of the Cuzco Valley,, Peru. 43 



cirque lias the appearance of a crater and has doubtless given 

 rise to the erroneous belief that Cerro Picol is volcanic. 



Bedrock about the headwaters of Rio Huaccoto and extending 

 north to Cerro Atasccasa is almost completely cloaked with 

 glacial debris. Eight moraines, 500 to 3,000 feet in length, 

 were noted along the borders of flat-floored, smooth, grass- 

 covered valleys leading southward to the edge of rock-walled 

 canyons. Striated bowlders attaining diameters of 4 feet and 

 more, plucked from ledges of igneous and sedimentary rocks, 

 strew the surface. Within an area of about 6 square miles the 

 till is very unevenly spread; depressions between interlocking 

 moraines are common, small lakes and swamps occur, and no 

 definite lines of drainage have yet been established. 20 



Glacial features of large variety and unusual freshness are 

 displayed in the region drained by the Chchiraura. North of 

 the tiny group of herdsmen's cottages known as Ccasa-Cancha 

 the stream consists of two branches which surround the igneous 

 mass of Ichchu-Orcco. The western branch rises in a swamp 

 whose basin has been overdeepened by ice. It has the typical 

 features of a glaciated valley and is bordered in part by banks 

 of morainal material and in part by rock walls. Exposed 

 ledges of andesite are scoured and striated on both horizontal 

 and vertical surfaces. Erratics are abundant on divides at 

 13,500 feet and are found to a small extent at 13,000 feet and 

 below. The terminal moraine has been almost completely 

 removed. The south branch of the Chchiraura rises in a rock- 

 walled cirque nearly square in ground plan, perched high on the 

 flank of Pachatucsa, 14,500 to 15,500 feet above sea level. The 

 floor of the cirque dips to the south at an angle of 20° and 

 descends by giant steps with scoured treads from the inner 

 edges of which huge blocks have been removed and carried 

 to lower levels. Patches of ground moraine and irregular 

 masses of marginal moraines are distributed over the bare rock 

 floor at the mouth of the cirque, and the base of the slope at 

 13,500 feet is plastered with a mass of till, the remnants of 

 the youngest of a series of terminal moraines. 



Below the lip of the cirque the valley extends as a wide, 

 smooth-floored, flat trough bordered by walls which rise steeply 

 to heights exceeding 400 feet (fig. 27). The gradient of the 

 floor is scarcely sufficient to carry the stream, which, beginning 

 as a swamp, meanders through boggy flats, passes two recessional 

 moraines, and finally emerges from the lowest moraine as 

 20 See p. 15. 



