Palmer — Notes on the Andes of N. W. Argentina. 319 



slight precipitation at present, and where there must have 

 been considerable precipitation in the moister climates of the 

 glacial period, the mountains show signs of former glaciation. 

 On the eastern aspect there are U-shaped valleys, terminal and 

 lateral moraines, and empty cirques. Farther to the south 

 the Andes bear plenty of snow, due to the combination of 

 somewhat lower temperature and of much greater precipitation. 

 To the north also there is more snow because of the far greater 

 precipitation in the belt of the trade winds than in this dry 

 horse latitude belt of northwestern Argentina and Chile. 



The Lines of Salt Lakes. 



The Salars (or Salinas) of Pastos Grandes, Quiron, Pincon 

 and Lexia lie in a series more or less along a north-south line 

 and constitute the eastern chain of high, interior basins ; while 

 the Salar de Atacama constitutes the main portion of the 

 western chain of basins. There are a number of other such 

 intermontane basins, but only the above were encountered on 

 the route of the expedition. In character they are very 

 similar to the salt basins of the southwest of the United States, 

 such as Death Valley, though at a greater elevation. Long 

 erosion in the enclosed basins of this arid region has concen- 

 trated large deposits of the more soluble salts in their low por- 

 tions. The salts include the usual residues from evaporation, 

 chlorides of sodium, potassium and magnesium, borax, and 

 some sulphates and carbonates. Evaporation is not complete 

 in any of the basins, so that there are central lagoons of brine, 

 surrounded by solid residues from evaporation. The lakes 

 have hard borders with a firm, smooth deposit, the upper sur- 

 face of which looks very much like a good asphalt pavement, 

 and which has the same resilient feel under the mule's hoofs. 

 Around this central area of salt, interspaced with open pools, 

 there is a narrow zone of alluvium permeated with saline 

 matter, and outside this again the salt-free margins of alluvial 

 fans which, with gradients of 3° to 5°, run up to the moun- 

 tains. In addition, the Salars of Pastos Grandes, Quiron and 

 Pincon are partly surrounded by the inclined and dissected 

 strata of an earlier period of basin deposition, separated from 

 the present by dynamic disturbances, which tilted and faulted 

 the deposits already formed and exposed them to erosion. 



These basins vary markedly in size. The Salar de Lexia 

 was the smallest observed, being about six by twelve kilo- 

 meters. The basins of Pastos Grandes, Quiron and Pincon 

 are fifteen to twenty-five kilometers wide by forty to fifty-five 

 long. The basin containing the Salar de Atacama is about 

 fifty by one hundred kilometers. 



