was no moon, and the darknesscame rapidly down to make the going still more difficult. At thesummitof every rise the guides would look about for the light at Matilla, and presently they located it. It is set up in a wooden tower to guide the night traveler, who would otherwise be lost in the maze of ravines. By three in the morning we reached the floor of the Quebrada de Quisma opposite Matilla, but in the darkness we could not find the ford, and, fearful of the river sands, the guides thought it best to make camp there. We set fire to a dry bush and by its light, as that of a huge torch, prepared a meal and staked out the mules. (For illustration of Matilla see Frontispiece.) The next morning we found the ford but a hundred yards away, crossed over to Matilla, and rode on to Pica where we spent the day. Here we obtained additional blankets, brought in regular trade from Bolivia by llama caravan, and added to our stock of provisions. The next day took us across the drifted sand tracts east of Pica (Fig. 4) and to the wells at Tambillo, the last outpost of the desert in the Andean foothills.
Water Supply of the Oases
The village of Matilla is supported by a thin thread of water that issues from the so-called mountains far above, the Altos de Picea, They are really a plateau and part of an even surface that extends for thirty or forty miles along the Andean crest. Halfway up their slopes one comes upon the edge of a belt of grass that denotes a rainfall slightly heavier and, of still more importance, regular in occurrence. It is a mid-mountain belt of annual rains and permanent pasture. Almost before we had time to note the first spears of grass at about 8000 feet we also noted the first bird calls we had heard since we left the coast with its bewildering millions of sea fowl. <A little higher and we came to an old and now abandoned corral and camp site where the mountain shepherds from the eastern, or Bolivian, side of the Andes had camped in traveling down to the desert towns and ports or had pastured their llamas for a time. From out this zone of grassland several streams run to converge in the Quebrada de Quisma where Matilla lies.
