Except, to some extent,
the last of these points, there is no difference of opinion, and
therefore, from the evolutionary point of view, the Cretaceous
period merits the title of a revolution. All these things were
done before the Tertiary period opened.
Let us first consider the fundamental and physical aspect of this
revolution, the upheaval of the land. It began about the close of
the Jurassic period. Western and Central Europe emerged
considerably from the warm Jurassic sea, which lay on it and had
converted it into an archipelago. In North-western America also
there was an emergence of large areas of land, and the Sierra and
Cascade ranges of mountains were formed about the same time. For
reasons which will appear later we must note carefully this rise
of land at the very beginning of the Cretaceous period.
However, the sea recovered its lost territory, or compensation
for it, and the middle of the Cretaceous period witnessed a very
considerable extension of the waters over America, Europe, and
southern Asia. The thick familiar beds of chalk, which stretch
irregularly from Ireland to the Crimea, and from the south of
Sweden to the south of France, plainly tell of an overlying sea.
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