134 H. E. Gregory — Geologic Reconnaissance of the 



steeper gradient, — a course leading south directly to the Apuri- 

 mac, — is being established by headward erosion, and the divide 

 has migrated eastward within recent times (fig. 7). 



Dissection of the lacustrine beds has been accomplished by 

 Calvo brook,* consisting of two streams which unite to form 

 the main outlet channel. The valley of Calvo brook presents 

 youthful features both along its larger branches and in the 

 innumerable tiny canyons cut in clays and sands. About 

 one-third of the interstream spaces consists of imperfectly 



Fig. 7. 



Fig. 7. View of fossil locality, looking southwestward across the divide 

 between Calvo brook and tbe Apuriinac river. The divide is migrating 

 toward Calvo brook. Photograph by G. F. Eaton. 



drained grass plats ; the remaining portion is marked by " bad 

 land" slopes and mounds cut by canyons 30-40 feet deep, two 

 to ten feet wide, producing a surface difficult to traverse. 

 Surficial erosion is augmented by numerous springs and seeps, 

 emerging at the contact of clay and sand. Landslides are of 

 frequent occurrence and greatly facilitate the removal of the 

 lacustrine deposits. Ancient corrals and andenes point to for- 

 mer human occupation, and their position shows that a consid- 

 erable part of the tillable land has been lost through recent 

 stream erosion. 



* The liberty has been taken of naming this stream in honor of Senor Eme- 

 terio Calvo, the hospitable proprietor of hacienda Ayusbamba. 



