DISTRIBUTION OF THE FISHES 39 
you can very well identify in many a photograph the region from which it 
has come. Region A, the Northwest, is noteworthy for its recently elevated ter- 
races, outwash plains, or tablazos, and dunes. The Western (B) presents a land 
of immense dry canyons of the Rimac and Santa, with somewhat extensive deltas. 
The Southwest (C) presents upland dunes and lava fields, with volcanic cones, and 
approaching topographic maturity as against the youthful west-central section. 
Part I of this work has dealt with the Coast; we are here dealing with portions 
of the remaining six. 
Throughout most of the north-central region (D) the heights of the cordilleras 
are moderate. The western range forms the continental divide, drops from a 
height near Cerro de Pasco of nearly 20000 feet to the northern passes of SOOO feet, 
soaring again toward the voleanic heights of Ecuador. At the southwestward 
extremity of this region the Maranon has its source in Lake Lauricocha and other 
nearby lakes, at 17000 feet, rapidly traversing its gorge north-northwestward to 
emerge through its water-gap, the Pongo de Manseriche, upon the Amazonian 
plain. The Maranon eastwardly skirts the Central Cordillera, which also trends 
north-northwest from the Cerro de Pasco, reaching elevations of only 15000-16000 
feet, but falling away to 2000 feet to allow the emergence of the river. Next east- 
ward is the Rio Huallaga, which also has its birth on the northern slopes of Cerro 
de Pasco at 14000 feet altitude, traveling northward between the Central and 
Eastern Cordilleras, passing around the end of the latter, as it fades out into the 
plain, to become a tributary of the Maranon in northern Peru. The Eastern Cordil- 
lera falls away rapidly to the north from its 15000-16000 feet at Cerro de Pasco 
to mountains of 8OQ00—LOOOO feet about Hudnuco, then lower to the hills about the 
Pampa de Sacramento. This northern province is mostly one of immense gorges 
with abrupt lofty mountains. As rapidly as the ranges were elevated, the inter- 
cordilleran rivers kept pace with their erosive work, from Cretaceous time to 
the present. 
A similar region is that designated as E, the Central. It also is bounded by 
the Eastern and Western Cordilleras, the latter still the continental divide, at the 
northern extremity bounded by the Nudo de Pasco, at the southern by the Nudo 
de Vileanota. The Western Cordillera remains consistently at elevations 16000 
to 18000 feet or above; the Eastern has here overtaken the Western, often sur- 
passing it in elevation, interposing a barrier of extreme magnitude to the moisture- 
laden winds and to plant and animal distribution. Bowman graphically describes 
the assortment of climates from tropical lowlands to permanent ice-fields (1916). 
At the north of this region the Rio Mantaro, arising on the southern flank of 
the Nudo de Pasco, within the pampa de Junin, flows southeastward to join the 
Apurimac, where with united forces they break through the Central Cordillera. 
The Apurimac, having arisen in Laguna Villafrio, southern Peru, near Cailloma, 
courses northwestward between the Western and Central Cordilleras to the junc- 
tion with the Mantaro. Then known as the Ene, and having penetrated the 
Central Cordillera, it travels between the latter and the Eastern Cordillera in 
search of a weak point in the last barrier toward the Atlantic. Here it is joined 
by the Urubamba which drains all of the southeast section. The high mountains 
