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 low and have been built up on broad and thick sheets of lava. Those on the west are high and have been built up on a lower basement of lava.

On the earlier maps of the Puna de Atacama the mountains were represented as scattered peaks, and the intervening spaces appeared as broad plateaus. The true character of the Puna is quite different. It consists of mountain chains, knots, and isolated peaks arranged along dominating north-south lines as in the sketch, Figure 87. West of the Nevado de Cachi which forms the eastern wall is a line of salinas or salars. These become larger toward the west. The Salina de Anto- falla is 90 miles long, though but 2 to 6 miles wide. North of it is the Salina de Arizaro, the largest salar of the Puna de Atacama, 25 by 55 miles in extent; and others continue the line still farther north.

Westward of the first line of salars, which includes the Salina de Pastos Grandes, is a north-south line of peaks of lesser height and much less definition than is shown by the Nevado de Cachi. There follows a second line of salars represented by Quiron and Rincon. West of this line we come to a very important topographic feature, the Cordillera de Callalaste. Though the height of this cordillera is not great—its peaks range from 5000 to 5600 meters—yet to the west of it we have the largest salars, the most desolate country, the most inac- cessible portion of the Puna de Atacama, a region practically uninhabited. East of the Cordillera Callalaste and its continua- tion to the south, the Sierra Famatina, are better conditions with more fresh water, a larger number of aguadas and vegas, an increase in the number of settlements, and a moderation of the hard conditions that prevail in the upper Puna. The basins are more extensive, and the drainage features better developed, with a number of principal streams that break through narrow gorges and give outlet to the Argentine plain. The group of settlements in the basin of Fiambala, the gather- ing of waters at Antofagasta de la Sierra, and the settlements