The geographical distribution of animals, with a study of the relations ...

—302 ZOOLOGICAL GEOGRAPHY. [part hi.and Malaya to have taken place, we shall perhaps be able toaccount for most of the special affinities they present, with theleast amount of simultaneous elevation of the ocean bed ; whichit must always be remembered, requires a corresponding depressionelsewhere to balance it.Concluding Remarks on the Oriental Region.—We have alreadyso fully discussed the internal and external relations of theseveral sub-regions, that little more need be said. The rich andvaried fauna which inhabited Europe at the dawn of the tertiaryperiod,—as shown by the abundant remains of mammaliawherever suitable deposits of Eocene age have been discovered,proves, that an extensive Palsearctic continent then existed;and the character of the floraisand fauna of the Eocene depositsso completely tropical, that we may be sure there was then nobarrier of climate between it and the Oriental region. At thatearly period the northern plains of Asia were probably underwater, while the great Thibetan plateau and the Himalayan range,had not risen to more than a moderate height, and would havesupported a luxuriant sub*-tropical flora and fauna.The UpperMiocene deposits of northern and central India, and Burmah,agree in their mammalian remains with those of central andsouthern Europe, whileclosely allied forms of elephant, hysena,tapir, rhinoceros, and Chalicotherium have occurred in NorthChina; leading us to conclude that one great fauna thenextended over much of the Oriental and Palsearctic regions.Perim island at the mouth of the Eed Sea, where similarremains are found, probably shows the southern boundary ofthis part of the old Palsearctic region in the Miocene period.Towards the equator there would, of course, be some peculiargroups ; but we can hardly doubt, that, in that wonderful timewhen even the lands that stretched out furthest towards thepole, supported a luxuriant forest vegetation, substantially onefauna ranged over the whole of the great eastern continent of thenorthern hemisphere. During the Pliocene period, however, aprogressive change went on which resulted in the completedifferentiation of the Oriental and Palsearctic faunas. The