50 



II. E. Gregory — A Geologic Reconnaissance 



about the Cuzco Basin now undertook to destroy their previous 

 work. Degradation, heretofore active on the upper slopes, 

 was extended to the lower slopes, and aggradation was halted 

 even on the valley floor. The time elapsing since this change 



Fig. 31. 



.;-;;;": ^, 



Fig. 31. Wall of canyon, 100 feet deep in lacustrine deposits, one mile 

 north of San Sebastian. 



in stream habit has not been sufficient to remove all waste from 

 the lower slopes and to redistribute the piedmont materials, 

 but the work already accomplished is large in amount. All 

 tributaries to the Huatanay have partly re-excavated their 



