distances from where they grew. The probability, however, is in
favour of most of them having lived where their remains are now found.
Now, it is a remarkable fact, that the single instance in Europe of a
deposit of Arctic plants having been found far removed from the maximum
extension of the northern ice-sheet is the one quoted above, viz., at
Bovey Tracey, in Devonshire. Even up to recent times Arctic plants may
have persisted at Bovey Tracey just as they do in Galway under the
influence of a mild coast climate. Similar circumstances may have led to
their survival along the shores of the sea which deposited the North
European boulder-clay, while they moved northward from the Alps along
with the glaciers, which always supplied them with an abundance of
moisture. Alpine plants probably became exterminated in the plain of
Central Europe at a much earlier period.

SUMMARY OF CHAPTER V.

What has been spoken of in the earlier parts of this book as the eastern
migration, refers in a general way to the animals which have come to
England from the east. But these are by no means natives of one country
alone. We can trace a number of the British mammals to a Siberian
origin, and also some birds; among many of the lower vertebrates and
invertebrates, however, there are few species which have reached us from
Siberia. They may have had their original homes in the Alps, in Eastern
Europe, or in Central and Southern Asia, and have joined in their
westward course the later, more quickly travelling mammals. Many
instances are given from all the more important groups of animals to
show how we may proceed in approximately identifying the home of a
species.

The periodical invasion into our continent of Pallas's Sandgrouse and
other birds, suggests an explanation as to the cause of the great
westward migration in former times of the Siberian mammals. Since a
considerable amount of fossil evidence is available to show the path of
migration pursued by these mammals, other important problems, such as
the time of their arrival in Europe and the geographical conditions
surrounding them, may perhaps be approximately ascertained, and thus
throw much light on the general features of the European fauna. It has
been proved by Professor Nehring that the Siberian mammals arrived in
Eastern Europe after the deposition of the lower continental
boulder-clay. He believes that the climate of Germany at that time had
ameliorated so far, after the max