. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. 216 THE ANDES OF SOUTHERN PERU EASTERN BORDER RANGES Fig. 142—The deformative effects of the Vilcapampa intrusion on the north- eastern border of the Cordillera. The deformed strata are heavy-bedded sand- stones and shales and the igneous rocks are chiefly granites with bordering porphy- ries. Looking northwest near Puquiura. For conditions near Pampaconas, looking in the opposite direction, see Fig. 141. For conditions on the other side of t
. The Andes of southern Peru; geographical reconnaissance along the seventy-third meridian. Yale Peruvian Expedition (1911); Physical geography; Geology. 216 THE ANDES OF SOUTHERN PERU EASTERN BORDER RANGES Fig. 142—The deformative effects of the Vilcapampa intrusion on the north- eastern border of the Cordillera. The deformed strata are heavy-bedded sand- stones and shales and the igneous rocks are chiefly granites with bordering porphy- ries. Looking northwest near Puquiura. For conditions near Pampaconas, looking in the opposite direction, see Fig. 141. For conditions on the other side of the Cordil- lera see Fig. 140. granite on the one hand and almost unaltered shales and slates on the other. Inclusions or xenoliths of shale are common, however, ten and fifteen miles distant, though they are prominent features in a belt only a few miles wide. The lack of more intense contact effects is a little remarkable in view of the altered character of the inclusions, all of which are crystalline in contrast to the fis- sile shales from which they are chiefly derived. Inclusions with- in a few inches of the border fall into a separate class, since they show in general but trifling alteration and preserve their original cleavage planes. It ap- pears that the depth of the in- trusion must have been rela- tively slight or the intrusion sudden, or both shallow and sudden, conditions which produce a narrow zone of metamorphosed ma- terial and a sharp contact. The relation between shale and granite at Colpani is shown in Fig. 143. Projections of granite extend several feet into the shale and slate and generally end in blunt barbs or knobs. In a few places there is an in- timate mixture of irregular slivers and blocks of crystal- lized sediments in a granitic groundmass, with sharp lines of demarcation between igneous and included material. The contact is vertical for at least several miles. It is probable that other localities on the con- tact exhibit much greater modification
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