gain hold that a portion is pre-glacial
and the rest glacial and post-glacial. Those who have studied the
subject most closely feel convinced that the south-western or Lusitanian
fauna, and also the flora, must have arrived before the Glacial period
and survived the latter in these Islands. It seems reasonable to
suppose, therefore, that the climate cannot have been very severe during
the so-called Ice-Age. This Lusitanian fauna must be looked upon as the
oldest portion of the British fauna. The Alpine and Oriental migrations
arrived next. After these came the Arctic, and finally the Eastern or
Siberian. As the fossil evidence is most complete with regard to the
last, we are able to determine with precision not only the direction
whence this migration came, but approximately its geological age. It
arrived in Germany from the east after the deposition of the lower
boulder-clay. Since the boulder-clay is looked upon as a glacial
deposit, the Siberian migration reached Central Europe after the first
portion of the Glacial period had passed. In England it makes its first
appearance in the Forest-Bed, which would therefore correspond to the
"Loess" formation of Central Europe. All the other migrations are older
than the Siberian. They must therefore have come to Great Britain during
the earlier part of the Glacial period or before it.

The chapter concludes with a short statement on the physical geography
of the British Islands during the time when these migrations entered
them. That there existed a continuous coast-line between France and
Ireland is proved by the occurrence of a considerable number of
identical shore species, whilst the former existence of a freshwater
lake on the site of the present Irish Sea is indicated by the
distribution of some freshwater fishes.

CHAPTER IV.

THE ARCTIC FAUNA.

The lands lying within the Polar Circle are inhabited by an assemblage
of animals and plants, many of which are peculiar to those regions. They
are mostly adapted to the abnormal conditions of life prevailing in the
high latitudes of our globe--the long, dark winters, and the short
summers of one long day. Though the numbers of species and of
individuals are few, there is a keen struggle for existence in those
regions. The prevailing colour of the ground is white, and since a
resemblance in the colour of an animal to the ground it lives on acts as
a protection to weak ones, and also enables Carnivores to approach t