nown as
"discontinuous distribution," which zoologists are agreed to regard as
a sign of antiquity. Thus _Geomalacus maculosus_, the Kerry Slug, is in
the British Islands confined to South-western Ireland (see Fig. 19, p.
300), and on the Continent it is unknown north of North-western Spain.
The Millipede, _Polydesmus gallicus_, has a wider range in Ireland, and
is also known from France and the Azores. Two Earthworms of the Spanish
and Mediterranean region, viz., _Allolobophora veneta_ and _Georgii_,
have been discovered in Ireland, but are apparently unknown in England
or France; whilst the Weevil, _Otiorrhynchus auropunctatus_, does not
occur north of the Auvergne Mountains in France except in Ireland. A
very large number of instances might be mentioned of species found in
South-western Europe, France, the South-west of England and Ireland.
Enough, however, has been said to show the nature of the fauna, and
there is, as Forbes has pointed out, a corresponding flora.

A great number of the species belonging to the South-western British
element seem to have originated in South-western Europe, or at any rate
to have spread over our continent from that part. Their home lay
therefore probably in a warm, damp climate, and it seems a reasonable
inference to suppose that they spread north at a time when the
temperature over the British Islands was much higher than what it is
now. Any one familiar with our Bristle fern, or Killarney fern, as it is
called in Ireland (_Trichomanes radicans_), will readily admit that it
must have come to us at such an epoch. It at once suggests some shady
waterfall in a tropical forest, and indeed the home of the genus is
South America. It is one of those plants which have evidently migrated
to us from South-western Europe, a mere remnant of a once luxuriant
flora.

Sir Archibald Geikie tells us (p. 837), and in the main every one agrees
with him, that at the beginning of the Tertiary era in which we now
live, the climate was of a tropical and subtropical character in Europe.
Gradually it became more temperate, and eventually it passed into a
phase of extreme cold, but since that time the cold has again gradually
diminished. It is quite evident, therefore, that from a purely
geological point of view our south-western flora must have migrated
northward before the cold came on, and survived in sheltered localities
under the influence of the mild coast climate. Some, however, suppose
that there o