the attempt. Only
at one point in all that distance did the ice wall sink low enough to
allow of its upper surface being seen from the mast-head. He describes
the upper surface as an immense plain shining like frosted silver,
and stretching away as far as eye could reach into the illimitable
distance.<9>

The foregoing makes plain to us one phase of the Glacial Age. Though it
may not be quite clear what this has to do with the antiquity of man,
yet we will see, in the sequel, that it has considerable. As to the
periods of mild climate that are thought by some to have broken up the
reign of cold, we do not feel that we can say any thing in addition to
what has been said in a former chapter.<10>

We might, however, say, that the sequences of mild and cold climate
are not as well made out in America as they seem to be in Europe; or at
least our geologists are more cautious as to accepting the evidence as
sufficient. And yet such evidences are not wanting: as in Europe,
at various places, are found layers of land surfaces with remains of
animals and plants, but both above and below such surface soil are found
beds of bowlder clay. These offer undeniable evidence that animals and
plants occupied the land during temperate inter-glacial epochs, preceded
and followed by an Arctic climate, and ice-sheets like those now
covering the interior of Greenland, and the Antarctic Continent.<11>

We have thus, though somewhat at length, gone over the evidence as
to the reality and severity of the Glacial Age. It was during the
continuance of such climate that Paleolithic man arrived in Europe,
though it was not perhaps until its close. We must not lose sight of the
fact that our principal object at present is to determine, if we can, a
date for either the beginning or ending of this extraordinary season of
cold, and thereby achieve an important step in determining the antiquity
of man.

A moment's consideration will show us that a period of cold sufficient
to produce over a large portion of the Northern Hemisphere the
results we have just set forth must have a cause that is strange
and far-reaching. It can not be some local cause, affecting but one
continent, since the effect produced is observed as well in Europe as in
America.

Every year we pass through considerable changes in climate. The four
seasons of the year seem to be but an annual repetition, on a very small
scale of course, of the great changes in the climate of the ear