252 ANNALS NEW YORK ACADEMY OF SCIENCES 



At some points along the eastern slope, the escarpment is of such a char- 

 acter as to suggest faulting on a very large scale. 



Continuing across the Intercordilleran Belt, consisting of an undu- 

 lating plain, some 3,000 to 4,000 feet below the summits of the West 

 Cordillera, we find the formations involved in its structure to be sand- 

 stones, shales and limestones, through which, at various points, knobs of 

 volcanic rock have pushed their way and now form a part, at least, of the 

 principal relief of the Cerro de Pasco lowland. The town of Cerro de 

 Pasco is built on the slope of one of these knobs. Here we find a mass 

 of volcanic rock in contact with a large body of limestone. It is on or 

 near the contact that the famous ore body is located. Going northward 

 over the intercordilleran lowland to Goyllarisquisca we again encounter 

 coal-bearing formations. Just what are the stratigraphieal relations be- 

 tween these and the coal-bearing measures of Ututo and Cajatambo is 

 not known. Beyond this point the writer has not penetrated the wilds 

 of the East Cordillera. From data obtained from prospectors and en- 

 gineers, I have reason to believe that the principal formations involved in 

 its structure are very much older than any we have seen in the West 

 Cordillera. Probably Devonian and Silurian and older terranes asso- 

 ciated with a huge mass of intrusives make up the great part of the East 

 Eange. By way of comparison, I may add that the formations found in 

 the Lima- Oroya section duplicate, in the main, the Huacho section, both 

 in succession and kind. Oro}^a stands at the south end of the Cerro de 

 Pasco lowland. Here we have the expected limestones and shales and 

 .associated intrusives noted to the north. 



Ocona-Cora Puno Section. — Starting at Ocona, we meet first of all the 

 outliers within the limits of the coastal plain, or the Cadena de la Costa. 

 Ascending the shoreward escarpment, we pass over the ridge and on to 

 the edge of the enormous pampa which we already know under the name 

 of Cuno cuno and have recognized as an intergral part of the Coastal 

 Plain province. Should we pass into the canyon of the Ocona, we should 

 see the Tertiary sediments resting unconformably upon a series of sand- 

 stones and shales. Inland along the line of our proposed section, the 

 Tertiary sediments give way to the development of an enormous mud 

 flow, which, on the inner edge, or escarpment overlooking the valleys of 

 the Chorunga and Ocona, is not far from 1,000 feet in thickness. Tn 

 the canyon of the Ocona, in the region of Piuca, the pre-Tertiary sedi- 

 ments recognized nearer the coast have been largely replaced by various 

 types of volcanics. There are at least three types to be found in the 

 Ocona and Chorunga valleys, namely, a dioritic, a trachytic and a basaltic 

 type. Their succession of volcanic activity was probably in the order 



