The Alps. Sir William Martin Conway

sun (whose dissolving power is as operative in the regions so-called of perpetual snow as it is below) percolates into the crevices of the rocks and finds out all their weak places. At night this water freezes, and in freezing expands, thus acting like a wedge and splitting the rock it has penetrated. Next time the sun shines the pieces thus split off may fall. Sooner or later, after repeated operations of the wedge, they must fall, and a new surface of rock will be uncovered to be split and shivered in its turn. The rocks that fall tumble ultimately on to the snow-fields that spread over the high open spaces, where they are taken charge of by the great carrying agents of the heights—the glaciers. The higher a peak is, relatively to its neighbours, the more rapidly will frost attack it, and the more energetic will be the destruction wrought upon it. I have heard it estimated, or perhaps only guessed, that 1000 tons of rock fall daily from the upper portion of the Matterhorn's rock-pyramid. The great peaks of the Himalaya are falling yet more rapidly to pieces.

      But what in this relation is the action of the glaciers? At one time they were regarded as a great abrading agency. It was thought that the high valleys were fashioned out by them. Later it was concluded that their hollowing action was a negligible quantity. The general belief now is that it is not considerable. Whatever may be the action of glaciers upon their beds, it is at all events a small matter compared with their action as transporting agents. Glaciers are not hoary accumulations of snow, collected in hollow places since the beginning of the world, as our forefathers supposed, but flowing streams of ice, whose rate of movement varies with the slope, the latitude, the mean temperature, and other factors of their situation. The snow that falls at high elevations lies in great masses where it finds lodgment, or falls to such places from the steep rocks which are unable to give it steady support. By these means it falls and drifts together into those great upper reservoirs we call the snow-fields—resplendent areas of purest white, so toilsome to cross when the sun shines hotly upon them, and so incomparably beautiful to look upon. Here by melting of the surface, percolation into the body of the snow-field, and freezing there, and by the pressure of the ever-increasing accumulation of snow, the substance is gradually changed into granulated ice, and the ice thus formed slowly moves down-hill. The various neighbouring streams of ice flow and unite together, and thus, reaching lower and lower levels and continually melting, they come to a line where the annual increment of snow is equal in amount to the depth of snow annually melted. This is called the snow-line. Still downward flows the mass, and now the amount melted becomes greater than the amount annually received. The thickness of the ice steadily diminishes till at last the total arrival melts and the glacier ends in a so-called snout.