42 Windhausen — The Cretaceous -Tertiary 



kind in the largo depressions between the various chains 

 of the Pampine Sierras. If so, a widespread brackish 

 epicontinental sea may have connected through the Alto 

 Pencoso with the San Jorge-Sea. 



It is obvious that the known San Jorge represent only 

 a very small remnant. Its real marine life is hidden 

 beneath the South Atlantic or remains unseen in the 

 Antarctic. In the north but a relatively small branch is 

 known, which resembled an inland sea, like for instance 

 the present Baltic Sea. In the south, the connection with 

 the open ocean was wider and more extensive; but our 

 knowledge does not pass the limits of the littoral zone. 



The manner in which the northern branch of the San 

 Jorge-Sea was bounded by old structural elements, finds 

 certain Central European analogies. Between the Baltic 

 Shield on the one side and the Variscian Mountain on 

 the other, lay the region of Mesozoic and Cenozoic trans- 

 gressions alternating with periods of folding. Just as 

 the old horsts play a part in the folding of the great 

 Central European geosyncline, so between the ancient 

 Patagonian mass on one side and the Permian and Pre- 

 permian structural elements on the other, can be observed 

 the process of preparation and creation of a new geo- 

 syncline. It is, too, conceivable that in the geologic 

 future this geosyncline may develop as a counterpart of 

 the great Andine geosyncline of the Mesozoic. But, at 

 present neither the magnitude of sedimentation nor the 

 consequent subsidence is observable ; while apart from 

 the relatively feeble movements of the later Tertiary, no 

 process of folding has affected this geosynclinal area. 



The sediments of the San Jorge may be divided into 

 two different lithologic facies, agreeing also with some 

 faunistic features : In the north are the Roca-Beds and 

 in the south the Salamanca. The northern facies is 

 characterized in its lower half by a clayey, gypsum-bear- 

 ing component. Gypsum of considerable thickness 

 occurs in the region of the Rio Grande and near Roca. 

 The clays ("Capas del Jaguel" in the surroundings of 

 the Sierra Auca Mahuida) and the gypsum are at least 

 in part of terrigeneous origin and must be regarded as 

 derivations of the San Jorge sea-bottom. The lithologic 

 character of the northern half then depends in a great 

 measure on the nature of the earlier Jurassic and Creta- 

 ceous continental surface. The facies of limestones with 



