in to make
their appearance.

After these come the Tertiary periods: the Eocene first, where the
landscape is already broken up by hills and mountains, clothed with
a varied vegetation of comparatively modern character. Lily-pads are
floating on the stream which makes the central part of the picture;
large herds of the Palaeotherium, the ancient Pachyderm, reconstructed
with such accuracy by Cuvier, are feeding along its banks; and a tall
bird of the Heron or Pelican kind stands watching by the water's edge.
In the Miocene the vegetation looks still more familiar, though the
Elephants roaming about in regions of the Temperate Zone, and the huge
Salamanders crawling out of the water, remind us that we are still far
removed from present times. Lastly, we have the ice period, with the
glaciers coming down to the borders of a river where large troops of
Buffalo are drinking, while on the shore some Bears are feasting on the
remains of a huge carcass.

It is, however, with the Carboniferous age that we have to do at
present, and I will not anticipate the coming chapters of my story by
dwelling now on the aspect of the later periods. To return, then, to the
period of the coal, it would seem that extensive freshets frequently
overflowed the marshes, and that even after many successive forests
had sprung up and decayed upon their soil, they were still subject to
submergence by heavy floods. These freshets, at certain intervals,
are not difficult to understand, when we remember, that, beside the
occasional influx of violent rains, the earth was constantly undergoing
changes of level, and that a subsidence or upheaval in the neighborhood
would disturb the equilibrium of the waters, causing them to overflow
and pour over the surface of the country, thus inundating the marshes
anew.

That such was the case we can hardly doubt, after the facts revealed
by recent investigations of the Carboniferous deposits. In some of the
deeper coal-beds there is a regular alternation between layers of coal
and layers of sand or clay; in certain localities, as many as ten,
twelve, and even fifteen coal-beds have been found alternating with as
many deposits of clay or mud or sand; and in some instances, where the
trunks of the trees are hollow and have been left standing erect, they
are filled to the brim, or to the height of the next layer of deposits,
with the materials that have been swept over them. Upon this set of
deposits comes a new bed