We wondered how long ago our mountain was an active volcano. To-day, less than two hundred miles south of here are live peaks, like El Misti and Ubinas, which still smolder occasionally and have been known in the memory of man to give forth great showers of cinders covering a wide area. Possibly not so very long ago the great truncated peak of Coropuna was formed by a last flickering of the ancient fires. Dr. Bowman says that the greater part of the vast accumulation of lavas and volcanic cinders in this vicinity goes far back to a period preceding the last glacial epoch. The enormous amount of erosion that has taken place in the adjacent canyons and the great numbers of strata, composed of lava flows, laid bare by the mighty streams of the glacial period all point to this conclusion. My saddle mule was one of those cantankerous beasts that are gentle enough as long as they are allowed to have their own way. In her case this meant that she was happy only when going along close to her friends in the caravan. If reined in, while I took some notes, she became very restive, finally whirling around, plunging and kicking. Contrariwise, no amount of spurring or lashing with a stout quirt availed to make her go ahead of her comrades. This morning I was particularly anxious to get a picture of our pack train jogging steadily along over the desert, directly away from Coropuna. Since my mule would not gallop ahead, I had to dismount, run a couple of hundred yards ahead of the rapidly advancing animals and take the picture before they reached me. We were now at an elevation of 16,000 feet above sea level. Yet to my surprise and delight I found that it was relatively as easy to run here as anywhere, so accustomed had my lungs and heart become to very rarefied air. Had I attempted such a strenuous feat at a similar altitude before climbing Coropuna it would have been physically impossible. Any one who has tried to run two hundred yards at three miles above sea level will understand. We were still in a very arid region; mostly coarse black sand and pebbles, with typical desert shrubs and occasional bunches of tough grass. The slopes of Mt. Solimana on our left were fairly well covered with sparse vegetation. Among the bushes we saw a number of vicuñas, the smallest wild camels of the New World. We tried in vain to get near enough for a photograph. They were extremely timid and scampered away before we were within three hundred yards.