THE SALAMANCA FORMATION 15 



we found no fossils. The contact with the Patagonian 

 was unconformahle, in some places being 50 feet higher 

 than in others near by. 



In section A the typical Salamanca is below sea level, 

 and the lower parts of the section are made up of the white 

 sandy clay shales, so typical all along the Gulf of St. George. 

 In the midst of these clays at the level indicated as 2 oc- 

 curred a layer of concretions. On breaking these we found 

 two specimens of Nautilus valencienni H., clear evidence 

 that they were of marine origin. Layer 5 was filled with 

 hundreds of the very characteristic oyster, described as 

 Ostrea (Gryphaea) pyrotheriorum. Though in earlier 

 papers suggesting that O. pyrotheriorum represented a 

 horizon of marine sediments corresponding in age to the 

 Deseado ( = Pyrotherium) formation, in his Formations 

 Sedimentaires, Ameghino places this fossil in the Sala- 

 manca fauna, though it here occurs at least 275 feet above 

 the typical Salamanca fauna. I believe the layer should 

 be distinguished. It is later than the typical Salamanca, 

 though belonging to the same transgression of the sea over 

 Patagonia. In layer 7 we found still another marine fauna 

 consisting of 



Ostrea guarantica H. 



Venericardia sp. 



Corbula sp. 



Aporrhais. 



Patomides. 



Oxyrhinca. 



Milobates. 



Fragments of the limbs of a crab in abundance. 



This seems to be the same fauna as that described by 

 Ameghino as the Sehuen developed on the RioSeheun. 



In layer 8 we found large quantities of gypsum, occur- 

 ring mostly in balls of radiate structure. Layer n was a 

 coarse green sand, and in it we found some fragments of 

 some sort of a bone. I think this layer is what Ameghino 



