244 



THE ANDES OF SOUTHERN PERU 



C D 



Fig. 163 — Geologic sketch section to 

 show the relation of the volcanic flows 

 of Fig. 164 to the sandstones and quart- 

 zites beneath. 



The degree of deformation of the Carboniferous sediments 

 varies between simple uplift through moderate folding and com- 

 plex disturbances resulting in nearly vertical attitudes. The sim- 

 plest structures are represented at Pasaje, where the uplift of the 



intruded schists, marginal to 

 the Vilcapampa batholith, has 

 produced an enormous mono- 

 clinal fold exposing the entire 

 section from basal conglomer- 

 ates and sandstones to the 

 thickest limestone. Above Chu- 

 quibambilla the limestones have 

 been uplifted and very gently folded by the invasion of granite as- 

 sociated with the main batholith and several satellitic batholiths of 

 limited extent. A higher degree of complexity is shown at Pampa- 

 conas (Fig. 141), where the main monoclinal fold is traversed al- 

 most at right angles by secondary folds of great amplitude. The 

 limestones are there carried to the limit of the winter snows almost 

 at the summit of the Cordillera. The crest of each secondary anti- 

 cline rises to form a group of conspicuous peaks and tabular 

 ridges. Higher in the section, as at Puquiura, the sandstones are 

 thrown into a series of huge anticlines and synclines, apparently 

 by the marginal compression brought about at the time of the in- 

 trusion of the granite core of the range. At Pongo de Mainique 

 the whole of the visible Carboniferous is practically vertical, and 

 is cut off by a great fault marking the abrupt eastern border of 

 the Cordillera. 



It is noteworthy that the farther east the Carboniferous ex- 

 tends the more dominantly marine it becomes, though marine beds 

 of great thickness constitute a large part of the series in what- 

 ever location. From Huascatay westward the limestones become 

 more and more argillaceous, and finally give way altogether to an 

 enormous thickness of shales, sandstones, and thin conglomerates. 

 These were observed to extend with strong inclination westward 

 out of the region studied and into and under the volcanoes crown- 

 ing the western border of the Cordillera. Along the line of 



