PHYSIOGRAPHIC AND GEOLOGIC DEVELOPMENT 253 



from view below the sediments of either the Pleistocene or the 

 present river gravels. In the more central parts of the depres- 

 sion occupied by the Urubamba Valley, only knobs or ridges pro- 

 ject here and there above the general level. 



The Coastal Tertiary 



The Tertiary deposits of the Peruvian desert region southwest 

 of the Andes have many special features related to coastal de- 

 formation, changes of climate, and great Andean uplifts. They 

 lie between the west coast of Peru at Camana and the high, lava- 

 covered country that forms the western border of the Andes and 

 in places are over a mile thick. They are non-fossiliferous, cross- 

 bedded, ripple-marked, and have abundant lenses of conglomerate 

 of all sizes. The beds rest upon an irregular floor developed upon 

 a varied mass of rocks. In some places the basement consists of 

 old strata, strongly deformed and eroded. In other places it con- 

 sists of a granite allied in character and probably in origin with 

 the old granite-gneiss of the Coast Range toward the west. Else- 

 where the rock is lava, evidently the earliest in the great series 

 of volcanic flows that form this portion of the Andes. 



The deposits on the western border of the Andes are excel- 

 lently exposed in the Majes Valley, one of the most famous in 

 Peru, though its fame rests rather upon the excellence and abun- 

 dance of its vineyards and wines than its splendid geologic sec- 

 tions. Its head lies near the base of the snow-capped peaks of 

 Coropuna ; its mouth is at Camana on the Pacific, a hundred miles 

 north of Mollendo. It is both narrow and deep; one may ride 

 across its floor anywhere in a half hour. In places it is a narrow 

 canyon. Above Cantas it is sunk nearly a mile below the level of 

 the desert upland through which it flows. Along its borders are 

 exposed basal granites, old sedimentaries, and lavas ; inter-bedded 

 with it are other lavas that lie near the base of the great volcanic 

 series; through it still project the old granites of the Coast 

 Range; and upon it have been accumulated additional volcanic 

 rocks, wind-blown deposits, and, finally, coarse wash formed dur- 

 ing the glacial period. From both the variety of the formations, 



