70 Bvlletin American Museum of Natural History. [Vol. XXXVI, 



An Outline of Colombian Topogbaphy. 



Detailed descriptions of Colombian topography, so far as we are familiar 

 with it, are given in the itineraries of our various expeditions and in the 

 characterization of the zones and faunas proposed. The physical, and 

 zoogeography of the country is also presented in the accompanying maps. 

 But at the risk of some repetition, it is proposed to present here an outline 

 of Colombian physiography emphasizing those features which are of special 

 importance in the study of the distribution of its life. 



It should be observed that in Ecuador the Andean system is, faunally, 

 composed of but one range with, consequently, but one Pacific and one 

 Atlantic slope, and one Temperate Zone bordered on each side by the Pa- 

 ramo Zone islands of the higher peaks. But shortly after crossing the 

 Colombian boundary this great range branches into three clearly defined 

 ranges, each one of which is separated from its neighbor by a valley which 

 descends to the Tropical Zone. The Magdalena Valley, lying between the 

 Eastern and Central Andes, is never less than thirty miles in width and, in 

 its lower part, much wider. The Cauca Valley, lying between the Central 

 and Western Andes, from somewhat north of Popayan to north of Cartago 

 has a width of twenty to thirty miles, but in Antioquia it is contracted to 

 the width of the Cauca River from the eastern and western banks of which 

 the Central and Western Andes respectively arise. 



Except in this region, therefore, the three ranges of the Andes in Colom- 

 bia nowhere approach one another, and at no place do their upper life- 

 zones — Subtropical, Temperate, and Paramo — come into contact with the 

 corresponding zone of the neighboring range. 



It should further be noted that all three ranges terminate in the Tropical 

 Zone, the Western and Central in Colombia, the Eastern in Venezuela. 

 It follows, therefore, that their three upper zones end, as it were, in the air; 

 that is, at their most northern part, they have no such connection, through 

 gradual descent of zonal boundaries with increasing south latitude, as, for 

 example, exists between the Temperate Zone in Colombia at from 9500 to 

 12,000 feet, and the Temperate Zone in Argentina at sea-level. 



The Western Andes have no peaks reaching to snow-line, and we know 

 of only four points at which they enter the Temperate Zone, one of which, 

 the ParamUlo, is near the northern end of the range. There appear to be 

 no passes below 4900 feet (Cresta de Gallo, 4924 ft.), the average elevation 

 is approximately 7000 feet, and the summit of the range is therefore usually 

 in the Subtropical Zone. 



The Central Andes have a number of snow-crowned peaks; Paramo 



