er found its way to the Isle of Man from the mainland on a
waning ice-sheet, he sees no reason why certain elements of the Irish
fauna should not have been similarly introduced.

It seems of no advantage to begin the discussion on the origin of the
British fauna by assuming the former existence of ice-bridges, and the
possibility of a migration across them of some of its members. If a
glacier connected Scotland and Ireland, the climate of both countries
(since they were highlands and acted as the feeders of the ice-sheet)
must have been uncomfortable to the majority of the British species.
What were the inducements that could have prompted those which had
braved the discomforts of Scotland to emigrate to Ireland at such a
time? What light does it throw on the origin of the Irish fauna as a
whole, to advance the extremely improbable hypothesis that certain
elements of it may have reached Ireland by an ice-bridge? If any
species came to that country in such an unusual manner, surely they must
have been Arctic or northern forms. But what about the southern species,
which form the bulk of the Irish fauna and also the flora? Even the
Arctic element of the British fauna, which probably includes, besides
the Reindeer, many hundreds of species, could not, I think, have
migrated to these islands on an ice-bridge. Indeed, I agree with most of
the writers who have dealt with the subject, in asserting that the
northern as well as all the other elements of our fauna utilised for
their migration the old land-bridges which connected these islands with
one another and with the Continent.

There is a greater diversity of opinion as to the age during which the
British fauna arrived in these islands. This is naturally a much more
complicated problem, but it is one which I am convinced will ultimately
be solved mainly by means of a study of the geographical distribution of
animals and plants. If we can settle the relative ages of the various
migrations, we thereby supply an important link in our attempt to
reconstruct the past geographical features of the British Islands. The
range of the British species will give us an idea of the nature of the
land-connections and their gradual changes in course of time. Geological
data are exceedingly valuable in these inquiries, but it is a fatal
mistake to build our geographical theories and the origin of the British
fauna as a whole entirely on the assumptions of a certain school of
geologists. Unfo