ria, and of which we have some
evidence that they crossed Central Europe in their westward course, had
now reached the great river just alluded to, which some geologists
believe to have been the Rhine.

I have had occasion to refer to a number of British mammals (p.
202)--some of which are now extinct--which I believe to have migrated
across the plains of continental Europe direct from Siberia. There were
twenty-six species of these Siberian mammals; and no less than ten of
these occur in the Forest-Bed. None appear in any older British deposit.
It is perfectly clear, therefore, that the Forest-Bed must have been
laid down after their immigration into Europe. They probably wandered to
Western Europe very soon after crossing the eastern boundaries of our
continent; the deposits in which they are found are therefore
contemporaneous. But we have learned above (p. 208), that the beds in
Eastern Europe in which the Siberian mammal-remains are found are more
recent than the lower boulder-clay. As already stated, the Forest-Bed
must also be more recent than the lower continental boulder-clay, and
should be included in the pleistocene series.

That the Forest-Bed is an inter-glacial deposit has been urged long ago
by various writers. Professor Geikie regards it as stratigraphically
contemporaneous with the peat and freshwater beds below the lower
diluvium of Western and Middle Germany, and as having been laid down
during the first Inter-glacial Epoch of the great Ice-Age. The fact
that no boulder-clay underlies the Forest-Bed seems rather a strong
argument against the view of its being an inter-glacial deposit. It lies
directly on what is known as the Newer Pliocene Crags. If the Forest-Bed
is included in the pleistocene series, as I suggested it should, the
crags, or a portion of them, would therefore be equivalent as regards
time of deposition to the lower continental boulder-clay. And again, if
the lower continental boulder-clay is contemporaneous with the Newer
Crags, the latter should also be classed with the pleistocene strata. I
can scarcely hope that geologists will be ready to admit such a sweeping
change of nomenclature without a protest. I venture, therefore, to
explain more fully my reasons for adhering to these unorthodox views.

Let us look once more at the map which I constructed (Fig. 12, p. 156)
to elucidate the migration of the Arctic terrestrial species to the
British Islands. It will be noticed that one co