242 



THE ANDES OF SOUTHERN PERU 



It is succeeded by evenly bedded sandstones of fine and coarse 

 composition in alternate beds, then follow shales and sandstones 

 and finally the enormous beds of limestone that characterize the 

 series. The structure is on the whole relatively simple in this 

 region, the character and attitude of the beds indicating their ac- 

 cumulation in a nearly horizontal position. Since the basal con- 

 glomerate contains only pebbles and stones derived from the sub- 

 jacent schists and does not contain granites like those in the Cor- 

 dillera Vilcapampa batholith on the east it is concluded that the 



batholithic invasion was ac- 

 companied by the compression 

 and tilting of the Carbonifer- 

 ous beds and that the batholith 

 itself is post-Carboniferous. 

 From the ridge summits above 

 Huascatay and in the deep 

 valleys thereabouts the Car- 

 boniferous strata may be seen 

 to extend far toward the west, 

 and also to have great extent 



Fig. 160 — The deformative effects of 

 the granite intrusion of the Cordillera 

 Vilcapampa are here shown as trans- 

 mitted through ancient schists to the 

 overlying conglomerates, sandstones, and 

 limestones of Carboniferous age, in the 

 Apurimac Valley at Pasaje. 



north and south. Because of 

 their dissected, bare, and, therefore, well-exposed condition they 

 present exceptional opportunities for the study of Carboniferous 

 geology in central Peru. 



Carboniferous strata again appear at Puquiura, Vilcapampa, 

 and Pampaconas. They are sharply upturned against the Vilca- 

 pampa batholith and associated volcanic material, chiefly basalt, 

 porphyry, and various tuffs and related breccias. The Carbonifer- 

 ous beds are here more arenaceous, consisting chiefly of alternat- 

 ing beds of sandstone and shale. The lowermost beds, as at 

 Pongo de Mainique, are dominantly marine, fossiliferous lime- 

 stone beds having a thickness estimated to be over two miles. 



From Huascatay westward and southward the Carboniferous 

 is in part displaced by secondary batholiths of granite, in part 

 cut off or crowded aside by igneous intrusions of later date, and 

 in still larger part buried under great masses of Tertiary volcanic 



