e 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 specialized 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 change which took
pl