442 
NATCRE 
[ feb. 24, 1870 
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 representa- 
tives of Zusectivora, of Cheiroptera, of Rodentia, of Carnivora, of 
Artiodactyle, and Perissodactyle Ungulata and of opossum-like 
Marsupials. No Australian type of marsupial has been dis- 
covered in the upper Eocene, nor any Edentate mammal. The 
genera (except in the case perhaps of some of the /ysectivora, 
Cheiroptera, and Rodentia) are different from those of the Miocene 
epoch, but present 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 
least 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 
Faunz 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 time and the changes in physical 
geography, represented by the nummulitic deposits, are un- 
doubtedly very great, while the remains of middle Eocene and 
older Eocene Mammals are comparatively few. The general 
facies of the middle Eocene Fauna, however, is quite that of 
the upper. 
The older Eocene, pre-nummulitic mammalian Fauna, con- 
tains Bats, two genera of Carnivora, three genera of Ungulata 
(probably all perissodactyle), and a didelphid marsupial. All 
these forms, except perhaps the Bat and the Opossum, belong 
to genera which are not known to occur out of the lower Eocene. 
The Coryphodon, however, appears to have been allied to the 
Miocene and later Tapirs; while P#zo/ophus, in its skull and 
dentition, curiously partakes of both artiodactyle and perisso- 
dactyle characters. The third trochanter upon its femur, and 
its three-toed hind foot, however, appear definitely to fix its 
position in the latter division. 
There is nothing, then, in what is known of the older Eocene 
mammals of the Arctogzeal province to forbid the supposition 
that they stood in an ancestral relation to those of the Calcaire 
Grossier and the Gypsum of the Paris basin ; and that our present 
fauna, therefore, is directly derived from that which already existed 
in Arctogzea at the commencement of the Tertiary period. But 
if we now cross the frontier between the Cainozoic and the Meso- 
zoic Faunze, as they are preserved within the Arctogzeal area, we 
meet with an astounding change, and what appears to be a com- 
plete and unmistakeable break in the line of biological continuity. 
Among the twelve or fourteen species of Mammalia which 
are said to haye been found in the Purbecks, not one is a 
member of the orders Chetrvoptera, Rodentia, Ungulata, or Car- 
nivora, which are so well represented in the Tertiaries. No 
Tnsectivora are certainly known, nor any opossum-like Marsupials. 
Thus there is a vast negative difference between the Cainozoic 
and the Mesozoic mammalian Faun of Europe. But there is a 
still more important positive difference, inasmuch as all these Mam- 
malia appear to be Marsupials belonging to Australian groups ; 
and thus appertaining to a different distributional province from the 
Eocene and Miocene marsupials, which are Austro-Columbian. 
So far as the imperfect materials which exist enable a judgment 
to be formed, the same law appear to have held good for all the 
earlier mesozoic Mammalia. Of the Stonesfield slate mammals, 
one, Amphitherium, has a definitely Australian character ; one, 
Phaseolotherium, may be either Dasyurid or Didelphine ; ofa third, 
Stereognathus, nothing can at present be said. The two mam- 
mals of the Trias, also, appear to belong to Australian groups. 
Everyone 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 Austra- 
lian facies about both the terrestrial and the marine Faune 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 
Arctogzal province was contained within other limits? The 
Arctogzeal 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 great change in 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 change which took place at the end of the 
Mesozoic epoch in Europe, was the upheaval of the eastern and 
northern regions of the Mesozoic sea bottom into a westward 
extension of the Mesozoié continent, over which the Mammalian 
Fauna, by which it wasalready peopled, gradually spread. This 
invasion of the land was prefaced by a previous invasion of 
the Cretaceous sea by modern forms of mollusca and fish. 
It is easy to imagine how an analogous change might come about 
in the existing world. There is, at present, a great difference 
between the Fauna of the Polynesian Islands‘and that of the west 
coast of America. The animals which are leaving their spoils 
in the deposits now forming in these localites are widely different. 
Hence, if a gradual shifting of the deep sea, which at present 
bars migration, between the easternmost of these islands and 
America took place to the westward, while the American side of 
the sea-bottom was gradually upheaved, the palzontologist of 
the future would find, over the Pacific area, exactly such a change 
as I am supposing to have occurred in the North Atlantic area at 
the close of the Mesozoic period. An Australian Fauna would 
be found underlying an American Fauna, and the transition from 
the one to the other would be as abrupt as that between the Chalk 
and lower Tertiaries. And as the drainage area of the newly- 
formed extension of the American continent gave rise to rivers 
and lakes, the mammals mired in their mud would differ from 
those of like deposits on the Australian side just as the Eocene 
mammals differ from those of the Purbecks. 
How do similar reasonings apply to the other great change of 
life—that which took place at the end of the Palaeozoic period ? 
In the Triassic epoch, the distribution of the dry land and ot 
terrestrial vertebrate life appears to have been, generally, similar 
to that which existed in the Miocene epoch; so that the 
Triassic continents and their Faunz seem to be related to the 
Mesozoic lands and their Faunce, just as those of the Miocene 
epoch are related to those of the present day. 
In fact, as I have recently endeavoured to prove to the Society, 
there was an Arctogzeal continent and an Arctogzeal province of 
distribution in Triassic times as there is now. And the Sawrop- 
sida and Marsupialia which constituted that fauna were, I doubt 
not, the progenitors of the Sauvopsida and Marsupialia of the 
whole Mesozoic epoch. 
Looking at the present terrestrial fauna of Australia, it appears 
to me to be very probable that it is essentially a remnant of the 
Fauna of the Triassic, or even of an earlier, age ; in which case 
Australia must at that time have been in continuity with the 
Arctogzeal continent. 
But now comes the further inquiry, Where was the highly- 
differentiated Sauropsidan Fauna of the Trias in Palaeozoic 
times? The supposition that the Dinosaurian, Crocodilian, 
Dicynodontian, and Plesivsaurian types were suddenly created at 
the end of the Permian epoch may be dismissed, without further 
consideration, as a monstrous and unwarranted assumption. 
The supposition that all the types were rapidly differentiated 
out of Zacertilia, in the time represented by the passage from the 
