Now, on the hypothesis of evolution, there is no sort of difficulty in admitting that the 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 oppose the hypothesis that the older are the progenitors of the more recent forms, while, in some cases, they distinctly favour that hypothesis.  The period in tine and the changes in physical geography represented by the nummulitic deposits are undoubtedly very great, while the remains of Middle Eocene and Older Eocene Mammals are comparatively few.  The general facies of the Middle Eocene Fauna, however,