LETTER 392. TO A.R. WALLACE.
Down, June 25th, 1876.

I have been able to read rather more quickly of late, and have finished
your book. I have not much to say. Your careful account of the temperate
parts of South America interested me much, and all the more from knowing
something of the country. I like also much the general remarks towards the
end of the volume on the land molluscs. Now for a few criticisms.

Page 122. (392/1. The pages refer to Volume II. of Wallace's
"Geographical Distribution.")--I am surprised at your saying that "during
the whole Tertiary period North America was zoologically far more strongly
contrasted with South America than it is now." But we know hardly anything
of the latter except during the Pliocene period; and then the mastodon,
horse, several great edentata, etc., etc., were common to the north and
south. If you are right, I erred greatly in my "Journal," where I insisted
on the former close connection between the two.

Page 252 and elsewhere.--I agree thoroughly with the general principle that
a great area with many competing forms is necessary for much and high
development; but do you not extend this principle too far--I should say
much too far, considering how often several species of the same genus have
been developed on very small islands?

Page 265.--You say that the Sittidae extend to Madagascar, but there is no
number in the tabular heading. [The number (4) was erroneously omitted.--
A.R.W.]