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 in the latitude in which this change occurs. The Sillilica trail hits both Lake Huasco, as I have described, and also a group of smaller basins between it and the central salt pan of western Bolivia at Llica. Huasco was at one time filled with water almost to the point of overflowing; and one after another of the neighboring mountain basins had the same fate in the Ice Age, when a wetter climate turned these now shallow grass- bordered evaporating pans into deep lakes filled almost to their brims.

After three uneventful days of journeying across the high mountain belt in which we passed only a few tiny settlements of a few huts each (a principal one is called Cueva Negra), we arrived at Llica on the eastern edge of the mountains in Bolivia (12,000 feet). We entered the town late at night after riding into a bitter wind that blew off the cold salars lying just east of the village. The mules floundered in the morass at the edge of the salar that here skirts the mountain border, and we should have had a cheerless camp indeed but for the happy coming of a Bolivian shepherd who had returned from his mountain camp in time to guide us by a narrow course to the end of the principal street of the village. The place was quite dark, not a single light showing anywhere. The clatter of our pack train awoke dogs and villagers, for the coming of a stranger after nightfall is a most unusual event in this remote place. At length we reached a sort of public place where we obtained lodging in a small room that had first been cleared of pigs and chickens and then swept. Tea and eggs and such bread, hard as a rock, as we had carried from Lagunas in the nitrate desert formed our supper. The next day we rode north along the shore line that here stands out prominently along the mountain side and out over the salar a short distance to study the composition of its surface. Then we talked with the single merchant of the town about the llama caravans and pack trains that come here, the source of food—the life here is al- most exclusively pastoral—and the ways of the mountain folk who live in these secluded valleys.