50 Windhausen — The Cretaceous- Tertiary 



Thus, the chief result of this paper emphasizes a prin- 

 ciple expressed by Pompeokj 128 in the following words: 

 "The great transgressions did not conquer large areas 

 during a short geologic time-unit, but gradually advanced 

 step by step through several geologic periods." The 

 transgression of the San Jorge leveled the way for 

 the subsequent transgressions. Just as we observe on 

 the western border of this continent, in the region of the 

 great Andine geosyncline, from the Liassic through the 

 Dogger and up into the Tithonic and Lower Cretaceous, 

 a gradual acceleration of the transgressions, an enlarg- 

 ing of areas and an increasing of faunistic wealth, so the 

 importance of Tertiary transgressions increased by 

 degrees. These phenomena manifest a law of rhythmi- 

 cal movements ; but the explanation of the causes of this 

 rhythm is still as obscure as is the great problem of the 

 primitive causes of crustal movements. 



Conclusions. 



1. In Patagonia the Cretaceous and Tertiary are 

 obviously separated by a stratigraphic as well as faun- 

 istic break. 



2. The hiatus at the Cretaceous-Tertiary boundary 

 corresponds to the first phase of the Andine orogenetic 

 movements. These movements in the epirogenetic sense 

 caused the breaking down of the Brazilo-Ethiopian Con- 

 tinent, the formation of the South Atlantic basin and the 

 posthumous reopening of the graben-like depression 

 between the Patagonian continental platform and the 

 structural elements of Central and Northern Argentina. 



3. The formation of the South Atlantic basin opened 

 the way for the Tertiary transgressions spreading over 

 the Patagonian Continent. The San Jorge-Formation 

 must be regarded as the first of these. 



4. The paleogeographic reconstruction of the San 

 Jorge-Sea shows that the shore-lines were in a remark- 

 able manner influenced by ancient structural elements. 

 The northern branch of this sea entered the region of 

 the present mouth of the Rio Negro by way of the graben- 

 like depression at the northern border (fault-scarp) of 

 the Patagonian mass and reached as far as the Rio Atuel. 

 The most southerly deposits of the San Jorge have been 

 observed in the region of the Lago Argentino. 



123 Die Meere der Vorzeit, Gottingen, 1909. 



