differences between the Miocene forms of the mammalian
Fauna and those which exist at present are the results of gradual
modification; and, since such differences in distribution as obtain are
readily explained by the changes which have taken place in the physical
geography of the world since the Miocene epoch, it is clear that the
result of the comparison of the Miocene and present Faunae is distinctly
in favour of evolution. Indeed I may go further. I may say that the
hypothesis of evolution explains the facts of Miocene, Pliocene, and
Recent distribution, and that no other supposition even pretends to
account for them. It is, indeed, a conceivable supposition that every
species of Rhinoceros and every species of Hyaena, in the long succession
of forms between the Miocene and the present species, was separately
constructed out of dust, or out of nothing, by supernatural power; but
until I receive distinct evidence of the fact, I refuse to run the risk
of insulting any sane man by supposing that he seriously holds such a
notion.

Let us now take a step further back in time, and inquire into the
relations between the Miocene Fauna and its predecessor of the Upper
Eocene formation.

Here it is to be regretted that our materials for forming a judgment are
nothing to be compared in point of extent or variety with those which are
yielded by the Miocene strata. However, what we do know of this Upper
Eocene Fauna of Europe gives sufficient positive information to enable us
to draw some tolerably safe inferences. It has yielded representatives of
_Insectivora_, of _Cheiroptera_, of _Rodentia_, of _Carnivora_, of
artiodactyle and perissodactyle _Ungulata_, and of opossum-like
Marsupials. No Australian type of Marsupial has been discovered in the
Upper Eocene strata, nor any Edentate mammal. The genera (except perhaps
in the case of some of the _Insectivora, Cheiroptera_, and _Rodentia_)
are different from those of the Miocene epoch, but present a remarkable
general similarity to the Miocene and recent genera. In several cases, as
I have already shown, it has now been clearly made out that the relation
between the Eocene and Miocene forms is such that the Eocene form is the
less specialised; while its Miocene ally is more so, and the
specialisation reaches its maximum in the recent forms of the same type.

So far as the Upper Eocene and the Miocene Mammalian Faunae are
comparable, their relations are such as in no way to oppo