...I think that I must have expressed myself badly about Humboldt. I
should have said that he was more remarkable for his astounding knowledge
than for originality. I have always looked at him as, in fact, the founder
of the geographical distribution of organisms. I thought that I had read
that extinct fossil plants belonging to Australian forms had lately been
found in Australia, and all such cases seem to me very interesting, as
bearing on development.

I have been so astonished at the apparently sudden coming in of the higher
phanerogams, that I have sometimes fancied that development might have
slowly gone on for an immense period in some isolated continent or large
island, perhaps near the South Pole. I poured out my idle thoughts in
writing, as if I had been talking with you.

No fact has so interested me for a heap of years as your case of the plants
on the equatorial mountains of Africa; and Wallace tells me that some one
(Baker?) has described analogous cases on the mountains of Madagascar
(398/1. See Letter 397, note.)...I think that you ought to allude to these
cases.

I most fully agree that no problem is more interesting than that of the
temperate forms in the southern hemisphere, common to the north. I
remember writing about this after Wallace's book appeared, and hoping that
you would take it up. The frequency with which the drainage from the land
passes through mountain-chains seems to indicate some general law--viz.,
the successive formation of cracks and lines of elevation between the
nearest ocean and the already upraised land; but that is too big a subject
for a note.

I doubt whether any insects can be shown with any probability to have been