CHAP. XVI.] SUMMARY AND CONCLUSION. 157 



being due to a radical difference of type, and therefore not 

 indicative of climate. The early European flora seems to have 

 been a portion of that which now exists only in the tropical and 

 sub-tropical lands of the Eastern Hemisphere ; and, as much of 

 this flora still survives in Australia, Tasmania, Japan, and the 

 Cape of Good Hope, it does not necessarily imply more than a 

 warm and equable temperate climate. The early North Ameri- 

 can flora, on the other hand, seems to have been essentially the 

 same in type as that which now exists there, and which, in the 

 Miocene period, was well represented in Europe ; and it is such 

 as now flourishes best in the warmer parts of the United States. 

 But whatever conclusion we may arrive at on the question of 

 climate, there can be no doubt as to the distinctness of the floras 

 of the ancient Nearctic and Palsearctic regions ; and the view 

 derived from our study of their existing and extinct faunas — 

 that these two regions have, in past times, been more clearly 

 separated than they are now — receives strong support from the 

 unexpected evidence now obtained as to the character and muta- 

 tions of their vegetable forms, during so vast an epoch as is 

 comprised in the whole duration of the Tertiary period. 



The general phenomena of the distribution of living animals, 

 combined with the evidence of extinct forms, lead us to con- 

 clude that the Paltearctic region of early Tertiary times was, 

 for the most part, situated beyond the tropics, although it pro- 

 bably had a greater southward extension than at the present 

 time. It certainly included much of North Africa, and perhaps 

 reached far into what is now the Sahara ; while a southward 

 extension of its central mass may have included the Abyssinian 

 highlands, where some truly Palsearctic forms are still found. 

 This is rendered probable by the fossils of Perim Island a little 

 further east, which show that the characteristic Miocene fauna 

 of South Europe and North India prevailed so far within the 

 tropics. There existed, however, at the extreme eastern and 

 western limits of the region, two extensive equatorial land-areas, 

 our Indo-Malayan and West African sub-regions — both of which 

 must have been united for more or less considerable periods 

 with the northern continent. They would then have received 



