254 



THE ANDES OF SOUTHERN PERU 



the small amount of marginal dissection, and the excellent expo- 

 sures made possible by the deep erosion and desert climate, the 

 Majes Valley is one of the most profitable places in Peru for 

 physiographic and geologic study. 



The most complete succession of strata (Tertiary) occurs just 

 below Cantas on the trail to Jaguey (Fig. 171). Upon a floor of 

 granite-gneiss, and alternating beds of quartzite and shale belong- 



COAST RANGE 



COASTAL DESERT 



MARITIME CORDILIERA 



LAVA PLATEAU <~^ VOLCANOES" 



VALLEY FLOOR AT TIME OF GREATEST UPLIFT AND DISSECTION 



BASEMENT SEOIMEHTARIES 

 WITH GRANITE INTRUSIONS 



Fig. 171 — Generalized sketch section to show the structural relations of the Mari- 

 time Cordillera, the desert pampas, and the Coast Range. 



ing to an older series, are deposited heavy beds of red sandstone 

 with many conglomerate lenses. The sandstone strata are meas- 

 urably deformed and their upper surfaces moderately dissected. 

 Upon them have been deposited unconformably a thicker series 

 of deposits, conglomerates, sandstones, and finer wind-blown ma- 

 terial. The basal conglomerate is very coarse — much like beach 

 material in both structure and composition, and similar to that 

 along and south of the present coast at Camana. Higher in the 

 section the material is prevailingly sandy and is deposited in 

 regular beds from a few inches to a few feet in thickness. Near 

 the top of the section are a few hundred feet of strata chiefly wind 

 deposited. Unconformably overlying the whole series and in 

 sharp contrast to the fine wind-blown stuff below it, is a third 

 series of coarse deposits about five hundred feet thick. The top- 

 most material, that forming the surface of the desert upland, con- 

 sists of wind-blown sand now shifted by the wind and gathered 

 into sand dunes or irregular drifts, banks of white earth, "tierra 

 blanca, ' ' and a pebble pavement a few inches thick. 



If the main facts of the above section are now summarized 

 they will facilitate an understanding of other sections about to be 

 described, inasmuch as the summary will in a measure anticipate 



