After leaving Uaiculi the way lay along the edge of the barren plain for some miles. A ridge of high peaks, some of them covered with snow, rises on each side. Then the trail ascended the slope to the east, rising gradually in a series of terraces, four to six hundred feet high. Sometimes low hills flanked the trail, and often we passed along the top of flat plateaus. The slopes of the highest peaks were littered with fields of broken sandstone that resembled a quarry-dump for shattered rocks of large size; groves of gnarled trees, not over twenty-five feet high, grew in these rock-strewn areas, and we found them nowhere else. Where there were no rocks thick clumps of tall grass stood. When we reached the elevation of thirteen thousand four hundred and fifty feet we found a very peculiar plant belonging to the bromelias (_Puya_); the smooth, trunk-like stem was about eighteen inches through; this served as a pedestal for the dense clump of slender, bayonet-like leaves; a tall spike of small yellow flowers rose from the centre of the plant. Numbers of giant humming-birds (_Patagona gigas_) came to sip nectar from these flowers. [Illustration: The great _Puya_, a species of pine growing in the Bolivian Andes at an elevation of 13,000 feet.] The mountains seem formed of solid sandstone. Here and there a ledge, worn and rounded by the elements, projects conspicuously and resembles an impregnable fort or castle of majestic though fantastic design. We reached a lone Indian hut late at night, and, while the _arriero_ was loath to halt, the mules were too tired to go much farther. The neighborhood was in bad repute on account of a number of robberies and murders that had recently taken place there, and not long after our arrival we saw mysterious signal-fires spring up on the surrounding slopes. We therefore camped in a corral, the enclosing stone walls serving as a barricade, and alternately did sentry duty throughout the night. I believe one of the reasons for our being left severely alone was that each member of the expedition was advised to display casually his pistol to the inhabitants of the hut, and to acquaint them with its possibilities. This same ruse has prevented serious trouble in a number of instances. I have found that by far in the greater part of South America there is not the slightest necessity of carrying a weapon of any kind; but there are isolated regions where the moral effect on the natives produced by wearing a revolver of generous size in a conspicuous place is so great that one may tread with impunity what would otherwise be dangerous ground.