d 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.

This summary account of the levelling process which went on during the
Triassic and Jurassic will prepare us to expect a return of warm climate
and luxurious life, and this the record abundantly evinces. The enormous
expansion of the