Boundary in South America. 43 



Pelecypoda, Gastropoda, corals and Bryozoa may be 

 regarded as a characteristic deposit of the San Jorge. 

 They indicate the culminating phase of the transgression, 

 but prove a very moderate depth. The green sands and 

 soft sandy clays which are quite extensive about the 

 Gulf of St. George indicate a near shore and these 

 deposits might well be called "meeressand." The 

 entire lack of coast conglomerates is explained by the 

 character of the base, which over a large area is com- 

 posed of the Variegated Sandstones of the Upper Creta- 

 ceous. These sandstones almost invariably have a fine 

 or middle grain, and their derivatives were deposited as 

 fine-grained mud and sand on the submarine continental 

 slope. 



Part IV. — Paleontology of the San Jorge-Formation. 



The general faunistic character of the San Jorge has 

 already been dealt with in Part I. A relatively secluded 

 evolution in the South Atlantic and Antarctic regions is 

 the most important factor aiding us to understand the 

 paleontologic position. 



The former interpretation of the San Jorge-fauna was 

 influenced by the indefensible stratigraphic division into 

 various members, really only differences of facies. 

 Further, an unbiased interpretation was rendered very 

 difficult by acceptance of a Cretaceous age. The most 

 peculiar view was maintained by Ameghino who would 

 prove the Cretaceous age of the Patagonian mammal 

 faunas, correlating for this purpose the Roca and Sala- 

 manca with the Middle Cretaceous. The asserted pres- 

 ence of ammonites brought confusion to its culminating 

 point. 



The table of invertebrates found in the San Jorge at 

 different localities, as given in the appendix to this paper, 

 is only of a preliminary character. 102 This table has 

 been drawn up on the basis of all the information con- 

 tained in the bibliography and collections made on vari- 

 ous occasions during recent years. The catalogue of v. 

 Ihering (1914) has also been consulted, as it contains 

 further information about the appearance of certain fos- 

 sils. A few localities, from which Dr. Groeber brought 



102 rpjjg wr ^ er }j as \ n hand a revision of the whole San Jorge-fauna and 

 hopes to publish it soon. 



