e chronicle of life from the point of view of time or
antiquity, just as the Middle Ages of Europe are by no means the centre
of the chronicle of mankind, but its types of animals and plants are
singularly transitional between the extinct ancient and the actual
modern types. Life has been lifted to a higher level by the Permian
revolution. Then, for some millions of years, the sterner process of
selection relaxes, the warm bosom of the earth swarms again with a
teeming and varied population, and a rich material is provided for the
next great application of drastic selective agencies. To a poet it might
seem that nature indulges each succeeding and imperfect type of living
thing with a golden age before it is dismissed to make place for the
higher.

The Mesozoic opens in the middle of the great revolution described in
the last chapter. Its first section, the Triassic period, is at first a
mere continuation of the Permian. A few hundred species of animals and
hardy plants are scattered over a relatively bleak and inhospitable
globe. Then the land begins to sink once more. The seas spread in great
arms over the revelled continents, the plant world rejoices in the
increasing warmth and moisture, and the animals increase in number and
variety. We pass into the Jurassic period under conditions of great
geniality. Warm seas are found as far north and south as our present
polar regions, and the low-lying fertile lands are covered again with
rich, if less gigantic, forests, in which hordes of stupendous animals
find ample nourishment. The mammal and the bird are already on the
stage, but their warm coats and warm blood offer no advantage in that
perennial summer, and they await in obscurity the end of the golden age
of the reptiles. At the end of the Jurassic the land begins to rise once
more. The warm, shallow seas drain off into the deep oceans, and the
moist, swampy lands are dried. The emergence continues throughout the
Cretaceous (Chalk) period. Chains of vast mountains rise slowly into the
air in many parts of the earth, and a new and comparatively rapid
change in the vegetation--comparable to that at the close of the
Carboniferous--announces the second great revolution. The Mesozoic
closes with the dismissal of the great reptiles and the plants on which
they fed, and the earth is prepared for its new monarchs, the flowering
plants, the birds, and the mammals.

How far this repeated levelling of the land after its repeate