=The Central Cordillera= is the true divide, forming the continental watershed. A single river, the Marañon, breaks through in its lower northern part, while 20 coast streams rising in the Central cut the Maritime range; the East Cordillera is fractured by six Peruvian rivers, the Marañon, Huallaga, Perené, Mantaro, Apurimac, Vilcamayu, and Paucartambo, all but the first being affluents of the Ucayali, which some authorities call a tributary of the Marañon. Oftener these two are said to unite to form the Amazon. =The East Cordillera.= While the Central Cordillera is volcanic in part, the East is of Silurian formation, older and non-volcanic except at the edge of Lake Titicaca. The last, in Bolivia a splendid range, is lower in Peru. It has the high plateau region on the west; east is the Amazon Basin into which its spurs extend for varying distances. The Central and Eastern Andes are connected by a transverse mountain knot at Vilcanota, or Cuzco, while a similar knot occurs at Cerro de Pasco. Farther north the Central Cordillera separates the valleys of the Marañon and the Huallaga, while the eastern Andes is between the latter and the Ucayali. The three ranges are clearly defined much of the way in Peru, and back of Chimbote in the section including the Huailas Valley there are four. THE MONTAÑA The third longitudinal division in Peru, the Trans-Andine, usually referred to as the _montaña_, is the region of subtropical and tropical forest. It is traversed by great rivers, largely navigable. Partly in the sierra country are the Marañon, 600, and the Huallaga, 400 miles long, before their union; 150 miles beyond they are joined by the Ucayali, a great river with a course of 600 miles, more navigable than the other two. These three rivers with their affluents drain the northern and the central part of Peru. The streams of the southern portion are tributary to the Madre de Dios which flows into the Beni, the latter uniting with the Mamoré to form the Madeira. The _montaña_ section, 800 miles from north to south, has a sub-tropical region on the lower slopes of the Andes, the branches of which run out 60 or 80 miles towards the lowlands, and the tropical forests of the latter. In the northern section a considerable district between the Huallaga and the Ucayali rivers, traversed by the Andes, is composed of grassy plains called the Pampa del Sacramento. Some of this northern region is called the _montaña_, having its characteristics, although not east of the East Cordillera. CLIMATE