Boundary in South America. 11 



not only the beginning of modern geologic history in this 

 part of South America, but is correlated with vaster 

 diastrophic events. Until now, however, neither the 

 fauna of the Roca Beds in the north nor that of the 

 Salamanca Beds in the south has afforded the data for 

 more closely fixing the age and stratigraphic position of 

 the San Jorge. This formation has thus fluctuated 

 between the Upper Senonian and the Patagonian Forma- 

 tion, the Lower Miocene age of which (determined by 

 Ortmann in 1902) was recently confirmed by the studies 

 of Loomis. 28 Indeed, v. Ihering, 2 " in his description of 

 this fauna, doubted the convenience of correlating the San 

 Jorge either with the Upper Cretaceous or with the 

 Lower Tertiary. 



In the first paleontologic monograph on the Roca Beds, 

 C. Burckhardt tried to establish faunistic relations with 

 the Danian of the Brazilian coast 30 and North Africa, 

 and also with the Arrialoor Group of India. This inter- 

 pretation was not accepted by subsequent writers, 31 

 quite in the degree to which they fail in solving the San 

 Jorge-problem. Thus, we see that this formation with 

 a relatively small and poor fauna has lacked the general 

 paleontologic connection requisite to a more satisfactory 

 establishment of its physical, stratigraphic and biologic 

 conditions. But it seems to me that a better interpreta- 

 tion can now be given to the available facts. 



Ortmann 32 can claim the merit of having pointed out 

 as the most striking feature of the fauna of the Patago- 

 nian Beds the relationship to the marine invertebrate 

 faunae of New Zealand and Australia ; though the theory 

 of a connection of southern continental masses towards 

 the close of Mesozoic time, or at the beginning of the 

 Tertiary, is in a general form a postulate of several 

 zoogeographic systems, and is closely allied to H. v. 

 Ihering's theory of "Archinotis." Ortmann empha- 

 sized the fact that the marine fauna of the Patagonian 

 Beds proves the existence of a vast continental mass, 



28 The Deseado Formation of Patagonia, Amherst, Mass., 1914. 



29 Les mollusques des terrains cretaciques superieures de 1 'Argentine 

 orientale, Anales Museo Nacional de Buenos Aires, (3) 9, pp. 193 etc., 1903. 



sa Ch. A. White, Contribucpes a paleontologia do Brazil, Archivos do 

 Museu Naeional do Rio de Janeiro, vol. 7, 1887. 



31 Apart from various reports of H. v. Ihering, may be mentioned : 

 J. Boehm, tiber Ostreen von General Eoea am Rio Negro, Zeitschr. Deutsch. 

 Geol. Gesellsch., 55, Protokol., p. 71, Berlin, 1903. 



32 Reports of the Princeton Univ. Exped. etc., vol. 4, pp. 310 etc. 



