Fig. 166—Geologic sketch map and cross-section in the Cotahuasi Canyon at Cotahuasi. With a slight gap this figure continues Fig. 167 to the left. The section represents a spur of the main plateau about 1,500 feet high in the center of the map.
The Cretaceous limestones of the Cotahuasi Canyon are everywhere greatly and irregularly disturbed. Typical conditions are represented in the maps and sections, Figs. 166 and 167. They are penetrated and tilted by igneous masses, apparently the feeders of the great lava sheets that form the western summit of the Cordillera. From the restricted development of the limestones along a western border zone it might be inferred that they represent a very limited marine invasion. It is certainly clear that great deformative movements were in progress from at least late Palæozoic time since all the Palæozoic deposits are broken abruptly down in this direction, and, except for such isolated occurrences as the land Carboniferous at Pacasmayo, are not found anywhere in the coastal region today. The Cretaceous is not only limited within a relatively narrow shore zone, but also, like the Palæozoic, it is broken down toward the west, not reappearing from beneath the Tertiary cover of the desert region or upon the granite-gneisses that form the foundation for all the known sedimentary strata of the immediate coast.
