In shells, I hope hereafter to get much light on this question through fossils.

If you can help me, I should be very much obliged: indeed, all your letters are most useful to me.
MONDAY:--Now for your first long letter, and to me quite as interesting as long.

Several things are quite new to me in it--viz., for one, your belief that there are more extra-tropical than intra-tropical species.

I see that my argument from the Arctic regions is false, and I should not have tried to argue against you, had I not fancied that you thought that equability of climate was the direct cause of the creation of a greater or lesser number of species.

I see you call our climate equable; I should have thought it was the contrary.