mate or inanimate world have
occurred to restrict the range which they may once have obtained. As a
general rule, however, species, common to many distant provinces, or
those now found to inhabit very distant parts of the globe, are to be
regarded as the most ancient. Numerically speaking, they may not perhaps
be largely represented, but their wide diffusion shows that they have
had a long time to spread themselves, and have been able to survive many
important revolutions in physical geography.

After so much evidence has been brought to light by the geologist, of
land and sea having changed places in various regions since the existing
species were in being, we can feel no surprise that the zoologist and
botanist have hitherto found it difficult to refer the geographical
distribution of species to any clear and determinate principles, since
they have usually speculated on the phenomena, upon the assumption that
the physical geography of the globe had undergone no material alteration
since the introduction of the species now living. So long as this
assumption was made, the facts relating to the geography of plants and
animals appeared capricious in the extreme, and by many the subject was
pronounced to be so full of mystery and anomalies, that the
establishment of a satisfactory theory was hopeless.[990]

_Centres from which plants have been diffused._--Some botanists
conceived, in accordance with the hypothesis of Wildenow, that mountains
were the centres of creation from which the plants now inhabiting large
continents have radiated; to which De Candolle and others, with much
reason, objected, that mountains, on the contrary, are often the
barriers between two provinces of distinct vegetation. The geologist who
is acquainted with the extensive modifications which the surface of the
earth has undergone in very recent geological epochs, may be able,
perhaps, to reconcile both these theories in their application to
different regions.

A lofty range of mountains, which is so ancient as to date from a period
when the species of animals and plants differed from those now living,
will naturally form a barrier between contiguous provinces; but a chain
which has been raised, in great part, within the epoch of existing
species, and around which new lands have arisen from the sea within that
period, will be a centre of peculiar vegetation.

"In France," observes De Candolle, "the Alps and Cevennes prevent a
great number of th