pened up a
passage for the Siberian fauna, we have in this very fact also an
explanation of the extraordinarily large exodus of Asiatic mammals,
because the great reduction of the marine area in Northern Europe would
have had an important influence in lowering the temperature in Asia.
Only a sudden change of climate in Siberia could have brought about the
migration of the vast hordes of Asiatic mammals whose remains we find in
Central and Western Europe in deposits of that period.

Throughout this work we are made acquainted with facts which bear out
the view that the climate during the greater part of the Glacial period
was mild rather than intensely arctic in Europe. That a huge ice-sheet
could have covered Northern Europe under such conditions appears to me
very doubtful. No one can deny, however, that glaciers must have existed
during the Glacial period in all the mountainous regions of Central and
Northern Europe, though their existence is not incompatible with a mild
climate. Tree-ferns and other tropical vegetation grow at the foot of
glaciers in New Zealand. We need not even go so far afield, for in
Switzerland grapes ripen and an abundant fauna and flora thrive in close
proximity to some of the well-known glaciers.

One matter of importance still remains to be considered before
concluding this chapter, viz., the fauna contained in the English
geological deposit known as the "Forest-Bed." This interesting deposit
is exposed at the base of a range of cliffs on the coast of Norfolk. It
is composed of beds of estuarine and marine origin. The tree-stumps
formerly believed to be the remains of trees _in situ_ have, after more
careful examination, proved to be in all cases drifted specimens. A
portion of the "Forest-Bed" no doubt was laid down in close proximity to
a large river, and subject to being periodically flooded by it. It is
not absolutely certain, therefore, that all the mammals whose remains
occur in this deposit lived in England or whether only on the banks of
the river farther south. Nevertheless, we may take for granted that some
of them did. England was at the time connected with France and Belgium,
and for our purpose it matters little whether they had crossed the
Channel or inhabited those parts of the Continent through which the
great river flowed which sent its alluvial detritus as far as the plains
of Norfolk. All we have to remember is that certain mammals, which
appear to have originated in Sibe