THE SALAMANCA FORMATION 15 
we found no fossils. The contact with the Patagonian 
was unconformable, 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 Rio Seheun. 
In layer 8 we found large quantities of gypsum, occur- 
ring mostly in balls of radiate structure. Layer II 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 
