28 



II. E. Gregory — A 'Geologic Reconnaissance 



Valleys. 



Huaianay Y alley. — The history of the drainage of the Cuzco 

 region can not be written from the facts disclosed by existing 

 field studies. The solution of the problem involves a knowledge 

 of crustal movements and structural relations throughout 

 southern Peru. If the view of the regional physiography 

 presented in this paper 11 is accepted, the larger drainage fea- 

 tures are readily interpreted; the TTrubamba and Apurimac 



Fig. 18. 



RIO PARPAY 

 14 OOO 



YUCAY-PAMPA CATUNGA-MACHU 

 14000 



W.ofS. 



E.of N. 



Fig. IS. Cross profile, Cuzco Valley, drawn through the city of Cuzco. 



were established on the Inca peneplain and their down-trench- 

 ing is the result of general uplift ; the Pucara and other streams 

 entering Lake Titicaca have found a temporary base-level on 

 the floor of a down-faulted interior basin. If the regional 

 slopes were followed the Huatanay should flow westward to 

 join its master stream, and it is not improbable that during 

 the peneplain cycle the waters from the Cuzco area found their 









Fig. 19. 







RIOHUACO PUNCO 



SAN 3E.RONIMO 



CERR0 1 PICOL 



I4,ooo -. 





RIO HUATANAY 





- 1-4,000 



13.000 - 







ii 





- 13,000 



12,000 - 







^^-^ 





- 12,000 



1 1 , OOO - 





-^— — E — -^^ 





- 11,000 









O 2. MILES 



l> 



J. 



Fig. 19. Cross profile, Cuzco Valley, drawn through San Geronimo. 



way to the Amazon through the Ttica-Ttica Pass, whose fea- 

 tures as an old-age valley are well marked. The regional uplift 

 of the Andean region was, however, accompanied by warping, 

 by profound and widespread faulting, and doubtless also by 

 the intrusion of igneous rock. The normal course of many 



11 See p. 17. 



