[Illustration: FIG. 163--Geologic sketch section to show the relation of the volcanic flows of Fig. 164 to the sandstones and quartzites beneath.]
It is noteworthy that the farther east the Carboniferous extends the more dominantly marine it becomes, though marine beds of great thickness constitute a large part of the series in whatever 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 crowning the western border of the Cordillera. Along the line of traverse opportunity was not afforded for further study of this aspect of the series, since our route led generally along the strike rather than along the dip of the beds. It is interesting to note, however, that these observations as to the increasing amounts of clastic material in a westward direction were afterwards confirmed by Señor José Bravo, the Director of the Bureau of Mines at Lima, who had found Carboniferous land plants in shales at Pacasmayo, the only fossils of their kind found in Peru. Formerly it had been supposed that non-marine Carboniferous was not represented in Peru. From the varied nature of the flora, the great thickness of the shales in which the specimens were collected, and the fact that the dominantly marine Carboniferous elsewhere in Peru is of great extent, it is concluded that the land upon which the plants grew had a considerable area and probably extended far west of the present coast line. Since its emergence it has passed through several orogenic movements. These have resulted in the uplift of the marine portion of the Carboniferous, while the terrestrial deposits seem to have all but disappeared in the down-sunken blocks of the ocean floor, west of the great fault developed along the margin of the Cordillera. The following figures are graphic representations of this hypothesis.
[Illustration: FIG. 164--Geologic sketch map and section, Antabamba region. The Antabamba River has cut through almost the entire series of bedded strata].