32 ANNALS NEW YORK ACADEMY OF SCIENCES 



In conclusion, then, we may say that the age of the fossils of the upper 

 Amazon Valley is not definitely known, and consequently we cannot more 

 than conjecture where the East Andean Sea joined the ocean; 16 but this 

 sea must have extended south and have had a narrow connection with the 

 ocean in the region of either Eio Bermejo, Bio Colorado-Patagonia or the 

 bay of Arica. This connection was perhaps not broken before the Mio- 

 cene, but it Avas broken by the Tertiary rise of the Andes. It is also im- 

 portant to note that no evidence is yet known which indicates that the 

 exit of this sea simultaneously cut east by west both the Archean moun- 

 tains flanking the northeast portion of Patagonia and those on the west- 

 ern side of Patagonia in Chile in such a way as to isolate Patagonia from 

 Brazil. In fact, the evidence at hand is all against such a view. 



REVERSAL OF RIO AMAZONAS 



The following facts indicate that the direction of Rio Amazonas has 

 been reversed: 



1. The Piano Alto which it now traverses has a general southwest dip. 



2. The entire absence of marine Mesozoic and Tertiary fossils in the 

 Piano Alto. 



3. The position of the East Andean Sea. 



4. The Tertiary rise of the Andes. 



5. The general north and south direction of trend lines and the loca- 

 tion of marine deposits in western South America. 



In an interesting treatise on the geology of the lower Amazon, Katzer 

 (1903) concluded that previous to the Miocene the Amazon flowed west 

 from somewhere in the region of Eio Paru. To the east and north of the 

 present mouth of the Amazon, he conceived a vast mass of land which 

 sank beneath the Atlantic Ocean when the Amazon became reversed. 17 



Katzer also states that, during the reversal of the Amazon, a large lake 

 was formed, which extended eastward from Rio Nauta to the original 

 watershed. It appears that he has assumed the formation of this 

 huge lake in order to explain the formation of the fresh-water deposits 

 of Erere. Katzer also maintains that no marine Cretaceous or Tertiary 

 beds exist in the lower Amazon Valley (Pirabas Cretaceous being on the 



10 I am inclined to believe that it extended south along the east base of the Andes into 

 Patagonia, because there is no evidence of an eastern extension, a western over the 

 Andes, a northern into Venezuela. The connection by way of Gran Chaco is very ques- 

 tionable, for I believe the Piano Alto of eastern Bolivia joins the northern extensions of 

 the Cordova Mountains. Hence a southern extension into Patagonia meets no obvious 

 objection. 



17 Pilsbry (1911) has also suggested the same idea in his studies on the distribution 

 of fresh water and land mollusca. It is interesting to note that three individuals work- 

 ing in different fields have quite independently arrived at the same general conclusion. 



