232 ANNALS NEW YORE ACADEMY OF SCIENCES 



many of these partially filled pre-Tertiary valleys the recent deposits of 

 sand, gravel and clay have again been attacked by the present streams and 

 redistributed at lower levels. The same type of physiographic history is 

 repeated in the valleys of the Eimac and the Chillon. The lower part of 

 the Eimac Valley and the broad area where it is confluent with the 

 Chillon have been aggraded by the deposition of an enormous sheet of 

 fluviatile material. Lima, the capital of the republic, stands on the edge 

 of this fluviatile plain. Whether Tertiary formations exist beneath the 

 sheet of waste or not has not yet been determined. 



Not until we reach the vicinity of Cerro Azul, Cahete and Chincha 

 does the typical coastal plain again make its appearance. In the section 

 through Chincha it has a width of some three or four kilometers. The 

 transverse streams have incised themselves but slightly into the surface 

 deposits. The formations thus far exposed here appear to be post-Ter- 

 tiary waste, sands and conglomerates, undoubtedly deposited upon late 

 Tertiary clays. The latter may be seen in sections at points between 

 Chincha and Pisco to the south. These are regarded as the equivalents 

 of the late Tertiary clays at the bottom of the Paita section. Folding 

 and minute faulting may be seen at various points; the best exposures 

 occur near Pisco. To the north of Pisco, the amount of Tertiary deposi- 

 tion may have been very considerable, but to the south, there is reason to 

 believe that no great proportions were reached. The fact that a verj 

 large part of the shoreward area from Paracas to the mouth of the Eiver 

 lea is occupied by outliers of the pre-Tertiary oldland, precludes, at least, 

 the idea of Tertiary deposition on any great scale in that particular sec- 

 tion. It was only between this broken line of hills or outliers and foot- 

 hills of the west range that any great amount of Tertiary deposits accu- 

 mulated. In the upper part of the lea Valley, within the limits of the 

 coastal plain, a very thick sheet of post-Tertiary waste was spread out on 

 the lea plains as far south as Ocacaje. To the west of Ocacaje, the best 

 exposures of the light-colored Tertiary clays containing fossil fish are 

 to be seen. These rest upon the eastern flank of the outliers already 

 referred to and probably pass under the fluviatile plains in the upper 

 stretches of the lea Valley and plains. From Ocacaje south we may trace 

 the plain across the Pampa de Huayuri to Palpa, San Jose and Nasca. 

 To the south of the Eio Grande, we reach the Pampas de Yunga Colo- 

 rado and Bella Union on the northwest side of the Valley of Acari. Thp 

 plain finally ends at a point a short distance south of the mouth of the 

 Eiver Yauca. The Pampas de Yunga are separated from the coast line 

 by Cerro Yunga, composed of pre-Tertiary formations, another outlier of 

 the West Eange. Some distance to the south of Cerro Yunga, the coastal 



