MARSTERS, PHYSIOGRAPHY OF THE PERUVIAN ANDES 231 



Valley. The Cerro de Yllesca forms another of those outliers that serve 

 to break the monotony of the sky line as seen from the interior. 



From the Tablazo de Paita, the elevation decreases somewhat in the 

 direction of the Despoblado de Secbura and the Plain of Olmos, while a 

 minimum uplift took place in the section through Morrupe, Chiclayo 

 and Lambeyaque. As to the stratigraphy of the Sechura-Olmos area we 

 can say but little. This is one vast plain, a typical desert, strewn with 

 wind-blown sands, with here and there small depressions occupied with 

 "salinas" or salt deposits, but so slightly dissected that data giving a 

 clue to the stratigraphy are wanting. Sections, however, between the 

 mouth of the Sechura River and Cerro del Yllesca, as exposed on the 

 shore line, lead me to mistrust that beneath the sheet of recent accumula- 

 tions over this vast plain there must exist a thick series of Tertiary sedi- 

 ments. Not a single morro of pre-Tertiary origin is to be found until 

 we approach the region of Olmos. The accumulation of Tertiary sedi- 

 ments in the central parts of the desert may thus be very considerable. 



As has been stated, the continuation of the coastal plain below Cayalti 

 is represented by only a narrow rim, which, as we approach the Valley 

 of Pacasmayo (the Eiver Jequetepeque), again widens out to several kilo- 

 meters. Here we find that the outliers of the foothills are quite numer- 

 ous. An interpretation of the stratigraphy in this valley is difficult on 

 account of the lack of good exposures. Sufficient evidence is at hand 

 to suggest that the red clays corresponding with the lower part of the 

 Paita section are present. 



Following to the south again, but a narrow band of the plain bordering 

 the shore line connects with the Valley of the Chicama and Santa Cata- 

 lina. These valleys are probably filled in part with late Tertiary sedi- 

 ments, but later were littered up with much post-Tertiary waste, a phase 

 of coastal geography to be discussed later. The southern extremity of 

 the northern division ends at Salaverry. 



The stretch of coast from Salaverry south to a point just south of 

 Lima is largely occupied and confronted by the foothills of the Cordil- 

 lera. Only the larger valleys have broad floors near the coast. Whether 

 many of these contain remnants of Tertiary formations or not has not 

 been determined by the writer. It is not improbable that during Tertiary 

 time a fiord-like arm of the Tertiary Sea may have extended into the 

 partially drowned valleys of the West Eange. At all events, it is certain 

 that a large amount of waste has very recently accumulated and spread 

 over the lower stretches near the present shore line, presumably in post- 

 Tertiary time. The valleys of Huacho and Chimbote are fair examples. 

 Mention should also be made of the fact that, in the upper portions of 



