ORIGIN OF THE ANDES 
17 
are unknown geologically; they reach altitudes of about 5,000 
feet and some writers consider them a part of the Andean system. 
Faunal and floral evidences suggest that they were formerly 
(i. e. in post-Miocene time) higher, and formed a link between the 
Andes and the mountains of Darien. The three Colombian chains 
converge toward the Ecuador frontier and form the so-called knot 
of Imbabura, and from here to the so-called Loja knot on the 
Peruvian frontier the Ecuadorian Andes form a double chain 
(Oriental and Occidental) trending, rather closely to each other, 
south by west, and forming a single system united by transverse 
paramos which divide the inter-Andine area into the basins of 
Quito (9,500 feet), Ambato (8,500 feet), Cuenca (7,800 feet) 
and Loja (7,200 feet). 
The peaks reach well above the snow-line, about 16,000 feet. 
Many of them are volcanic. None of the enclosed basins are low 
enough to be in the subtropical faunal or floral zones. Ecuador 
also has a Coast Range trending northwesterly from Guayaquil 
which is reported to be composed of Mesozoic sediments and 
prophyritic eruptions like those of the Northwestern Range, of 
which it may be a spur. Little is yet known of the geology of the 
Ecuadorian ranges. I should expect it to be similar to that of 
the Colombian ranges. 
The tectonics around the Loja basin are but little understood. 
The Rio Zamora which drains it into the Maranon lies in a deep 
valley, south of which the Western Andes, or Maritime Cordillera 
continue southward, west of the valley of the Maranon (the Cor¬ 
dillera Negra of Peruvian authors). East of the Maranon are 
the more lofty snow-clad Cordillera Blanca, which extend from 
the great bend of the Maranon southward to where they join 
the main western chain at the knot of Cerro de Pasco, in latitude 
10° 30' south. Farther to the east, in northern Peru, and 
forming the divide between the Huallaga and Ucayali, is another 
range, little known and variously correlated. From the knot of 
Cerro de Pasco south to the knot of Vilcanoto, or Cuzco (Lat. 14° 
30'), the system has a breadth of about 250 miles and the ranges 
are sometimes grouped as Western, Central and Eastern. All 
but the Western, in which the passes are two or three thousand feet 
higher than in the more Eastern Range, are illy defined and much 
broken with narrow, high valleys and punos. 
In southern Peru the Western, or Maritime, Cordillera is well ' 
