On the other hand, we have already, in discussing the Permian
glaciation, discovered two agencies which are very effective in
lowering the temperature of the earth. One is the rise of the
land; the other is the thinning of the atmosphere. These are
closely related agencies, and we found them acting in conjunction
to bring about the Permian Ice-Age. Do we find them at work in
the Pleistocene?
It is not disputed that there was a very considerable upheaval of
the land, especially in Europe and North America, at the end of
the Tertiary Era. Every mountain chain advanced, and our Alps,
Pyrenees, Himalaya, etc., attained, for the first time, their
present, or an even greater elevation. The most critical
geologists admit that Europe, as a whole, rose 4000 feet above
its earlier level. Such an elevation would be bound to involve a
great lowering of the temperature. The geniality of the Oligocene
period was due, like that of the earlier warm periods, to the
low-lying land and very extensive water-surface. These conditions
were revolutionised before the end of the Tertiary. Great
mountains towered into the snow-line, and vast areas were
elevated which had formerly been sea or swamp.
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