THE SNOW LINE— GLACIEES. 21 



to 500 miles in a straight line. In this highland region are found, if not the 

 culminating point of the South American continent, at least the groups of peaks 

 and domes which have the greatest mean altitude. Here rise Illampu and 

 Illimani, both of which exceed 21,000 feet. These giants indicate with sufficient 

 accuracy the central point of the Andean system, and the central points of the 

 northern and southern sections are similarly indicated by the other loftiest sum- 

 mits of America — in Ecuador, Chimborazo, long suj)posed to be the highest moun- 

 tain in the world ; and in the Argentino-Chilian Andes, Aconcagua, which at any 

 rate is the culminating peak of the New "World. Besides these extreme summits, 

 dozens of other crests in Venezuela, in Colombia, and in all the other Pacific 

 states exceed 13,000 feet, an altitude far above the zone of arborescent vegetation. 



Snows and Glaciers. 



The snow-line varies with the latitude ; but, as Whymper asks, what is this 

 line ? Certain completely isolated mountains of the Ecuadorian Andes have no 

 permanent snows at 16,o00 feet ; others, more exposed to the moist winds and less 

 subject to rapid evaporation, remain white throughout the year at an altitude 

 exceeding 14,450 feet. Speaking broadly, the snows descend lower and are more 

 abundant in the eastern highlands facing the trade winds than on the western 

 ranges ; for each summit also the rule holds good, the eastern being more snowy 

 than the western slope.* 



In the equatorial Andes from the Nevada de Santa Marta to the Bolivian 

 uplands the limit of perpetual snows may, in a general way, be said to oscillate 

 between 14,750 and 16,400 feet. By a remarkable contrast, the explanation of 

 which must be sought in the varying proportions of moisture brought by the pre- 

 vailing winds, the snows descend as a rule considerably lower on the domes and 

 cones of Ecuador, that is, on the equinoxial line itself, than on the Bolivian and 

 Argentine mountains, under the southern tropical line, or even within the tem- 

 perate zone. The Sierra de Zenta, which rises to 16,400 feet under the tropic 

 of Capricorn, is never snow-clad in summer, and rarely in winter. 



In the Bolivian Andes Pentland tells us that no perennial snows are met on 

 the western slopes lower than 18,370 feet. The flakes are evaporated as fast as 

 they fall without passing to the liquid state to form running waters. The vapoury 

 cloudlets that are seen during the heat of the day rising above the summit of 

 the mountains are the snows returning in this form to the atmosphere. f But 

 south of this zone of dry winds the line of persistent snows is rapidly lowered by 

 the abundant moisture precipitated by the clouds. In the Magellanic archi- 

 pelago and in Tierra del Fuego the lower limit stands at about 4,900 feet. 



Glaciers have been seen in all the Cordilleras in the tropics exceeding 13,000 

 feet, as, for instance, on the Nevada de Santa Marta, the Sierra de Cocui and the 

 Mesa de Herveo, in Colombia. Humboldt having seen none in the Ecuadorian 

 Andes, either because of the foul weather or because they were covered in some 



* Edward Whymper, Travels amongst the Great Andes of the Equator. 

 t Martin de Moiissy, Confédération Argentine. 



