance you have rendered me, if I did not do anything which you asked.
I have discussed in my long MS. the later changes of climate and the effect on migration, and I will here give you an ABSTRACT of an ABSTRACT (which latter I am preparing of my whole work for the Linnean Society). I cannot give you facts, and I must write dogmatically, though I do not feel so on any point. I may just mention, in order that you may believe that I have SOME foundation for my views, that Hooker has read my MS., and though he at first demurred to my main point, he has since told me that further reflection and new facts have made him a convert.
In the older, or perhaps newer, Pliocene age (a little BEFORE the Glacial epoch) the temperature was higher; of this there can be