o the solution of the
problem of the origin of European animals. We know that our British
species came to us by land--at least the bulk of them. But we want to
know what direction they came from, and at what time they arrived. When
Ireland became disconnected from Great Britain, and the latter from
Scandinavia and France, is another interesting problem. Professor Boyd
Dawkins has indicated to us a method of the special line of research to
meet such inquiries. "The absence," he says (_b_, p. xxix), "of the
beaver and the dormouse from Ireland must be due to the existence of
some barrier to their westward migration from the adjacent mainland, and
the fact that the Alpine hare is indigenous, while the common hare is
absent, implies that, so far as relates to the former animal, the
barrier did not exist."

Many members of the great Siberian invasion reached England, but Ireland
remained entirely free from these migrants. The assumption therefore
seems not unreasonable, that the latter country at the time of their
arrival was no longer joined to England. The great bulk of the Irish
fauna is composed of Lusitanian, Alpine, and Oriental immigrants, and
there is besides a distinctly Arctic or North American element. All
these, of course, must have established themselves in Ireland before
the Siberian fauna set foot in England, since it has been shown that a
continuous land-surface was necessary for their migration. Owing to the
perfect preservation of the remains of the Siberian migrants in recent
continental deposits, the history of that migration can be clearly
followed, and it is possible even to determine the date of its arrival
in England--in geological language at any rate. The time of the
colonisation of Ireland can be thus approximately fixed as having taken
place at a period prior to the arrival of the Siberian migrants in
England.

All those who have seriously studied the problems presented by our
British fauna--notably the late Professor Forbes, and more recently Mr.
Carpenter and myself--are agreed that the Lusitanian element is the
oldest, and that the newest is that which has come to us from the east.

The sequence of events in the British Islands was probably as
follows:--The first comers were the members of that fauna which issued
from South-western Europe; then came the Alpine, and at the same time
probably the Arctic and the Oriental; and finally the Eastern or
Siberian. The migrations of all but the last c