ontinued, uninterruptedly,
for very long periods.

The study of these migrations has convinced me that, though climate was
a powerful factor in the evolution or history of the European fauna, the
geographical changes which took place on our continent in later Tertiary
times exerted a yet stronger influence. The principal climatic
disturbance is generally supposed to have been the so-called "Ice Age."
So firmly rooted is the conviction, among naturalists of the present
day, of the enormous destruction which this period produced on our
European fauna, so that all animal life practically disappeared from
large areas of our continent, that it is desirable that we should now
shortly review the history of that remarkable period in order to
ascertain in how far these views are corroborated by facts. Frequent
reference, moreover, will be made throughout this work to the theories
connected with the Glacial period.

It has been stated by an eminent geologist that during part of the
Glacial period the climate was such that neither plants nor animals
could have existed in the British Islands. If that had been so, it is
evident that very few organisms could have even survived in France,
though a number of Arctic species might have dragged on an existence in
Southern Europe. At any rate, on the return of more genial conditions,
the Arctic species would undoubtedly have been the first to gain
admission to the British Islands, to re-people the arid wastes. Our
supposition that the Lusitanian element in the British fauna is the
oldest would therefore be wrong. From early Tertiary times onward, the
climate of Europe, which was then semi-tropical, gradually became more
and more temperate; until finally the Ice Age or Glacial period arrived,
during which, according to Professor J. Geikie--one of our highest
authorities on this subject--a great part of Northern Europe became
practically uninhabitable owing to the severity of the climate.

To enable us to judge better of the true value of the many hypotheses
which have been advanced to account for this supposed extraordinary fall
of temperature during the "Ice Age," we must compare the views of other
authorities with the one just quoted. I do not propose to discuss the
causes which have led to the production of the Glacial period--those
interested in these questions should consult the writings of Dr. Croll,
Professor J. Geikie, Professor Bonney, Mr. Falsan, and others--but
merely to give