Feb. 24, 1870] 
NATURE 
441 
Now the truth which Mr. Darwin perceived and promulgated 
as ‘‘the law of the succession of types” is, that in all these pro- 
vinces the animals found in Pliocene or Pleistocene deposits are 
closely affined to those which now inhabit the same provinces, 
and that conversely, the forms characteristic of other provinces 
are absent. North and South America, perhaps, present one or 
two exceptions to the last rule, but they are readily susceptible 
of explanation. Thus, in Australia, the later tertiary Mammals 
are Marsupials (possibly with exception of the Dog and a Rodent or 
two, as at present). In Austro-Columbia the later tertiary Fauna 
exhibits numerous and varied forms of Platyrhine apes, Rodents, 
Cats, Dogs, Stags, Zdentata, and Opossums; but, as at present, no 
Catarhine apes, no Lemurs, no /zsectivora, Oxen, Antelopes, Rhi- 
noceroses or Dide/phia other than opossums. And, in the wide- 
spread Arctogzeal province, the Pliocene and Pleistocene Mammals 
belong to the same groups as those which now exist in the pro- 
vince. The law of succession of types, therefore, holds good 
for the present epoch as compared with its predecessor. Does 
it equally well apply to the Pliocene Fauna when we com- 
pare it with that of the Miocene epoch? By great good 
fortune an extensive Mammalian Fauna of this epoch has now 
become known, in four very distant portions of the Arctogzeal 
province which do not differ greatly in latitude. Thus 
Falconer and Cautley have made known the Fauna of the 
sub-Himalayas and the Perim Islands; Gaudry that of Attica ; 
many observers that of Central Europe and France ; Leidig, 
that of Nebraska on the eastern flank of the Rocky Mountains. 
The results are very striking. The total Miocene Fauna com- 
prises many genera and species of Catarhine apes, of Bats, of 
Insectivora, of Arctogeeal types of Rodentia, of Proboscidea, of 
Equine Rhinocenti, and Tapirine quadrupeds ; of cameline, 
bovine, antelopine, cervine, and traguline Ruminants; of Pigs 
and Hippopotamuses ; of Viverride and Hyenide among other 
Carnivora ; with £dentata allied to the Arctogeal Ovyete- 
vopus and Manis, and not to the Austro-Columbian Edentates. 
The only type present in the Miocene, but absent in the existing, 
Fauna of Eastern Arctogzea is that of the Didelphide, which, 
however, remains in North America. 
But it is very remarkable, that while the Miocene Fauna of 
the Arctogzeal Province, as a whole, is of the same character as 
the existing Fauna of the same province as a whole, the com- 
ponent elements of the Fauna were differently associated. In 
the Miocene epoch, North America possessed Elephants, 
Horses, Rhinoceroses,’and a great number and variety of Rumi- 
nants and Pigs which are absent in the present indigenous 
Fauna. Europe had its Apes, Elephants, Rhinoceroses, 
Tapirs, Musk-deer, (Giraffes, Hyenas, great Cats, Edentates, 
and opossum-like Marsupials, which have equally vanished 
from its present Fauna. And in Northern India, the African 
types of Hippopotamuses, Giraffes, and Elephants were mixed 
up with what are now the Asiatic types of the latter and with 
Camels, Semnopithecine and Pithecine apes of no less distinctly 
Asiatic forms. 
In fact, the Miocene Mammalian Fauna of Europe and the 
Himalayan regions contains associated together the types which 
are now separately located in the South African and Indian 
sub-provinces of Arctogzea. Now there is every reason to 
believe, on other grounds, that both Hindostan, south of the 
Ganges, and Africa, south of the Sahara, were separated by a 
wide sea from Europe and North Asia, during the middle and 
upper Eocene epochs. Hence it becomes highly probable that the 
well-known similarities and no less remarkable differences 
between the present Faunz of India and South Africa have 
arisen in some such fashion as the following. Sometime during 
the Miocene epoch, possibly when the Himalayan chain was 
elevated, the bottom of the nummulitic sea was upheaved 
and converted into dry land, in the direction of a line extend- 
ing from Abyssinia to the mouth of the Ganges. By this 
means, the Dekhan on the one hand, and South Africa on 
the other, became connected with the Miocene dry land and 
with one another. The Miocene Mammals spread gradually 
over this intermediate dry land, and if the condition of its 
eastern and western ends offered as wide contrasts as the valleys 
of the Ganges and Arabia do now, many forms which made their 
way into Africa must have been different from those which 
reached the Dekhan, while others might pass into both these 
sub-provinces. 
That there was a continuity of dry land between Europe 
and North America during the Miocene epoch, appears to me to 
be a necessary consequence; the fact that many genera or terres- 
trial Mammals such as Castor, Hystrix, Elephas, Mastodon, Equus, 
fiipparion, Hipparitherium, Rhinoceros,Cervus, Amphicyon, Hyen- 
arctos, and Machairodus, are common to the Miocene formations 
of the two areas, and have as yet been found (except perhaps 
Hipparitherium) 1 no deposit of earlier age. Whether this 
connection took place by the east, or by the west, or by both sides 
of the old world, there is at present no certain evidence, and 
the question is immaterial to the present argument ; but, as there 
are good grounds for the belief that the Australian province and 
the Indian and South African sub-provinces were separated by 
sea from the rest of Arctogzea before the Miocene epoch, so it has 
been rendered no less probable by the investigations of Mr. 
Carrick Moore and Prof. Duncan that Austro-Columbia was 
separated by sea from North America, during a large part of the 
Miocene epoch. 
It is unfortunate that we have no knowledge of the Miocene 
Mammalian Fauna of the Australian and Austro-Columbian 
provinces. But seeing that not a trace of a Platyrhine ape, of a 
Procyonine carnivore, of a characteristically South American 
Rodent, of a Sloth, an Armadillo, or an Ant-eater, has yet been 
found in Miocene deposits of Arctogzea, I cannot doubt that 
they already existed in the Miocene Austro-Columbian province. 
Noris 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—Camelide and Tafiride are now indigenous in South 
America as they are in Arctogeea, and among the Pliocene 
Austro-Columbian mammals, the Austro-Columbian genera 
Equus, Mastodon, and Machatrodus are numbered. Are these 
post-Miocene immigrants, or prae-Miocene natives? 
Still more perplexing are the strange and interesting forms 
Toxodon, Macrauchenia, and Typotherium ; and a new Anoplo- 
theriod mammal (Oma/odotherium) 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 Arctogzea by way of 
the north and east. 
The fact that this immense Fauna of Miocene Arctogzea is now 
fully and richly represented only in India and 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 favour- 
able 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-cover- 
ing, must have almost depopulated all the northern parts of 
Arctogzea, destroying all the higher mammalian forms except 
those which, like the elephant and rhinoceros, could adjust 
their coats to the altered condition. Even these must have 
been driven away from the greater part of the area. Only 
those Miocene mammals which had passed into Hindo- 
stan and into South Africa would escape decimation by these 
changes in the physical geography of Arctogeea. 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 diffi- 
culty in admitting that the differences between the Miocene forms 
of the Mammalian Fauna and those which exist now, 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 com- 
parison of the Miocene and present Faunce 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 pre- 
tends to account for them. It is, indeed, a conceivable supposition 
that every species of Rhinoceros and every species of Hyzena, 
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 dis- 
tinct evidence of the fact, I refuse to run the risk of insulting 
