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 it forms a protection against the wind. There is a small com- merce in cactus, the sole wood for construction of floors, benches, tables, etc. The best pastures for the sheep are found on the flanks of the cordillera; only mules, asses, and llamas can subsist upon the grasses of the high plateau except in quite special situations, as, for instance, at the vegas or ciénegas, the naturally irrigated spots where there is more grass than usual. In the great stretch of country that forms the western half of the Puna the shepherds do not come at all, and it is not until one reaches an elevation of 14,400 feet on the western range that signs of their occupation are found.

Of agriculture there is very little in the Puna: alfalfa and barley in special places; potatoes, quinoa, and habas, or beans. Corn is produced in valleys protected from the wind, and both cobs and corn have been found in pre-Hispanic graves and in fields and terraces now in ruins on the borders of the Punade Jujuy, showing that the plant had been cultivated on a great scale and indicating either that the climate has changed since that period or that the inhabitants of the Puna de Jujuy in pre- Hispanic times imported some of their provisions of corn from lower lands or from San Pedro de Atacama across the Puna, which was then inhabited by people of the same stock. Horses cannot live upon the high plateau; only mules and asses and flocks of sheep and llamas constitute the basis of wealth. The mineral industry of the Puna is almost abandoned today because of the high cost of transport; it employs llareta as fuel for steam,

In spite of the severe climate of the Puna, three mails a month are maintained between Salta and San Pedro de Ata- cama over a distance of 300 miles (480 kilometers). The mail carriers relay the mails and arrange the relays in such a man- ner as to travel both day and night, thus covering this great distance in six days. Sometimes the mail, like the cattle driving, is held up for two weeks by deep snows.