iocene Austro-Columbian province.

Nor is it less probable that the characteristic types of Australian
Mammalia were already developed in that region in Miocene times.

But Austro-Columbia presents difficulties from which Australia is free;
_Cantelidoe_ and _Tapirdoe_ are now indigenous in South America as they
are in Arctogaea; and, among the Pliocene Austro-Columbian mammals, the
Arctogaeal genera _Equus, Mastodon,_ and _Machairodus_ are numbered. Are
these Postmiocene immigrants, or Praemiocene natives?

Still more perplexing are the strange and interesting forms _Toxodon,
Macrauchenia, Typotherium_, and a new Anoplotherioid mammal
(_Homalodotherhon_) which Dr. Cunningham sent over to me some time ago
from Patagonia. I confess I am strongly inclined to surmise that these
last, at any rate, are remnants of the population of Austro-Columbia
before the Miocene epoch, and were not derived from Arctogaea by way of
the north and east.

The fact that this immense fauna of Miocene Arctogaea is now fully and
richly represented only in India and in South Africa, while it is shrunk
and depauperised in North Asia, Europe, and North America, becomes at
once intelligible, if we suppose that India and South Africa had but a
scanty mammalian population before the Miocene immigration, while the
conditions were highly favourable to the new comers. It is to be supposed
that these new regions offered themselves to the Miocene Ungulates, as
South America and Australia offered themselves to the cattle, sheep, and
horses of modern colonists. But, after these great areas were thus
peopled, came the Glacial epoch, during which the excessive cold, to say
nothing of depression and ice-covering, must have almost depopulated all
the northern parts of Arctogaea, destroying all the higher mammalian
forms, except those which, like the Elephant and Rhinoceros, could adjust
their coats to the altered conditions. Even these must have been driven
away from the greater part of the area; only those Miocene mammals which
had passed into Hindostan and into South Africa would escape decimation
by such changes in the physical geography of Arctogaea. And when the
northern hemisphere passed into its present condition, these lost tribes
of the Miocene Fauna were hemmed by the Himalayas, the Sahara, the Red
Sea, and the Arabian deserts, within their present boundaries.

Now, on the hypothesis of evolution, there is no sort of difficulty in
admitting that the