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 long enough to admit the formation of great beds of peat
in some portions. Peat is formed by the decomposition of
vegetable growth. Its growth is in all cases slow, depending
entirely upon local circumstances. European scholars who have
made peat formation a special study assure us that to form such