ceros, hyenas,
cave-bear, and cave-lion.<34>

In the formation of these gravel beds, ice has undoubtedly played quite
an important part. Bowlders that could have got there only by the aid
of ice, are found in several localities. Evidence gathered from a great
many different sources all establish the fact that these gravels date
as far back as the close of the Glacial Age at least, and there are some
reasons for supposing them to be interglacial.

We can easily see that the melting away of the immense glaciers that we
have been describing would produce vast floods in the rivers, and it is
perhaps owing to the presence of such swollen rivers that are due the
great beds of surface soil, called loam or loess, found in all the river
valleys of France and Germany.<35> These deposits frequently overlie the
gravel beds. They are then of a later date than the beds in which
are found such convincing proofs of the presence of man, and if they
themselves date from the close of the Glacial Age, it is no longer a
question whether the gravel beds themselves belong to that age. Thus we
see that we can no longer escape the conclusions of Boucher DePerthes.
The discovery of rudely worked flints in the drift of the Somme River
thus establishes the fact that some time during the Glacial Age, man in
a Paleolithic state lived in France.

Geological terms convey to us no definite ideas as to the lapse of time,
and we have an instinctive desire to substitute for them some term of
years. In most cases this is impossible, as we have no means to measure
the flight of past time, nor are we yet prepared to discuss the question
of time, since to do so we must learn a great deal more about the cause
of the Glacial Age. We might, however, cite statements which can not
fail to impress us with the fact that a great extent of time has passed.

In the case of the river Somme we have a valley in some places a mile or
more in width, and about two hundred feet in depth. This has mostly been
excavated in chalk rock. Taking our present large rivers as a basis, it
would require from one to two hundred thousand years for the Somme to
perform this work.<36> It will not do, however, to take the present
action of our rivers as a guide, since we have every reason to suppose
this work went forward much more rapidly in past times. But we can not
escape the conclusion that it demands a very long time indeed to explain
it. The valley has remained in its present shape