of the Cuzco Valley, Peru. 39 



ice final down-cutting of the outlet and removal of the accumu- 

 lated lake sediments began, a process continuing to the present 

 time. 



Lake Morkill is one of a number of ancient fresh-water 

 bodies occupying depressions in the Inca peneplain of southern 

 Peru which await investigation. The only one heretofore 

 studied presents features closely similar to those found in the 

 Cuzco Basin. 14 



Glaciation. 



Introduction. 



The position of the present snow line in southern Peru 

 has been determined for only a few places. Even less is known 

 regarding the position of existing glaciers and of the moraines 

 formed in Pleistocene time. Extreme views are held by 

 Hautkal, 15 who expressed the opinion that no general Pleisto- 

 cene glaciation occurred in Peru, and by Duehas, 16 who con- 

 sidered the Cuzco Valley at elevations of 11,000 feet and below 

 to have been occupied by ice. Adams 17 placed the lower limit 

 of glaciers in the Poto region of southern Peru at 2,500 feet 

 above the ice fields of the glacial periods. 



No glaciers exist within the drainage basin of the Cuzco 

 Valley, and no perennial accumulations of snow are to be found 

 even at an elevation of 15,915 feet, the culminating point on 

 the valley rim, but snow rests on the highest summits well into 

 summer. After showers Picol and Pachatusca and Seneca 

 may be mantled with snow during the warmest months, and 

 on rare occasions the lower slopes and even the floor of the 

 valley are coated with white late in the spring and early in 

 autumn. During the glacial period all the higher peaks and 

 ridges were snow-capped and tongues of ice occupied the heads 

 of many valleys tributary to the Huatanay. The lowest 

 undoubted deposits resulting directly from ice action stand at 

 approximately 12,500 feet. Several well-developed moraines 

 were mapped at 13,000 feet, and the valley profiles at this 

 elevation indicate the presence of ice. Above 13,500 feet the 

 landscape at all points has been molded by ancient glaciers and 



14 Gregory, H. E., Geologic reconnaissance of the Ayusbamba (Peru) 

 fossil beds; this Journal, xxxvii, 125-140, 1914. 



15 Quatare Vergletschernng der Anden in Bolivien und Peru, Zeitschr. 

 fur Gletscherkunde, i, p. 203, 1906. 



16 Duenas, op. cit., 1907. 



17 An outline review of the geology of Peru, Smithsonian Inst. Report 

 for 1908, p. 409. 



