ely related (in having the giraffe,
hippopotamus, and certain musk-deer) to southern Africa than it now is;
for southern and eastern Africa deserve, if we divide the world into
five parts, to make one division by itself. Turning to the dawn of the
Tertiary period, we must, from our ignorance of other portions of the
world, confine ourselves to Europe; and at that period, in the presence
of Marsupials{393} and Edentata, we behold an _entire_ blending of those
mammiferous forms which now eminently characterise Australia and S.
America{394}.

{392} The word _hyaena_ is erased. There appear to be no fossil
Hyaenidae in S. America.

{393} See note 1{390}, p. 175, also _Origin_, Ed. i. p. 340, vi. p. 486.

{394} <Note by the author.> And see Eocene European mammals in
N. America.

If we now look at the distribution of sea-shells, we find the same
changes in distribution. The Red Sea and the Mediterranean were more
nearly related in these shells than they now are. In different parts of
Europe, on the other hand, during the Miocene period, the sea-shells
seem to have been more different than at present. In{395} the Tertiary
period, according to Lyell, the shells of N. America and Europe were
less related than at present, and during the Cretaceous still less like;
whereas, during this same Cretaceous period, the shells of India and
Europe were more like than at present. But going further back to the
Carbonaceous period, in N. America and Europe, the productions were much
more like than they now are{396}. These facts harmonise with the
conclusions drawn from the present distribution of organic beings, for
we have seen, that from species being created in different points or
areas, the formation of a barrier would cause or make two distinct
geographical areas; and the destruction of a barrier would permit their
diffusion{397}. And as long-continued geological changes must both
destroy and make barriers, we might expect, the further we looked
backwards, the more changed should we find the present distribution.
This conclusion is worthy of attention; because, finding in widely
different parts of the same main division of the world, and in volcanic
islands near them, groups of distinct, but related, species;--and
finding that a singularly analogous relation holds good with respect to
the beings of past times, when none of the present species were living,
a person might be tempted to believe in some mystica