THE PERUVIAN LANDSCAPE 197 



rated by well-defined "Cordilleras." The plateau divisions are 

 not everywhere of the same origin. Those southwest of Cuzco 

 (Fig. 130), and in the Anta Basin (Fig. 124), northwest of Cuzco, 

 are due to prolonged erosion and may be defined as peneplane 

 surfaces uplifted to a great height. They are now bordered on 

 the one hand by deep valleys and troughs and basins of erosion 

 and deformation; and, on the other hand, by residual elevations 

 that owe their present topography to glacial erosion superim- 

 posed upon the normal erosion of the peneplane cycle. The 

 residuals form true mountain chains like the Cordillera Vilcanota 

 and Cordillera Vilcapampa; the depressions due to erosion or 

 deformation or both are either basins like those of Anta and 

 Cuzco or valleys of the canyon type like the Urubamba canyon; 

 the plateaus are broad rolling surfaces, the punas of the Peruvian 

 Andes. 



There are two other types of plateaus. The one represents a 

 mature stage in the erosion cycle instead of an ultimate stage ; the 

 other is volcanic in origin. The former is best developed about 

 Antabamba (Figs. 122 and 123), where again deep canyons and 

 residual ranges form the borders of the plateau remnants. The 

 latter is well developed above Cotahuasi and in its simplest form 

 is represented in Fig. 133. Its surface is the top of a vast accumu- 

 lation of lavas in places over a mile thick. While rough in detail 

 it is astonishingly smooth in a broad view (Fig. 29). Above it 

 rise two types of elevations : first, isolated volcanic cones of great 

 extent surrounded by huge lava flows of considerable relief; and 

 second, discontinuous lines of peaks where volcanic cones of less 

 extent are crowded closely together. The former type is displayed 

 on the Coropuna Quadrangle, the latter on the Cotahuasi and La 

 Cumbre Quadrangles. 



So high is the elevation of the lava plateau, so porous its. soil, 

 so dry the climate, that a few through-flowing streams gather the 

 drainage of a vast territory and, as in the Grand Canyon country 

 of our West, they have at long intervals cut profound canyons. 

 The Anna has cut a deep gorge at Salamanca ; the Cotahuasi runs 

 in a canyon in places 7,000 feet deep ; the Majes heads at the edge 



