Boundary in South America. 9 



by future exploration. Concerning the evolution of 

 South American terrestrial faunae, H. v. Ihering 23 has 

 the merit of having emphasized the great importance of 

 "Archinotis," the sunken Antarctic Continent of the 

 past. The idea of Gaudry, 24 that the manifold Patago- 

 nian faunas required for their evolution a much larger 

 area than that existing at the present time, thus finds a 

 certain validity. In the same way, Ameghino claimed a 

 greater Patagonia of the past. The known part of the 

 homes of the fossil Patagonian faunas does not have the 

 features of an "asylum" in the sense of Suess. As in 

 the case of New Mexico, where occur the placental mam- 

 mals of Laurentian correlation, Patagonia is only the 

 border of an old continent of the past. Antarctica thus 

 reveals itself during Cretaceous and Tertiary time as an 

 important center for the evolution of the terrestrial as 

 well as the marine faunae of Patagonia. 



Towards the close of the Cretaceous, perhaps when the 

 Senonian Sea still partly covered the southern margin 

 of the old Brazilo-Ethiopian Continent, 25 this continental 

 area experienced one of the greatest diastrophic events 

 of its history; on its western border, in the zone of the 

 Andine geosyncline took place the first phase of oro- 

 genetic movements characterized by lateral pressure. 26 

 Thus ended the series of marine Jurassic and Cretaceous 

 transgressions from the west side and thus were initiated 

 the events leading to the present geologic structure. 

 The breaking down of large parts of the old continent 

 and the consequent formation of the South Atlantic basin 

 may be primarily regarded as the result of this phenom- 

 enon, which opened the way for a series of marine trans- 

 gressions from the Atlantic side, and in great part 

 determined the geologic and physiographic character of 

 the present Patagonia, outside the Cordillera. 



These transgressions of Tertiary time stretched over 

 an ancient basement, the structural and genetic knowledge 

 of which has not reached the settled stage. With regard 



53 Archhelenis und Archinotis, Leipzig, 1907. 



24 fitude sur une portion du Monde Antarctique, Annales de Paleontologie 

 1, fase. 3, 1906. (Cited according to E. Suess, Antlitz der Erde, III 2, 

 p. 772.) 



23 Hauthal, Wilckens und Paulcke, Die Obere Kreide Siidpatagoniens und 

 ihre Fauna, Berichte Nat. Gesellsch. Freiburg i. Br., 15, 1907. 



26 H. Keidel, Die neueren Ergebnisse der staatlichen geologischen TJnter- 

 suchungen in Argentinien, Compte rendu du Xl-eme Congres Geol. Inter- 

 nationale, p. 1137, Stockholm, 1910. 



