her step in the direction we are aiming at. Let us
suppose that the Siberian migration actually reached the British Islands
during the Forest-Bed period. Since the Siberian migration is the most
recent of those which entered the British Islands, the others must have
commenced their march before the Forest-Bed period. Now it was Professor
Boyd Dawkins who first indicated to us, as I have remarked before, the
method of research to be adopted in an attempt to determine the
geological age of the different migrations in so far as they affected
the British Islands. I may be excused, therefore, for again quoting the
following important passage in one of his works. "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." The Beaver, Dormouse, and
Common Hare are either Siberians or later migrants from elsewhere, and
there can be no doubt that at the Forest-Bed period Ireland was already,
or was just being, separated from England. All the southern species,
that is to say all the Lusitanian, Alpine, and Oriental forms occurring
in Ireland, must therefore be older than that period. I have advocated
similar views in a former essay on this subject. Mr. Carpenter recently
advanced some interesting and valuable criticisms on these views, which
we may examine a little more closely (p. 385). "While, then," he
remarks, "I find myself in almost complete agreement with Dr. Scharff
with regard to the older sections of our fauna, I think that those
widespread species which survived the Glacial period must have been
confined to the more southern parts of our area, and have only
subsequently spread northwards and westwards to Scotland and Ireland."
He suggests, in fact, that the widespread British species belong to a
younger or newer section of our fauna than the local ones. In many cases
this may be quite true, but we possess also a large number of common and
widely-spread forms which bear the impress of antiquity upon them. We
have the most positive proof of the antiquity of the very common small
circular Snail (_Helix rotundata_), since it was found in miocene
freshwater deposits near Bordeaux. Many other examples might be
mentioned to show that, though di