The regions of green vegetation shrank before the
oncoming ice, the animals retreated south, or developed Arctic
features. Europe and America were ushering in the great Ice-Age,
which was to bury five or six million square miles of their
territory under a thick mantle of ice.
Such is the general outline of the story of the Tertiary Era. We
approach the study of its types of life and their remarkable
development more intelligently when we have first given careful
attention to this extraordinary series of physical changes. Short
as the Era is, compared with its predecessors, it is even more
eventful and stimulating than they, and closes with what
Professor Chamberlin calls "the greatest deformative movements in
post-Cambrian history." In the main it has, from the evolutionary
point of view, the same significant character as the two
preceding eras. Its middle portion is an age of expansion,
indulgence, exuberance, in which myriads of varied forms are
thrown upon the scene, its later part is an age of contraction,
of annihilation, of drastic test, in which the more effectively
organised will be chosen from the myriads of types. Once more
nature has engendered a vast brood, and is about to select some
of her offspring to people the modern world.
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