es living in any
part of it adapted to the consequences resulting from more moisture. In
this case therefore, and still more (as we have seen) during the
production of new stations from the elevation of the land, an island
would be a far more fertile source, as far as we can judge, of new
specific forms than a continent. The new forms thus generated on an
island, we might expect, would occasionally be transported by accident,
or through long-continued geographical changes be enabled to emigrate
and thus become slowly diffused.

But if we look to the origin of a continent; almost every geologist will
admit that in most cases it will have first existed as separate islands
which gradually increased in size{409}; and therefore all that which has
been said concerning the probable changes of the forms tenanting a small
archipelago is applicable to a continent in its early state.
Furthermore, a geologist who reflects on the geological history of
Europe (the only region well known) will admit that it has been many
times depressed, raised and left stationary. During the sinking of a
continent and the probable generally accompanying changes of climate the
effect would be little, _except_ on the numerical proportions and in the
extinction (from the lessening of rivers, the drying of marshes and the
conversion of high-lands into low &c.) of some or of many of the
species. As soon however as the continent became divided into many
isolated portions or islands, preventing free immigration from one part
to another, the effect of climatic and other changes on the species
would be greater. But let the now broken continent, forming isolated
islands, begin to rise and new stations thus to be formed, exactly as in
the first case of the upheaved volcanic islet, and we shall have equally
favourable conditions for the modification of old forms, that is the
formation of new races or species. Let the islands become reunited into
a continent; and then the new and old forms would all spread, as far as
barriers, the means of transportal, and the preoccupation of the land by
other species, would permit. Some of the new species or races would
probably become extinct, and some perhaps would cross and blend
together. We should thus have a multitude of forms, adapted to all kinds
of slightly different stations, and to diverse groups of either
antagonist or food-serving species. The oftener these oscillations of
level had taken place (and therefore gener