THE ANDES 19 



explains the feebleness of the erosion by water and 

 the extent of the erosion by wind. 



It is aridity, too, that gives their particular character 

 to the Argentine Andes. They have little trace of 

 perpetual snow, the lower limit of which approaches 

 to within about four miles of the Bolivian frontier. 

 There are no glaciers there ; they reappear in the south 

 only in the latitude of San Juan and Mendoza, on the 

 flanks of the three giants of the southern Cordillera, 

 Mercedario, Aconcagua, and Tupungato. Below the 

 small number of steep furrows which the glaciers have 

 carved, and usually up to the top of the mountain, 

 there spreads what has been called, very expressively, 

 " the zone of rubbish." In this the winter's snows, 

 fretted by the sun in that clear atmosphere, form those 

 multitudes of narrow pyramids which the Argentinians 

 compare to processions of white-robed pilgrims. The 

 underlying rock is rarely visible. It is covered with 

 a thick cloak of rubbish, split off by the frost, which 

 the slow-moving waters released by the melting of the 

 snows heap up at the foot of the slopes, at the bottom 

 of depressions. The half-buried summits are succeeded 

 by basins of accumulation. In the valleys round the 

 mountains there are immense beds of detritic, half- 

 rounded shingle. The torrents have cut their way 

 through the alluvial mass, and they flow at the 

 foot of high terraces which mark the sites of former 

 valleys. 



The spread of colonization toward the south during 

 the last generation has extended Argentine territory 

 beyond the limits of these classic scenes. The Patagonian 

 Andes differ profoundly from the Northern Andes ; 

 and the change is not more sudden than that of the 

 climate, to which it is due. Going toward the south, 

 one passes, almost without a break, from the Atlas 

 Mountains to Scandinavia. The moisture increases 

 in proportion as the mean temperature falls. The 

 mountains are covered with snow, and the glaciers 



