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 range from 11,300 to 14,100 feet; mean maximum temperature, 21.4° C. (70.5° F.); mean minimum, —0.5° (31.1° F.); mean 10.4° C. (50.7° F.); mean humidity, 37.5 per cent. Violent rains of short duration, with thunder and lightning, fall only during three summer months of December, January, and February. During the rest of the year the atmospheric humidity is be- tween 50 and 65 per cent. While there are no weather sta- tions in the Puna, all of the official records from scattered stations in the country roundabout show very meager pre- cipitation: Humahuaca (latitude 23°10") has 155 mm.; Ca- fayate, in the Calchaqui valley (26°), 377 mm.; Santa Maria (26°45"}, 180 mm.; Tinogasta (27°50’), 110 mm. In these and other stations in the Andean Zone go per cent of the rain falls from October to March.

The Puna would be impossible to cross if the climate were less dry, for the great elevation of the country would turn the winter moisture into snow and deeply blanket the entire region. The contrast between the cold of the Puna de Atacama and that of the bordering valleys was increased during our journcy by the fact that in the earlier days at the border of the moun- tains we had most delightful weather, somewhat like our “Indian Summer” and called by the natives after the feast of St. John (June 24), El Verano de San Juan. The guides were in great haste to reach the point on the trail where they could see the active volcano Lascar, near the pass in the westernmost chain. If the mountain is quiet they cross leisurely; when it smokes they hurry the mules, saying that the weather will be bad. So intensely cold is the winter season that the shepherds migrate from the higher pastures of the mountains to the warmer lower valleys that lie in the edge of the pampa or be- tween the lesser ranges of the cordillera. Even at the lower elevation of 8000 feet near Tambillo, close to the edge of the great Salar de Atacama, the temperature fell on the night of our stay (June 29-30) to 5° F. (-15° C.) at 6 A.M., after a daytime temperature of 88° F. (31° C.) at 2 P.M., or a range of 53° F. (46° C.) in eight hours! The locality is not far from the end