places to
have been rapid and abrupt (Chamberlin); but in summary they amounted
to a vast revolution in the environment of animals and plants. The
low-lying, swampy, half-submerged continents reared themselves upward
from the sea-level, shook the marshes and lagoons from their face, and
drained the vast areas that had fostered the growth of the Coal-forests.
It is calculated (Chamberlin) that the shallow seas which had covered
twenty or thirty million square miles of our continental surfaces in the
early Carboniferous were reduced to about five million square miles in
the Permian. Geologists believe, in fact, that the area of exposed land
was probably greater than it is now.

This lifting and draining of so much land would of itself have a
profound influence on life-conditions, and then we must take account of
its indirect influence. The moisture of the earlier period was probably
due in the main to the large proportion of sea-surface and the absence
of high land to condense it. In both respects there is profound
alteration, and the atmosphere must have become very much drier. As this
vapour had been one of the atmosphere's chief elements for retaining
heat at the surface of the earth, the change will involve a great
lowering of temperature. The slanting of the raised land would aid this,
as, in speeding the rivers, it would promote the circulation of water.
Another effect would be to increase the circulation of the atmosphere.
The higher and colder lands would create currents of air that had not
been formed before. Lastly, the ocean currents would be profoundly
modified; but the effect of this is obscure, and may be disregarded for
the moment.

Here, therefore, we have a massive series of causes and effects, all
connected with the great emergence of the land, which throw a broad
light on the change in the face of the earth. We must add the lessening
of the carbon dioxide in the atmosphere. Quite apart from theories of
the early atmosphere, this process must have had a great influence,
and it is included by Professor Chamberlin among the causes of the
world-wide change. The rocks and forests of the Carboniferous period are
calculated to have absorbed two hundred times as much carbon as there is
in the whole of our atmosphere to-day. Where the carbon came from we may
leave open. The Planetesimalists look for its origin mainly in volcanic
eruptions, but, though there was much volcanic activity in the later
Carboniferou