318 Palmer — Notes on the Andes of N. W. Argentina. 



Westward from the Serrarrias de Purilacte to Oalama is a 

 long alluvial slope, fully exposed to the nearly continuous 

 northwest winds of the region. This wind has developed to a 

 very high degree the characteristic desert pavement of wind- 

 polished and facetted pebbles. The only interruption to this 

 long westward sloping expanse of alluvium is a group of knobs 

 of augite andesite at Cerrillos. 



The Maritime Cordillera. 



The Maritime Cordillera, which has been referred to above, 

 consists of a long chain of volcanic peaks with their associated 

 flows of lava. They extend the whole length of the Central 

 Andes region and constitute a lava field, which in size is com- 

 parable with the Columbian field of North America and with 

 the Deccan field of British India. Though the activity of these 

 volcanoes began in the Tertiary, there are some which are still 

 feebly active. Smoke and steam issue from some, and the 

 Franciscan monks of Salta tell of finding human implements 

 and remains in the lavas near Antofagasta de la Sierra. 



One contrasting point regarding the Eastern and Maritime 

 Cordilleras is that of the relative heights of their peaks and 

 passes. In the Eastern Cordillera the passes range from 5000 

 to 5400 meters (16,000 to 17,500 feet), but the peaks run only 

 a small amount higher, that is, to 5500 or 6000 meters (18,000 

 or 20,000 feet). The passes have not been cut down very 

 much, and the mountains are in extreme youth, or rather in 

 the early stages of erosion in a new cycle. In the Maritime 

 Cordillera, on the other hand, the passes are lower, averaging 

 about 4600 meters (15,000 feet), but the peaks run up to 6000 

 meters (20,000 feet) and even to 7000 meters (23,000 feet). 

 This is due to the fact that they are volcanic cones 1500 to 

 2500 meters (5000 to 8000 feet) high, built on a rather level 

 surface at about 3600 meters (12,000 feet) above sea level. 



Glaciation. 



Though the mountains of the Maritime or Western Cor- 

 dillera reach as a maximum an altitude of four and a quarter 

 miles, they have suffered only slight glaciation. What glaciers 

 there are now are but little more than snow banks on the tops 

 of the very highest peaks. This absence of glaciation is due 

 to the combination of extreme aridity and the comparatively 

 high temperature of the region near the Tropic of Capricorn, 

 the two factors sufficing to overcome the effect of these veiw 

 high altitudes. In the Eastern Cordillera, where there is a 



