Boundary in South America. 7 



Andine geosynclino with the formation of the South 

 Atlantic basin. 



Part I. — Origin and history of Patagonian Molluscan 



Faunas. 



In contrast with the northern hemisphere, where the 

 negative phase of the Wealden can be observed from the 

 Vistula River to Dakota, 18 the period which corresponds 

 to the Jurassic-Cretaceous boundary and a great part of 

 the Lower Cretaceous signifies in the southern hemi- 

 sphere one of the culminating points of marine faunistic 

 development; for in the creation of a South Andine 

 province not only Mediterraneo-European, Central Asi- 

 atic and Boreal fauna! elements were associated, but 

 there was a further evolution of independent and charac- 

 teristic elements in this local biologic center. 19 



The Upper Jurassic and Lower Cretaceous types of 

 the South Andine faunas are spread over a wide area 

 from Texas and Mexico to the extreme south, passing 

 the Equator and into southern latitudes with rare uni- 

 formity. They occur on the western border of the 

 ancient Brazilo-Ethiopian Continent, showing little or no 

 visible dependence on either latitude or climate. Uhlig 

 pointed out the probability that the center of evolution 

 of this South Andine fauna had to be looked for south 

 of the Brazilo-Ethiopian Continent, in the vicinity of 

 the Antarctic, and he assumed that future investigators 

 with a better knowledge of physical and biological condi- 

 tions in this province would characterize its fauna as an 

 ''Austral Fauna." 



On the basis of Favre's 20 publication, we may suppose 

 that within the area of this province (the Chile-Pata- 



18 E. Suess, Antlitz der Erde, III 2, p. 91, Leipzig and Vienna, 1909. — 

 See also the symposium held by the Geological Society of America with 

 remarks on this matter by Osborn, Lee, Mook, Lull, Berry and Stanton, 

 Bulletin of the Society, vol. 26, Sept., 1915. 



10 As such characteristic elements of the South Andine province may be 

 regarded for instance: Steueroceras Cossm. (=Odontoceras Steuer) or 

 Satchericeras Stanton. See the remarks of Uhlig on the South Andine 

 elements in his two publications: Fauna der Spiti-Schiefer des Himalaya, 

 ihr geologisches Alter und ihre Weltstellung. Denkschriften d. Akad. der 

 Wissensch., Wien, Math. -Nat. Klasse, vol. 85, pp. 597 etc., 1910. — Die 

 marinen Reiche des Jura und der Unterkreide, Mitt. Geol. Gesellsch., Wien, 

 4, pp. 423 etc., 1911. 



20 Die Ammoniten der unteren Kreide Patagoniens, N. Jahrb. Min., 

 Beil.-Bd., 25, 1908. — See also T. W. Stanton, The marine Cretaceous inver- 

 tebrates, Reports of the Princeton University Expeditions to Patagonia, 

 1896-1899, vol. 4, 1901. 



