We find then, that even at so early a stage of our inquiries we meet with a problem in distribution by no means easy to solve. How are we to explain the banishment from Europe in so short a space of time (geologically speaking) of so many forms of life now characteristic of warmer countries, and this too during a period when the climate of Central Europe was itself becoming warmer? Such a change must almost certainly have been due to changes of physical geography, which we shall be better able to understand when we have examined the preceding Pliocene period. We may here notice, however, that so far as we yet know, this great recent change in the character of the fauna is confined to the western part of the Palæarctic region. In caves in the Altai Mountains examined by Prof. Brandt, a great collection of fossil bones was discovered. These comprised the Siberian rhinoceros and mammoth, and the cave hyæna; but all the others, more than thirty distinct species, are now living in or near the same regions. We may perhaps impute this difference to the fact that the migration of Southern types into this part of Siberia was prevented by the great mountain and desert barrier of the Central Asiatic plateau; whereas in Europe there was at this time a land connection with Africa. Post-pliocene deposits and caverns in Algeria have yielded remains resembling the more southern European types of the Post-pliocene period, but without any admixture of Arctic forms; showing, as we might expect, that the glacial cold did not {112}extend so far south. We have here remains of _Equus_, _Bos_, _Antilope_, _Hippopotamus_, _Elephas_, _Rhinoceros_, _Ursus_, _Canis_, and _Hyæna_, together with _Phacochoerus_, an African type of swine which has not occurred in the European deposits. It is perhaps to the earlier portion of this period that the _Merycotherium_ of the Siberian drift belongs. This was an animal related to the living camel, thus supporting the view that the _Camelidæ_ are essentially denizens of the extra-tropical zone. PLIOCENE PERIOD. _Primates._--We here first meet with evidence of the existence of monkeys in Central Europe. Species of _Macacus_ have left remains not only in the Newer Pliocene of the Val d'Arno in Italy, but in beds of the same age at Grays in Essex; while _Semnopithecus_ and _Cercopithecus_, genera now confined to the Oriental and Ethiopian regions respectively, have been found in the Pliocene deposits of the South of France and Italy. _Carnivora._--Most of the genera which occurred in the Post-Pliocene are found here also, and many of the same species. Few new forms appear, except _Hyænarctos_, a large bear with characters approaching the hyænas, and _Pristiphoca_, a new form of seal, both from the Older Pliocene of France; and _Galecynus_, a fox-like animal intermediate between _Canis_ and _Viverra_, from the Pliocene of Oeninghen in Switzerland.