158 ZOOLOGICAL GEOGRAPHY. [PART in. 



from it such of the higher vertebrates as were best adapted for 

 the peculiar climatal and organic conditions which everywhere 

 prevail near the equator ; and these would be preserved, under 

 variously modified forms, when they had ceased to exist in 

 the less favourable and constantly deteriorating climate of the 

 north. At later epochs, both these equatorial lands became 

 united to some part of the great South African continent (then 

 including Madagascar), and we thus have explained many of 

 the similarities presented by the faunas of these distant, and 

 generally very different countries. 



During the Miocene period, when a subtropical climate pre- 

 vailed over much of Europe and Central Asia, there would be no 

 such marked contrast as now prevails between temperate and 

 tropical zones ; and at this time much of our Oriental region, 

 perhaps, formed a hardly separable portion of the great Palsearctic 

 land. But when, from unknown causes, the climate of Europe 

 became less genial, and when the elevation of the Himalayan 

 chain and the Mongolian plateau caused an abrupt difference of 

 climate on the northern and southern sides of that great moun- 

 tain barrier, a tropical and a temperate region were necessarily 

 formed ; and many of the animals which once roamed over the 

 greater part of the older and more extensive region, now became 

 restricted to its southern or northern divisions respectively. 

 Then came the great change we have already described (vol. i. 

 p. 288), opening the newly-formed plains of Central Africa to the 

 incursions of the higher forms of Europe ; and following on this, 

 a still further deterioration of climate, resulting in that marked 

 contrast between temperate and tropical faunas, which is now one 

 of the most prominent features in the distribution of animal as 

 well as of vegetable forms. 



It is not necessary to go into any further details here, as we 

 have already, in our discussion of the origin of the fauna of. the 

 several regions, pointed out what changes most probably occurred 

 in each case. These details are, however, to a great extent 

 speculative; and they must remain so till we obtain as much 

 knowledge of the extinct faunas and past geological history of 

 the southern lands, as we have of those of Europe and North 



