LETTER 396. A.R. WALLACE TO CHARLES DARWIN.

(396/1. This letter is in reply to Mr. Darwin's criticisms on Mr.
Wallace's "Island Life," 1880.)

Pen-y-Bryn, St. Peter's Road, Croydon, November 8th, 1880.

Many thanks for your kind remarks and notes on my book. Several of the
latter will be of use to me if I have to prepare a second edition, which I
am not so sure of as you seem to be.

1. In your remark as to the doubtfulness of paucity of fossils being due
to coldness of water, I think you overlook that I am speaking only of water
in the latitude of the Alps, in Miocene and Eocene times, when icebergs and
glaciers temporarily descended into an otherwise warm sea; my theory being
that there was no Glacial epoch at that time, but merely a local and
temporary descent of the snow-line and glaciers owing to high excentricity
and winter in aphelion.

2. I cannot see the difficulty about the cessation of the Glacial period.

Between the Miocene and the Pleistocene periods geographical changes
occurred which rendered a true Glacial period possible with high
excentricity. When the high excentricity passed away the Glacial epoch
also passed away in the temperate zone; but it persists in the arctic zone,
where, during the Miocene, there were mild climates, and this is due to the
persistence of the changed geographical conditions. The present arctic
climate is itself a comparatively new and abnormal state of things, due to
geographical modification.