250 ANNALS NEW YORK ACADEMY OF SCIENCES 



clition is maintained throughout the Desert of Sechura and the Despo- 

 blado de Olmos. From Chiclayo and Eten south, we have but a rim of 

 the coastal plain left. It attains considerable proportions in the mouths 

 of the valleys of Pacasmayo, Chicama and Santa Catalina. From a topo- 

 graphical point of view, we have here but a narrow expressionless plain, 

 with its seaward edge rapidly retreating under the attack of the Pacific 

 waves. 



The two prominent points where topographic expression relieves the 

 monotony of the plains are Cerro or Silla de Paita and Cerro de Yllesca. 

 These are, in a word, half buried outliers of the foothills of the "Wesi 

 Cordillera. Similar cerritas may be seen in the broad opening of the 

 Pacasmayo Valley. All these were little islands in a Tertiary sea. 

 They are composed of Cretaceous shales and sandstones which have under- 

 gone metamorphism under the effect of intrusives. 



Chincha-Olmos Plain. — From Chincha to Pisco, we have the same 

 monotonous plain. It is not until we reach Pisco that we find a little 

 topographic relief and this time again associated with the uplift of a 

 series of light gray to cream-colored clays. We need, however, only to go 

 a little distance inland to see a continuation of the pampa in the direc- 

 tion of lea. Should we follow the coast, we should find that a consider- 

 able area is occupied by the outliers of the foothills, but these are quite 

 modest in topographic expression. These pre-Tertiary hills continue to 

 the mouth of the river lea and attain considerable width. 



I wish to turn aside here for a moment to refer to the Peninsula of 

 Paracas, a short distance south of Pisco, since its geology is somewhat 

 unique. Some time ago, coal was found in the cliffs of the peninsula, 

 and a company was formed to exploit the deposits. Examination of 

 the waste brought out of some of the prospects revealed the occurrence of 

 true Carboniferous plants. It is the only locality known to the writer 

 where undoubed Carboniferous and coal-bearing measures occur. So far 

 as my observation goes, the Peninsula of Paracas is by far the most 

 ancient "morro" on the entire coast of Peru. It is my belief that tha 

 formations entering into the remainder of the coastal chain, or Cadena 

 de la Costa, are, geologically, much }^ounger. 



Passing to the other side of the shore ridge of which Paracas is the 

 northwestern extension, we find the lowland facing the actual foothills 

 of the West Cordillera cut into by the lea Eiver. Here we are relieved 

 to find another good section of the same light-colored clays as seen in tbe 

 Pisco section. As soon as we reach the Pampa de Huayuri, we are again 

 greeted by an enormous stretch of high plain, and its monotony is only 

 relieved when we reach the modest canyon cut in it by the Rio Grande. 



