a judgment to be formed, the same
law appears to have held good for all the earlier Mesozoic _Mammalia_. Of
the Stonesfield slate mammals, one, _Amphitherium_, has a definitely
Australian character; one, _Phascolotherium_, may be either Dasyurid or
Didelphine; of a third, _Stereognathus_, nothing can at present be said.
The two mammals of the Trias, also, appear to belong to Australian
groups.

Every one is aware of the many curious points of resemblance between the
marine fauna of the European Mesozoic rocks and that which now exists in
Australia. But if there was this Australian facies about both the
terrestrial and the marine faunae of Mesozoic Europe, and if there is this
unaccountable and immense break between the fauna of Mesozoic and that of
Tertiary Europe, is it not a very obvious suggestion that, in the
Mesozoic epoch, the Australian province included Europe, and that the
Arctogaeal province was contained within other limits? The Arctogaeal
province is at present enormous, while the Australian is relatively
small. Why should not these proportions have been different during the
Mesozoic epoch?

Thus I am led to think that by far the simplest and most rational mode of
accounting for the great change which took place in the living
inhabitants of the European area at the end of the Mesozoic epoch, is the
supposition that it arose from a vast alteration of the physical
geography of the globe; whereby an area long tenanted by Cainozoic forms
was brought into such relations with the European area that migration
from the one to the other became possible, and took place on a great
scale.

This supposition relieves us, at once, from the difficulty in which we
were left, some time ago, by the arguments which I used to demonstrate
the necessity of the existence of all the great types of the Eocene epoch
in some antecedent period.

It is this Mesozoic continent (which may well have lain in the
neighbourhood of what are now the shores of the North Pacific Ocean)
which I suppose to have been occupied by the Mesozoic _Monodelphia_; and
it is in this region that I conceive they must have gone through the long
series of changes by which they were specialised into the forms which we
refer to different orders. I think it very probable that what is now
South America may have received the characteristic elements of its
mammalian fauna during the Mesozoic epoch; and there can be little doubt
that the general nature of the chang