I made several excursions on the glaciers of Mus-tagh-ata on foot or on yaks. One must be well shod so as not to slip, and one must look out for crevasses. Once we were stopped by a crevasse several yards broad and forty-five feet deep. When we stooped over the brim and looked down, it had the appearance of a dark-blue grotto with walls of polished glass, and long icicles hung down from the edges. Streamlets of melted ice run over the surface of the glacier, sometimes flowing quietly and gently as oil in the greenish-blue ice channels, sometimes murmuring in lively leaps. The water can be heard trickling and bubbling at the bottom of the crevasses, and the surface brooks often form fine waterfalls which disappear into chasms of ice. On warm days when the sun shines, thawing proceeds everywhere, and the water trickles, bubbles, and runs all about the ice. But if the weather is dull, cold, and raw, the glaciers are quieter, and when winter comes with its severe cold they are quite hard and still, and the brooks freeze into ice. The yaks of the Kirghizes are wonderfully sure-footed, and one can ride on them over slippery hillocky ice where a man could not possibly walk. The yak thrusts down his hoofs so that the white powdered ice spurts up around him, and if the slope is so steep that he cannot get foothold, he stretches out all four legs and holds them stiff and rigid as iron and thus slides down without tumbling. Sometimes I rode over moraine heaps of huge granite blocks piled one upon another. Then I had to take a firm grip with my knees, for the yak springs and jumps about like a lunatic.