246 ANNALS NEW YORK ACADEMY OF SCIENCES 



far to the north. It thus maintains a position approximately parallel to 

 the Ucayali throughout a long distance. 



The Cerro de Pasco plain is quite clear as far south as Oroyo. In this 

 part of the plateau we again find a pretty sheet of water, but very much 

 smaller than the inland Titicaca. From this body of water, known as 

 Junin, the drainage, instead of going to the Huallaga, now goes to the 

 southeast, the main line of drainage being the so-called Mantaro. From 

 Oroya to Huancayo, the Mantaro has made a most picturesque valley, on 

 the floor of which are located many prosperous agricultural communities. 

 Ascending the highland in the region of Huancayo, we can see to the east 

 the picturesque Cordillera de Marca Valley, really a part of the East 

 Cordillera, while to the west may be noted the West Eange presenting an 

 almost unbroken front. 



From Huancayo, the Mantaro continues its course to the region of 

 Mayoc, where it breaks through the frontal East Eange and deflects again 

 to the northwest for some distance, but finally elbows its way across the 

 last eastern barrier near Huaribamba and joins the Apurimac. We thus 

 find here another illustration of a pattern of drainage which suggests an 

 adjustment to structure, such as may be seen in mairy other regions the 

 world over. 



Belative to the section between Mayoc, or the first elbow of the Man- 

 taro and the Cuzco-Abancay region, I may add, from data obtained from 

 explorers, that it is apparent that it is a broad highland belt into which 

 the east tributaries of the Apurimac have incised themselves until they 

 have cut the entire section into a veritable labyrinth of canyons. In 

 other words, it is simply a continuation of what we noted to the southeast 

 of Cuzco. 



Casma-Huaraz-Huacaybamba Section. — Let us now look at a section 

 through the northern part of the Department of Ancachs beginning 

 with Casma on the coast and ending at Llata on the Maranon. At 

 Casma., and far to the north and south, the foothills of the west slope 

 form the coast line. The main transverse valleys have been aggraded near 

 the present shore line, but we do not go far to the interior before the flat 

 floors are replaced by steep-sided V-shaped valleys. Here again we have 

 the rapidly descending surface of the West Slope; to the interior, this 

 culminates in the West Eange, which in turn overlooks the valley of the 

 Huaraz. The highest points of the range in this section do not exceed 

 15,000 feet. From an examination of the Eaimondi map, it will be seen 

 that it is well defined throughout a large part of the Department of An- 

 cachs. Note the fact, however, that in the place of the broad plain, as 

 found in the Cerro de Pasco section, occupying the belt between the East 



