scontinuous range is generally a proof
of antiquity, continuous range is not always a sign of the opposite.
Some species, in fact, appear to be short-lived and disinclined to
spread, whilst others multiply rapidly even under a change of
temperature and climate, and are to be found almost everywhere. But even
if we supposed, with Mr. Carpenter, that these widely-ranging species
must have been confined during the Glacial period to the more southern
parts of England, the idea that they afterwards made their way
northwards along the eastern shore of the Irish Sea and then passed into
Ireland, does not appeal to me. Southern England was occupied at that
very same time by an assemblage of Siberian mammals. Mr. Carpenter
thinks these might have been kept out of Ireland by an arm of the sea
until the land-connection with North-western England had broken down.
But if an arm of the sea could keep out the Siberian mammals it would
also keep out the widely-spread British species of the general fauna. On
the other hand, I quite admit that my view of the survival in Ireland
of the pre-glacial fauna is somewhat difficult to accept, considering
that we have such undoubted evidence of a very extensive submergence.
The case of Isle of Man, quoted by Mr. Carpenter, can be met, I think,
by the supposition that it was connected with Cumberland until quite
recently, and quite independently of any connection between England and
Ireland; that the Isle of Man, in fact, was always a cape or peninsula
of the mainland, and only recently became separated by local subsidences
or by the action of the sea.

Part of the history of the British fauna will be referred to again in
the next chapter, which deals with the Arctic migration. We need not
therefore dwell any longer on this subject here. There is one matter,
however, which is of importance in connection with the geographical
conditions of the British Islands at the time when the greater portion
of our fauna arrived from abroad.

On page 60 will be found a map indicating the physical geography of that
part of the ancient continent on which what are now the British Islands
were situated. Only one large river has been marked on that map, namely,
that flowing out of a lake which occupied part of the Irish Sea. Another
probably discharged its waters into the Atlantic midway between France
and England, whilst the Thames may have been a tributary of the Rhine,
as it emptied itself into the sea near our