HAIL, SNOW, AND GLACIERS. 109 The crevasses gradually disappear below the cause of disturbance, the fractures rejoining by a process called regelation. Regelation is the property which fragments of moist ice have of becoming firmly cemented together, when their surfaces are brought into contact under pressure. The water derived from the melting of the ice issues from a cavernous arch at the end of the glacier. The volume of the issuing stream, which is often considerable, is dependent on the tempera- ture, being greater during the warm months of the year. Many rivers have their origin in these glacier streams; as, the Rhone and the Rhine, in Europe, and the Ganges, in Asia. The distance the glacier extends below the snow line depends on the mass and velocity of the ice, and the rapidity with which it is melted. When the winter snows are light, and the following sum- mer unusually warm, the end of the glacier re- treats up the mountain. On the contrary, heavy snowfalls in winter, followed by a cool summer, permit the end of the glacier to advance far into the valley below. 285. Transporting Power of Glaciers.— All along the borders of the valleys, stones and dirt roll down the declivities, and, accumulating on the surface of the moving mass, are carried with it to a lower level. These accumulations of dirt and stones are called moraines; they are most sharply marked at the sides of the glaciers, where they are called dateral moraines. Where two gla- ciers flow into one common valley a moraine called the medial moraine marks the junction of their * meeting edges. At the end of the glacier, a ter- minal moraine extends in a wide curve across the vailey. Medial moraines are sometimes over a hundred feet in height. Terminal moraines some- times attain the height of several hundred feet. The masses of stone transported by glaciers are often of great size. Some have been found 100 feet long, 50 feet wide, and 40 feet high. 286, Erosion.—Such immense masses of ice must deepen considerably the valleys through which they move. When they have deserted their former valleys, evidences of their previous existence are to be found in the long lines of unstratified rocks and mud left by their moraines and boulders, and especially in the deep grooves, or scratches, cut in the bottom or sides of the valleys by rocks imbedded in the moving ice mass. These scratches are parallel, and show the direction of the motion. The water which issues from the terminal cave is deeply charged with a fine sediment, the result.of erosion. This sediment is exceedingly fertile, and, spread out by the rivers on the flood-grounds, becomes a source of agricul- tural wealth. ~ Fiords and Glacial Lakes.—Valleys cut by glaciers are characterized by parallel sides. Gla- cial valleys, when formed on mountains that slope down to the ocean, if the region is subjected to subsequent depression and the valleys partially submerged, are penetrated by the sea, and form arms of the sea extending far into the mountains. Such valleys are called fiords. The following are the most important fiord regions : (1.) On the coasts of Norway. (2.) On the western coasts of the Dominion of Canada and Alaska. (8.) On the coasts of Greenland, where the valleys are still covered with ice masses. The numerous lakes of glacial regions owe their origin either to the erosion of softer rocks, or to the damming up of rivers by the terminal mo- raines left by a retreating glacier. 287. Geographical Distribution of Glaciers.— The best known glacial system in the world is found in Europe, in the region of the Central Alps. Here no less than 1100 glaciers are found, one hundred of which are of large size. One of the best known of the European glaciers is that of the Mer de Glace (Sea of Ice). It descends from the slopes of the range of Mont Blanc, and is formed by the confluence of three large glaciers: the Glacier du Géant, the Glacier de Léchaud, and the Glacier du Taléfre. Fig. 97, The Mer de Glace, Glaciers occur also in the Pyrenees Mountains; in the Caucasus range; and in the Scandinavian plateau, from which they descend into the Norwegian fiords to less than 1000 feet from the level of the sea. They also occur in the Patagonian Andes :