In the glacial valleys, such as Yosemite, Tehipite, and Hetch Hetchy, where young rivers drop from the headlands in long streaming falls, the noise of them contending with the wind makes mimic thunder. Immense curtains of falling water are tossed this way and that, they are caught up and suspended in mid-air, and let fall crashing to the lower levels. When the wind blows straight up the cañon they will rear against it, and leap out a shining arc, shattering in mid-air like bursting bombs of spray. But later in the season, when the streams are heavy with the melting snows, the wind itself is shattered by the weight of falling water--it exhausts itself in obscuring clouds of silver dust. When from Whitney or Williamson or King's Mountain you can see half-a-hundred such young rivers roaring to the morning, it is as beautiful and as terrifying as the sight of youth to timorous age. They go leaping with their shining shields, and their shouting shakes the rocks. Neither you nor they believe that the most and the best they will come to is an irrigating canal between sober rows of prunes and barley. Higher than the forests, or the waters rising out of them, is the _Py-weack_, the Land of Shining Rocks. They shine with glacier polish; horses on the high trails sniff suspiciously at their glittering surfaces. Time can lay slight hold on them by thunder, by frost, and the little grey moss; it has not yet subdued the front of Oppapago. Here between snowless ribs and buttresses are the shrunken glaciers that feed the streams, little toy models of the ancient rivers of ice. The snowfields of the Sierras are not so inconsiderable as they seem: they are dwarfed by the precipices among which they hide. Inaccessible to ordinary mountain travel, they make their best showing from the surrounding plains, where, lifted in the middle air, they glow with ethereal whiteness. Close by they display a bewildering waste of broken ice, boulders, and crevasses, made bleaker by the cobalt shadows. [Illustration: MOUNT SHASTA--SIERRA GLOW] North the line of peaks stretches, broken by the passes that give access to the west. Between them, above the source of streams, in the ice-gouged hollows, lie unfathomable waters that take all their life from the sky. Or perhaps they are reservoirs from which the sky is made, fluid jade and azulite and hyacinth and chrysoprase, as if the skies of many days had run their colours in those bleak bowls. For at this altitude the wave contour of the range comes out most sharply; the sky is strangely deep and darker, as if through its translucence one glimpsed the void of space. One sees the moon and the planets wandering there with pale lamps held aloft.