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Early Periods
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 repeated
upheavals is due to a real sinking of the crust we cannot as yet
determine. The geologist of our time is disposed to restrict
these mysterious rises and falls of the crust as much as
possible. A much more obvious and intelligible agency has to be
considered. The vast upheaval of nearly all parts of the land
during the Permian period would naturally lead to a far more
vigorous scouring of its surface by the rains and rivers. The
higher the land, the more effectively it would be worn down. The
cooler summits would condense the moisture, and the rains would
sweep more energetically down the slopes of the elevated
continents. There would thus be a natural process of levelling as
long as the land stood out high above the water-line, but it
seems probable that there was also a real sinking of the crust.
Such subsidences have been known within historic times.
By the end of the Triassic--a period of at least two million
years--the sea had reconquered a vast proportion of the territory
wrested from it in the Permian revolution. Most of Europe, west
of a line drawn from the tip of Norway to the Black Sea, was
under water--generally open sea in the south and centre, and
inland seas or lagoons in the west. The invasion of the sea
continued, and reached its climax, in the Jurassic period. The
greater part of Europe was converted into an archipelago. A small
continent stood out in the Baltic region. Large areas remained
above the sea-level in Austria, Germany, and France. Ireland,
Wales, and much of Scotland were intact, and it is probable that
a land bridge still connected the west of Europe with the east of
America. Europe generally was a large cluster of islands and
ridges, of various sizes, in a semi-tropical sea. Southern Asia
was similarly revelled, and it is probable that the seas
stretched, with little interruption, from the west of Europe to
the Pacific. The southern continent had deep wedges of the sea
driven into it. India, New Zealand, and Australia were
successively detached from it, and by the end of the Mesozoic it
was much as we find it to-day. The Arctic continent (north of
Europe) was flooded, and there was a great interior sea in the
western part of the North American continent.
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