Boundary in South America. 25 



on the occasion of his investigations in the lower Rio 

 Negro-valley, visited this place (1913) and made a collec- 

 tion of fossils. According to him, the San Jorge is 

 exposed in the bottom of this depression; strata of the 

 Patagonian Formation appear in the slopes of the walls, 

 while above this a second terrace is formed by deposits 

 of the Rio Negro Sandstone. 



The stratigraphy of the so-called Salamanca Beds in 

 the surroundings of the Gulf of St. George is based 

 chiefly upon the various reports of Ameghino and v. 

 Ihering. Besides this several sections have been 

 described in the publications of Stappenbeck 60 and of 

 Loomis 61 and the aforementioned critical study of 

 Wilckens is of much importance. Tournouer 62 issued a 

 detailed stratigraphic study of the occurrence of verte- 

 brates in several places in this district, but he gave less 

 attention to the marine deposits. 



Just as in the region of General Roca, an impartial 

 examination of the stratigraphic conditions in the sur- 

 roundings of the Gulf of St. George will lead to the con- 

 clusion that the Salamanca Beds are a deposit due to a 

 widespread marine transgression, and obviously overlap 

 the Variegated Sandstones of the Upper Cretaceous, or 

 its highest part, the dinosaur-bearing deposits of the 

 Pehuenche Beds. Towards the top these marine Sala- 

 manca Beds are cut by a peneplain and upon this surface 

 have been laid down the terrestrial deposits with Noto- 

 stylops, Astraponotus and Pyrotherium. No more than 

 in Roca are there reasons for assuming in this district 

 an intercalation of these marine sediments In the Varie- 

 gated Sandstones. Ameghino, 63 who described two sec- 

 tions of the southern shore of Lake Colhue Huapi, is 

 inconsistent in this regard. Although the two sections 

 proceed from nearly the same place, in the first one the 

 layer with Ostrea pyrotheriorum has been drawn as a 

 light intercalation, while in the second section the same 

 layer appears as a constant and normally stratified sedi- 

 ment, resting with regularity upon the Pehuenche Beds 



60 Informe preliminar relativo a la parte Sudeste del Territorio del 

 Chubut, Anales Ministerio de Agrieultura, Seceion Geologia etc., vol. 4, 

 No. 1, Buenos Aires, 1909. 



01 The Deseado Formation of Patagonia, 1914. 



62 Note sur la geologie et la paleontologie de la Patagonie, Bull. Soe. 

 Geologique de France, (4), vol. 3, pp. 463 etc., 1903. 



63 Les formations sedimentaires, p. 63, fig. 9 and p. 112, fig. 31. 



