Boundary in South America. 49 



between the Patagonian continental platform and the 

 structural elements to the north. These are the events 

 that characterize the Cretaceous-Tertiary boundary. 

 They are manifested by the hiatus between the San Jorge 

 and its base. If any sediments should be correlated with 

 this epoch, the upper part of the dinosaur-bearing 

 Pahuenche-Beds and their lacustrine and brackish for- 

 mations could perhaps be regarded as contemporaneous. 

 Further, the freshwater beds of Lonquimay, first 

 described by Burckhardt, 121 again recently by Felsch, 122 

 may have been deposited in this period. All these events 

 are approximately contemporaneous with the highest 

 part of the Cretaceous (Danian) and the lowest part of 

 the Paleocene, perhaps the whole Paleocene. The 

 Puerco Beds in New Mexico, the Lance in Wyoming and 

 the Hell Creek Beds in Montana might be correlated with 

 them. Then, the San Jorge-transgression coincides with 

 the Upper Paleocene or with the Lower Eocene and has 

 to be parallelized with the Libyan Formation, the London 

 Clay or the Kirthar Group of India. We have recog- 

 nized that this period was followed by one of regional 

 denudation, which — although lasting only a short time — 

 would, however, require a part of the Eocene, perhaps 

 the whole Eocene. The Casamayor and Deseado (Noto- 

 stylops and Pyrotherium) would then come into the 

 Oligocene. This determination agrees not only with the 

 ideas of Loomis and other competent paleontologists 

 about the age of the Deseado fauna; but a series of 

 geologic and physiographic phenomena would also har- 

 monize. The Patagonian Formation, that unconforma- 

 bly follows upon these strata, remains in the Lower 

 Miocene, where the studies of Ortmann fixed it, a long 

 time ago. 



Future investigations may produce some small dis- 

 placements in this scheme, but they will not affect the 

 result that the San Jorge has to be regarded in a dias- 

 trophic as well as in a paleontological sense as a forerun- 

 ner of the Patagonian Formation. The San Jorge marks 

 in Patagonia the beginning of the Tertiary era. It is a 

 link similar in importance to the two other Tertiary 

 transgressions, the Patagonian and the Parana. 



121 Coupe geologique de la Cordillere entre Las Lajas et Curaeautin, Anales 

 Museo La Plata, Secc. Geologica etc., 3, pp. 43 etc., La Plata, 1900. 



122 Las pizarras bituminosas de Lonquimay, Boletin Sociedad Nac. de 

 Miiieria, No. 220, 32, November and December, 1915. (3) vol. 27, Santiago 

 de Chile. 



Am. Jour. Sci. — Fourth Series, Vol. XLV, No. 265. — January, 1918. 

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