ANCIENT CONTINENTS. 



345 



Thus, the elephants and the camels appear to have 

 descended from what were once exclusively American 

 types, while the opossums were as certainly European. 

 Many groups, however, never passed out of the continent 

 in which they originated — the civets, hygenas, and the 

 giraffes being wholly eastern, while the Oreodontidae 

 and Brontotheridse were no less exclusively western. 



South America seems to have been united to the 

 northern continent once at least in Secondary or early 

 Tertiary times, since it was inhabited in the Eocene 

 period by many forms of mammalia, such as rodents, 

 felines, and some ancient forms of Ungulata. It must 

 also have possessed the ancestors of the Edentata 

 (though they have not yet been discovered), or we 

 should not find such a variety of strange and gigantic 

 forms of this order in later Tertiary deposits in this 

 part of the world only. During the greater part of 

 the Tertiary period, therefore. South America must 

 have been separated from the North and protected from 

 incursions of the higher forms of mammalia which 

 were there so abundant. Thus only does it seem pos- 

 sible to understand the unchecked development of so 

 many large but comparatively helpless animals as the 

 Edentata of the Pampas and the Brazilian caves — a 

 development only comparable with that of the Australian 

 marsupials, still more completely shut off from all 

 competition with higher forms of life. 



In Africa the evidence of a long period of insulation 

 is somewhat more complex and less easily apparent, but, 

 it seems to me, equally conclusive. We have first, the 

 remarkable fauna of Madagascar, in which lemurs and 

 insectivora predominate, with a few low forms of 



