MIGRATION OF TERRESTRIAL VERTEBRATES 309 



Tertiary fauna as early as that of the horizon of 

 Puerco. North America, it appeared, therefore 

 should be looked upon as the true cradle of the 

 Placentals, who early emigrated to Europe across 

 the territories of the North Atlantic which had 

 risen from the sea. 



Quite recently, however, Florentine Ameghino 

 has attempted to raise the whole problem anew by 

 maintaining that the Notostylops strata in Pata- 

 gonia are of the upper Cretacean age, and that, 

 consequently, it was from South America that the 

 migrations of the Placentals issued. According to 

 the Argentine savant, these animals must first 

 have reached the African continent then joined to 

 America (the Archellenis of Ihering), then Europe 

 across the Mesogean, and, lastly, North America. 

 The circle of migration would thus have been 

 nearly complete. This seductive hypothesis is un- 

 fortunately based on the consideration of the Creta- 

 cean age as that of the Patagonian fauna, which is 

 contested by many geologists, this fauna being 

 referred by them to, at least, the lowest point of 

 the Eocene formations. 



Whatever may be the solution reserved in the 

 future to this important problem, we must, at all 

 events, admit the fact of extensive migrations, 

 which at the commencement of the lower Eocene 

 dispersed over the globe from the United States to 

 Europe, and as far as the lowest point of South 

 America, representatives of several already per- 

 fectly differentiated orders of placental Mammals. 



To follow from the lower Eocene the complex 

 series of migrations and interchanges of fauna 



