Peter's Road, Croydon. November 8, 1880._
My dear Darwin,--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
waters 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.
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