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 along the mountain flanks into central Chile. On page 246 I have described its appearance and altitude in the neighbor- hood of San Pedro de Atacama and Soncor where we crossed it again in 1913. It is a feature of the mountains that has all sorts of interesting effects upon the local life, fixing the position of many mountain trails and determining the summer pastur- ing grounds of the mountain Indians. This last feature is more and more highly developed as we go southward, for the winters of the mountains on the southern edge of Atacama are pro- gressively more severe, and the grazing folk can use the moun- tain pastures for a part of the year only.

The last part of the ascent to the summit of the western- most plateau-like block of the Andes steepens, and the trail follows now the rocky interfluve, all sand having been blown away, and now a steep-walled quebrada or ravine with a bouldery floor. With increasing altitude (to 14,000 feet) the going in the stecpening trail becomes more and more arduous, and it is with a keen sense of appreciation that one sees the siguo del camino, or pile of stones that marks the sum- mit. Each traveler adds a stone for good luck, and thus in the course of generations the pile has grown to the dimensions shown in Figure 6. The feature is encountered in many places in different forms. Sometimes it is a cross, sometimes a pretentious structure serving as a shrine (Figs. 7 and 8).

After crossing the Altos de Pica, a broad plateau of erosion now uplifted to the great height of 14,000 feet and partly covered with an overflow of lava, we dropped down a steep trail toward Lake Huasco and made camp beside the spring at the western edge of the basin. There was plenty of tola about, and with this and the droppings of the Hamas that had been herded in a stone corral at the camp site we made a camp- fire and spent a comfortable night except for the effects of the altitude. I had first felt its effects at 10,000 feet, but they wore off quickly; whereas my companion, Mr. Rogers, felt them not at all until we had reached 13,000 feet when he became alarm- ingly ill. The next morning he was about as usual and had almost no return of the symptoms during the rest of the journey.