640 HISTORICAL GEOLOGY 



that the intermigration was so great as to make the life of the two 

 continents identical at the beginning of the Oligocene, for this was 

 far from being the case. 



Following the period of land connections at the beginning of the 

 Oligocene, the Old and the New World were again isolated and inde- 

 pendent evolution was permitted. 



Miocene African Invasion. — The similarity of the life of Europe 

 and of North America indicates that these continents, as well as the 

 East Indies, were united during the Miocene (Fig. 563) ; but the dis- 

 similarity of that of South America and Australia shows that these 

 southern continents were separated from the others. The appear- 

 ance in the Lower Miocene of Africa and Europe of ancestral elephants 

 whose development had been taking place in Africa or some adjoining 

 region, during the earlier portion of the Tertiary, shows that these 

 continents of the Old World were then united, for the first time 

 perhaps, since the early Eocene. The mastodons and rhinoceroses 

 migrated to America at this time, and other tribes unquestionably 

 came with them. They are believed to have reached here by way of 

 the Alaskan land connection. These strangers had little effect on 

 the life of the New World, as is shown by the development in America 

 of its own pigs, oreodonts (p. 619), deer (p. 618), antelopes (p. 619), 

 camels (p. 615), horses (p. 608), etc. Although the continental con- 

 nections were well-established between Europe, Asia, Africa, and 

 North America in the Miocene and continued throughout the epoch, 

 permitting the spread into North America of mastodons, rhinoceroses, 

 and probably other mammals, yet many of the important races of 

 the New World — such as the camels, llamas, ancestral horses, and 

 ancestral American deer — were confined to this continent; and 

 animals equally characteristic of the Old World — true rhinoceroses, 

 African and Asiatic monkeys, bears, lynxes, foxes, hyenas, true 

 antelopes — are not known to have migrated to North America 

 at this time. 



Pliocene South American Invasion and Intermigration between 

 the Old and New Worlds. — With the connection of South America 

 and North America in the Pliocene, all of the continents of the world 

 with the exception of Australia were united, and widespread migra- 

 tion occurred. 



South America seems to have been isolated from the rest of the 

 world from early Eocene times until the Pliocene. Its fauna, before 

 the Pliocene connection with North America was established, was 



