230 ORIGIN OF LIFE IN AMERICA 



into North America, while the monkeys (Primates) disappear 

 for ever from the continent. 



In his restoration of Oligocene conditions in North 

 America, Professor Schuchert still depicts North America 

 as being joined in the far north by wide land bridges with 

 Asia and Europe, while practically submerging the whole of 

 the West Indies. As we shall learn later on, an intimate 

 relationship exists between the shallow water marine forms 

 of early Tertiary European and Antillean deposits, and this 

 has given rise to the suggestion that a land bridge must then 

 have united Europe and the Antilles. If 'my view should be 

 substantiated, that the resemblance in the Oligocene faunas of 

 Europe and south-western North America is due to the exis- 

 tence in Oligocene times of a mid-Atlantic land bridge, the 

 West Indian area, of course, could not have been submerged 

 at that time. 



After a short phase of independent evolution, during which 

 the Oligocene deposits of western North America insensibly 

 pass into Miocene ones, the succeeding Middle Miocene beds 

 are characterised by the appearance of a large number of new 

 forms, among which the elephants (Proboscidea) deserve 

 special mention. Some of these new immigrants are, ap- 

 parently, of African, others of Eurasiatic origin. The 

 Miocene beds of Europe and of America are remarkable for 

 the similarity of their fauna. The conclusion deduced from 

 this fact by Professor Osborn * is that the North American 

 middle Miocene formations contain animals which first appear 

 in the lower Miocene of Europe, just as the American lower 

 Miocene contains animals that first appear in the upper 

 Oligocene of Europe. 



Now it is quite possible that while the faunistic inter- 

 change between western Europe and western North America 

 took place by means of one land connection during early 

 Tertiary times, this land bridge was replaced later on by an 

 entirely different one. Professor Deperetf had some such 

 idea in his mind in expressing the view that the Miocene and 

 Pliocene migrations from Europe to America probably 

 arrived by way of Asia and the Bering Strait, while the earlier 



* Osborn, H. F., " Cenozoic Mammal Horizons," p. 76. 



t Dep6ret, 0., " Transformations of the Animal World," p. 314. 



