1 6 THE DESEADO FORMATION OF PATAGONIA 



designated as a Deseado exposure; and it has the same 

 general appearance and color which is found in the green 

 sands of the Deseado pocket on the Rio Chico. However 

 it is conformable interbedded with the underlying and over- 

 lying marine beds and I consider it a part of the marine 

 series. Above it come more white sandy clays that are 

 characteristic of the most of the section. 



Wilckens takes all of this series, from the base of the 

 Salamanca, up to the unconformity below the Patagonian, 

 and makes of it his St. George Period, a transgression 

 epoch, lasting to the end of the Upper Cretaceous. I be- 

 lieve it is all marine, and is all a part of the Upper Creta- 

 ceous transgression of the sea over Patagonia. However 

 the Salamanca is a clear cut deposit and I feel it should 

 be retained as a distinct horizon. The overlying light 

 colored (white, grey, brown, yellow, or green) sandy clay 

 shales represent a deeper water and later fades, which is 

 characteristically developed on the Gulf of St. George, 

 and may well be distinguished as the St. George epoch or 

 series, but I should use the term only in this more limited 

 way. It is the same series which Ameghino has plotted as 

 the Notostylops beds on his section of the coast of Patago- 

 nia. This last it certainly is not. 



The unconformity between these white (or light) sandy 

 clays and the Patagonian represents a regression period, 

 during which Patagonia was not only above water, but 

 extended an unknown distance further to the East. 



It was during this interval of time between the Upper 

 Cretaceous and the Lower Miocene (Patagonian) that the 

 limited and local land deposits known as Casamayor 

 ( = Notostylops), the Astraponotus, and the Deseado ( = 

 Pyrotherium) and probably other beds were laid down. 

 In each case the age must be determined for the individual 

 bed by its contents mostly; for as far as I know none of 

 them overlap anywhere. 



