ccurred a phase of extreme mildness immediately after the
Glacial period, and that it was during that time that the Lusitanian
fauna and flora became established in the British Islands. To this
Professor James Geikie replies (_b_, p. 169), "there are few points we
can be more sure of than this, that since the close of the Glacial
epoch--since the deposition of the clays with Arctic shells and the
Saxicava sands--there have been no great oscillations, but only a
gradual amelioration of climate. It is quite impossible to believe that
any warm period could have intervened between the last Arctic and the
present temperate conditions without leaving some notable evidence in
the superficial deposits of Scotland, Scandinavia, and North America."
Thus it appears that on the whole the assumption that the Lusitanian
fauna and flora are very ancient and pre-glacial is also supported on
geological evidence.

[Illustration: Fig. 5.--Map of Europe, with arrows indicating
approximately the course taken by the different streams of migration
towards the British Islands.]

The course of events in the origin of the British fauna might have been
therefore somewhat as follows:--In early Tertiary times, when the
climate all over Western Europe was moist and semi-tropical, a migration
proceeded northward from the south-western corner of Europe. This was
strengthened by Oriental migrants which had moved westward along the
Mediterranean basin (Fig. 5, No. 1). Owing to geographical changes
supervening, the Alpine fauna (No. 2) was then enabled to colonise the
British Islands, and subsequently another migration had begun to come in
from the south-east (No. 3). The climate had meanwhile gradually become
more temperate and drier. About the same time, or even earlier, an
Arctic migration commenced to pass southward (No. 4), and finally the
Siberian animals (No. 5) poured into our continent. The arrows in the
map indicate the directions followed by the different migrants as they
travelled to the British Islands. The arrows are not meant to represent
the whole nor the full extent of the migrations from any particular
centre, but only in so far as they affect our islands. Moreover, it
would be impossible to indicate on one map the geographical conditions
which obtained during the several migrations. It must be remembered that
during the time which elapsed while they passed into the British
Islands, these were joined in the north to Scandinavia and in