In some degree the cold penetrates
the whole earth. The rich forests shrink slowly into thin tracts
of scrubby, poverty-stricken vegetation. The loss of food and the
bleak and exacting conditions of the new earth annihilate
thousands of species of the older organisms, and the more
progressive types are moulded into fitness for the new
environment. It is a colossal application of natural selection,
and amongst its results are some of great moment.
In various recent works one reads that earlier geologists, led
astray by the nebular theory of the earth's origin, probably
erred very materially in regard to the climate of primordial
times, and that climate has varied less than used to be supposed.
It must not be thought that, in speaking of a "Permian
revolution," I am ignoring or defying this view of many
distinguished geologists. I am taking careful account of it.
There is no dispute, however, about the fact that the Permian age
witnessed an immense carnage of Carboniferous organisms, and a
very considerable modification of those organisms which survived
the catastrophe, and that the great agency in this annihilation
and transformation was cold.
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