236 THE ANDES OF SOUTHERN PERU 



peated uplifts of the earth's crust reformed the ancient chains or 

 created new ones out of the rock waste derived from them. Each 

 new set of forms, therefore, exhibits some features transmitted 

 from the past. Indeed, the landscape of today is like the human 

 race — inheriting much of its character from past generations. 

 For this reason the philosophical study of topographic forms re- 

 quires at least a broad knowledge of related geologic structures. 



SCHISTS AND SILURIAN" SLATES x 



The oldest series of rocks along the seventy-third meridian of 

 Peru extends eastward from the Vilcapampa batholith nearly to 

 the border of the Cordillera, Fig. 157. It consists of (1) a great 

 mass of slates and shales with remarkable uniformity of composi- 

 tion and structure over great areas, and (2) older schists and 

 siliceous members in restricted belts. They are everywhere thor- 

 oughly jointed; near the batholith they are also mineralized and 

 altered from their original condition; in a few places they have 

 been intruded with dikes and other form of igneous rock. 



The slates and shales underlie known Carboniferous strata on 

 their eastern border and appear to be a physical continuation of 

 the fossiliferous slates of Bolivia; hence they are provisionally 

 referred to the Silurian, though they may possibly be Devonian. 

 Certainly the known Devonian exceeds in extent the known 

 Silurian in the Central Andes but its lithological character is 

 generally quite unlike the character of the slates here referred to 

 the Silurian. The schists are of great but unknown age. They 

 are unconformably overlain by known Carboniferous at Puquiura 

 in the Vilcapampa Valley (Fig. 158), and near Chuquibambilla on 

 the opposite side of the Cordillera Vilcapampa. The deeply 

 weathered fissile mica schists east of Pasaje (see Appendix C for 

 all locations) are also unconformably overlain by conglomerate 

 and sandstone of Carboniferous age. While the schists vary con- 

 siderably in lithological appearance and also in structure, they are 

 everywhere the lowest rocks in the series and may with confidence 



1 For a list of the fossils that form the basis of the age determinations in this 

 chapter see Appendix B. 



