2. The assemblages of animals and plants
compositing that fauna and flora did not appear in the area they now inhabit
simultaneously, but at several distinct points in time. 3. Both the fauna
and flora of the British islands and seas are composed partly of species
which, either permanently or for a time, appeared in that area before the
glacial epoch; partly of such as inhabited it during that epoch; and in
great part of those which did not appear there until afterward, and whose
appearance on the earth was coeval with the elevation of the bed of the
glacial sea and the consequent climatal changes. 4. The greater part of
the terrestrial animals and flowering plants now inhabiting the British
islands are members of specific centers beyond their area, and have migrated
to it over continuous land before, during, or after the glacial epoch. 5.
The climatal conditions of the area under discussion, and north, east, and
west of it, were severer during the glacial epoch, when a great part of the
space now occupied by the British isles was under water, than they are now
or were before; but there is good reason to believe that, so far from those
conditions having continued severe, or having gradually diminished in
severity southward of Britain, the cold region of the glacial epoch came
directly into contact with a region of more southern and thermal character
than that in which the most southern beds of glacial drift are now to be met
with.
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