30 Windhausen — The Cretaceous-Tertiary 



tion to the Salamanca-fauna. On the basis of analogous 

 observations in the Rio Negro-valley, I assume the exist- 

 ence of an hiatus in the Loomis-sections, separating 

 marine Salamanca from terrestrial Notostylops Beds. I 

 suppose, this hiatus in section A lies above the layer 7 

 and in section B above the layer 4, corresponding to a 

 peneplain of widespread distribution; the same pene- 

 plain has also been found in the neighborhood of General 

 Roca. It cuts the sediments of the San Jorge obliquely 

 to its different levels. ' 



The lithogic character of the Salamanca in the sections 

 of Loomis is determined by sandy clays and green slates 

 and limestones with the known fauna. A connected 

 sequence of strata cannot be obtained from the two sec- 

 tions, because the peneplain cuts different levels and the 

 basement is not visible. Furthermore, a somewhat 

 irregular sedimentation is a characteristic feature of 

 near-shore deposits, and to these also belong the Sala- 

 manca Beds in the surroundings of the Gulf of St. 

 George. In case A, a complex of about 200 and in case 

 B, of about 120 feet in thickness can be observed. It is 

 interesting that Ostrea guaranitica has been found by 

 Loomis in those places, a few feet above the Ostrea pyro- 

 theriorum. In this way, further evidence is given for 

 the equivalence and contemporaneity of the so-called 

 Sehueneen with Roca and Salamanca Beds. 



The Notostylops and Pyrotherium Beds (Casamayor 

 and Deseado) in the sections of Loomis consist of alter- 

 nating yellow gypsum-bearing clays, green cross-bedded 

 sands and coarse sandstones with opalized wood. In 

 contrast to Roca the volcanic component has been greatly 

 reduced. To a large extent these terrestrial deposits 

 may doubtless be considered as accumulations in depres- 

 sions and troughs, but nevertheless they are deposits of 

 a widespread distribution corresponding to a general 

 period of accumulation. It seems to me that Carlos 

 Ameghino (loc. cit.) is right in laying stress on this lat- 

 ter fact. Such a surprising abundance of fossil remains 

 as in the Deseado exposure of Loomis is an exceptional 

 case, but the same formation with scarcer or without any 

 organic remains is spread over a large area in Pata- 

 gonia. Just as the peneplain above the Salamanca indi- 

 cates a denudation period of general character, it is 

 necessary to assign a regional character to the period of 

 accumulation which is represented by the alleged terres- 

 trial deposits. 



