Boundary in South America. 15 



Zealand provinces. But in general, future studies will 

 attach more importance to the independence and pecu- 

 liarity of the faunistic elements, and these features may 

 he regarded as due to a relatively isolated development 

 in the South Atlantic and Antarctic regions. Thus, for 

 the third time in the course of earth history, Antarctic 

 becomes the center of singular marine life. The appar- 

 ent poverty of the San Jorge-fauna cannot be adjudged 

 an original and peculiar feature, being rather the con- 

 sequence of insufficient collections and bad preservation 

 of the fossils. The real wealth of this fauna is very 

 likely buried in the depths of the Antarctic Ocean. In 

 the succession of marine faunas that sprang from this 

 biologic center of the far south, the San Jorge-fauna is 

 as important as the foregoing Lower Cretaceous and 

 Senonian faunae. It indicates one of the culminating 

 points of marine biologic evolution. 



Pabt II. — Stratigraphy of the San Jorge-Formation. 



According to the definition of Wilckens, 40 the San 

 Jorge-Formation comprises the marine deposits firstly 

 in the neighbourhood of the village of General Roca in 

 the Rio Negro, secondly in the region of the Gulf of St. 

 George, 41 and thirdly the strata with Lahillia luisa 

 Wilck. in the region of the Lago Argentino and Seno de 

 la Ultima Esperanza (Santa Cruz). But while the two 

 first of these formations are in obvious contrast to their 

 base, namely the continental Variegated Sandstones of 

 the Upper Cretaceous, the so-called Luisaen is, even 

 according to "Wilckens himself, closely allied with the 

 ammonite- and baculite-bearing deposits of the Upper 

 Senonian. There is a gradual transition from the lower 

 horizons with ammonites and baculites to the upper 

 ones with Lahillia luisa; and the impoverishment of the 

 ammonite-fauna progresses little by little from top to 

 bottom, although in the strata with Lahillia luisa some 

 ammonites still occur. Wilckens instances three or four 

 mollusca as common types of the Luisaen and the Roca- 

 Salamanca; but there can be no doubt that great faun- 



40 Die Meeresablagerungen der Kreide- und Tertiarformation in Pata- 

 gonien, pp. 135 etc. 



a The so-called Salamanca-Beds which received its name from the Sala- 

 manca-Peak, located about 10 miles at the north of Comodoro Eivadavia 

 (Chubut). 



