34 Windhausen — The Cretaceous-Tertiary 



Accordingly, the latter case is in contrast to the others, 

 inasmuch as in the northern and central parts of Pata- 

 gonia, the San Jorge overlaps the Upper Cretaceous 

 Variegated Sandstones, or perhaps in special cases 

 directly the old platform of paleozoic or archaic age. 

 The Upper Senonian transgression at Lago Argentino 

 is due to the submergence of a small continental border, 

 and not only the equivalent deposits at Quiriquina, but 

 also their faunistic character, show the Pacific wayiand 

 origin of this transgression. Thus, near the southern 

 point of the South American Continent can be observed 

 the interesting case of the overlapping of marine forma- 

 tions, one of which came from the Pacific, the other from 

 the Atlantic side, indicating in this way diastrophic 

 events of fundamental importance. 



Part III. — Paleo geography of the San Jorge-Formation. 



In the foregoing chapter it was necessary to go into a 

 somewhat detailed examination of local stratigraphic 

 relations. Upon the basis of this knowledge it is pos- 

 sible to determine the ancient shore-lines of the San 

 Jorge-Sea ; and it will now be shown that, at least in the 

 northern part, the ancient structural elements influenced 

 in a remarkable manner the limits of this epicontinental 

 sea (see fig. 3). 



In the north, the sea ended in the region of the Rio 

 Atuel. In the surroundings of Canada Colorada we have 

 studied the most northerly deposits of this period, the 

 base of which is formed by brackish horizons. Close to 

 the north bank of the Rio Diamante (34° 40' S..L. and 

 69° 30' west of Greenwich) there bends down the great 

 granitic batholith, which from here strikes north across 

 the Paso del Portillo, 79 the "zone of Cerro Tupungato, and 

 enters the region of the Cerro del Plata. 80 On the flanks 

 of this great batholith, south of the Rio Diamante, the 

 Variegated Sandstones of Cretaceous age rise up from 

 the foot of the Cordillera towards the heights of the 

 mountain. To the east of this region, on the other side 

 of a large plain appears a new and strange orographic 

 element, the so-called Sierra Pintada, forming a counter- 

 part of the Cordillera in a SE.-NW. direction. This range 

 extends at an acute angle to the very base of the Cordil- 



70 See Darwin, Geological observations etc., pp. 175 etc. 

 80 Stappenbeck, Geologia de la falda oriental de la Cordillera del Plata, 

 Anales Ministerio de Agricultura, Buenos Aires. In press. 



