Page:The fairy tales of science.djvu/287

 The deep valleys that radiate from the central mass of a great mountain are invariably filled with frozen water, and are the outlets of the frozen snowfields, or in the words of a clever writer, "the glacier is a river of ice, and the névé its source." Glaciers sometimes fill up a valley twenty miles long by three or four broad to the depth of six hundred feet. Although apparently solid and stationary, they really move slowly down the valley, and carry with them, either on the surface, frozen into their mass, or grinding and rubbing along the bottom, all the fragments, large and small, from blocks many tons in weight, down to the finest sand and mud, that rain, and ice, and the friction of the moving glacier itself, detach from the adjacent rocks. The glaciers of the Alps, and probably those of other regions, descend to a vertical depth of nearly 4000 feet below the line of perpetual snow, and into a climate much warmer than that of our own island, before they finally melt away, and leap forth as rivers of running water. The heap of materials of all sorts and sizes which they deposit at their melting extremity is called the moraine, a term which is also applied to the lines of blocks that are being carried along on the surface of the glacier, the floating sticks and straws of the solid river. Strange to say, the simple fact of the motion of glaciers was not admitted until a comparatively recent date, though it was well known that the