6 Windhausen — The Cretaceous-Tertiary 



the west and consequently the formation of the South 

 Atlantic basin. In the same way, it is proven that the 

 claim that ammonites had been found in these beds was 

 utterly unfounded and that these sediments cannot be 

 correlated with the ammonite- and baculite-bearing 

 Senonian sediments of Southern Patagonia (Lago 

 Argentino, Ultima Esperanza etc.). 



Further collections and studies of the sediments of the 

 Roca-Salamanqueano or San Jorge-Formation have con- 

 vinced me that this fauna is to be regarded as the hitherto 

 missing one of the Early Tertiary of the Patagonian and 

 South Atlantic region and that in it we must see the fore- 

 runner of the Patagonian Formation. But the interest 

 offered by this fauna does not end with these facts. In 

 contrast with Chile, where a long denudation period 

 covers the whole time between the Senonian of Quin- 

 quina and the Navidad Beds, we find in Patagonia not 

 only in evidence an Early Tertiary marine fauna, but 

 also a series of continental deposits with terrestrial 

 faunas at the bottom and top of these marine sediments. 

 Thus, the study of the San Jorge is connected with the 

 problem of the stratigraphic position and age of the 

 dinosaur-bearing horizons and the oldest mammal-bear- 

 ing sediments of Patagonia. Furthermore, our present 

 knowledge of this subject will enable us to attempt to 

 reconstruct the limits of the San Jorge-Formation, and 

 connectedly to study a number of general geologic and 

 paleontologic questions of great importance for this part 

 of South America. The San Jorge-Formation and its 

 faunistic, stratigraphic, diastrophic and paleogeographic 

 conditions are a cardinal point in the problem of the 

 Cretaceous-Tertiary boundary in Patagonia. Moreover, 

 a parallelism of geologic history in the north and south 

 of the American Continent is indicated by the terrestrial 

 faunas of this period. In both cases the appearance of 

 placental mammals bears the same relation to the marine 

 sediments. Just as on the Laurentian Continent, on the 

 borders of the retreating Laramie-Sea, so in Argentina, 

 an analogous association of animals can be seen on the 

 borders of the overlapping and invading epicontinental 

 San Jorge-Sea. In both cases, the diastrophic events of 

 special significance are in direct relation to these phenom- 

 ena: in the north there is the great Laramide-revolu- 

 tion, and in the south the orogenetic movements in the 



