MARSTERS, PHYSIOGRAPHY OF THE PERUVIAN ANDES 251 



On the southeast side and close to the coast is the Cerro de Yungi, an- 

 other pre-Tertiary outlier. From this point to the termination of the 

 Chincha-Olmos section we see again just the young Tertiary plain slightly- 

 cut into by the rivers de Acari and Yuaca. 



Ocona-Moquequa Section. — In the southern section, which may be 

 aptly termed the Ocona-Moquequa section, we have a repetition of the 

 same topographic expression and the same formations involved, with oue 

 additional feature, and that is the role played by the mud flows. As 

 already indicated, they form a very large part of the formations entering 

 into the coastal plains extending from the Valley of Caraveli to the 

 Pampa de Clemisi. The special feature of the south section is the per- 

 sistence and strong relief of the coastal chain. It extends practically 

 throughout the entire length of the coast line. I have indicated that 

 the formations entering into the structure of the Cadena de la Costa are 

 the same as appear in the north. While this may be true in some parts,. 

 I am inclined to think that, in the south, other formations than those 

 of the foothills of the cordillera so far noted may be found in the Cadena 

 de la Costa. 



Huacho-Cerro de Pasco Section. — I have already called attention to 

 the occurrence of an evident west slope facing the Pacific Oce?n and the 

 coastal plains. It has a marked inclination towards the sea. It is thor- 

 oughly cut to pieces by a network of transverse valleys. It is only when 

 you ascend the uppermost edges of an}^ of these valleys that this feature- 

 becomes apparent. Nevertheless, above the general sky line of the slope, 

 we can see many elevations. 



The geology of the above section is as follows. Near the coast the 

 formations are sandstones and shales into which have been intruded two> 

 types of volcanics. These are then followed by a broad band of crystal- 

 lines, probably diorites and related types. These are, in turn, followed, 

 by shales and sandstones. Large coal deposits are to be found in this 

 part of the section. The shales and sandstones extend to and beyond 

 Oyon. In the vicinity of Ututo, the sandstones and shales are replaced 

 by an enormous thickness of limestones. Into the limestones and the 

 inner edge of the sandstone and shale formations, enormous volcanic 

 masses of at least two kinds have been thrust. In this section at least, 

 the volcanics form most of the crests of the West Cordillera. The sedi- 

 mentaries, especially in close proximity with the volcanics, have been 

 folded and crushed on a very large scale. 



The eastern slope of the West Cordillera is remarkably well defined. 

 Limestones are here turned up on edge, and adjacent to this horizon we- 

 find the volcanics. Each formation presents its own type of topography ... 



