gla'shurz, icy masses of great bulk, harder than snow, yet not exactly like common ice, which cover the summits and sides of mountains above the snow line. They are found in Switzerland, Scandinavia, the Andes and in the Rocky Mountains in British Columbia and Alaska. They extend down into the valleys often far below the snow line and bear a considerable resemblance to a frozen torrent. Glaciers have their origin in the higher valleys, where they are formed by the freezing and compression of masses of snow into a granular ice. called by the French neve. The ice of glaciers differs from that produced by the freezing of still water and is composed of thin layers filled with air bubbles. It is likewise more brittle and less transparent. The glaciers are continually moving downward, and not infrequently they reach the borders of cultivation. A glacier moves from eighteen to twenty-four inches in twenty-four hours. At its lower end the glacier is generally very steep and inaccessible. In its middle course it resembles a frozen stream, with an undulating surface, broken up by fissures, or crevasses. As it descends, it experiences a gradual diminution, from the action of the sun and rain and from the heat of the earth; hence a phenomenon universally attendant on glaciers--the issue of a stream of ice-cold turbid water from the lower end. The descent of glaciers is shown by changes in the position of masses of rock at their sides and on their surface. As glaciers move they pile up moraines, consisting of accumulations of stones and gravel, along their sides and at their lower ends. These are composed of fragments of rock detached by the action of frost and other causes (See MORAINE). The fissures or crevasses by which glaciers are traversed are sometimes more than 100 feet in depth, and since they are often covered with snow, they are exceedingly dangerous to travelers. One of the most famous glaciers of the Alps is the Mer de Glace, belonging to Mont Blanc, in the valley of Chamouni, about 5700 feet above the level of the sea. However, in the chain of Monte Rosa the phenomena of glaciers are exhibited in their greatest sublimity, as also in their most interesting phases from a scientific point of view. Glaciers exist in all zones in which mountains rise above the snowline. Those of Norway are well known and also those of Iceland and Spitzbergen. Hooker and other travelers have given accounts of those of the Himalayas. Glaciers are conspicuous on the Andes, while the Southern Alps of New Zealand rival in this respect the Alpine regions of Switzerland. The glaciers of Alaska are noted for their size and grandeur. They reach their greatest development along Glacier Bay and around Mount Fairweather, where, excepting those of polar regions, the largest glaciers of the world are found. Compared with these the glaciers of the Alps are mere rivulets. Among the most noted are the Malispena, on Yakutat Bay, 1550 feet high, with an area of 600 square miles; the Valdez, in Prince William's Sound, fifteen miles long; the Muir. at the head of Glacier Bay 200 feet high with a frontage three miles long and the Pacific Glacier, off Mount Fairweather. Extensive glaciers are also found around Cook's Inlet and along the Peninsula of Alaska. All of the valleys of the northern Alaskan coast are filled with ice rivers, and the fiords of this entire region have been formed by glacial action. In numerous instances the glaciers have plowed out gorges many feet below the level of the sea. The problem of the descent of glaciers is of extraordinary interest, and various theories have been put forward to account for it. It was shown that a glacier moves very much like a river--the middle and upper parts faster than the sides and the bottom--and that glacier motion was like that of a mass of thick mortar or a quantity of pitch down an inclined trough. This theory is known as the viscous theory of glaciers, which presupposes that ice is a plastic body; and this plasticity has been satisfactorily explained by Prof. James Thomson, of Glasgow by the phenomenon of the melting and refreezing of ice. Water, he discovered, when subjected to pressure, freezes at a lower temperature than when the pressure is removed. Consequently, when ice is subjected to pressure it melts; if it is relieved of pressure the water again solidifies. Therefore if two pieces of ice are pressed together, they tend to relieve themselves by melting at their points of contact, and the water thus produced immediately solidifies on its escape. If ice is strained in any way it similarly relieves itself at the strained parts, and a similar regelation follows. This, when applied to the glaciers, gives a complete explanation of their plasticity. Pressed downward by the vast mass, the ice gradually yields. Melting and refreezing takes place at some parts; at others the gradual yielding at strained points goes on. In the latter process there is no visible melting, but there is the gradual yielding from point to point to the pressure above. If, however, at certain points the strain is intense, the ice becomes extremely brittle. The latter fact disposes of Tyndall's objection to Forbes's theory, which was based on the fact that crevasses proved the brittleness and not the viscosity of ice. See GLACIAL PERIOD; MER DE GLACE; MUIR GLACIER. Consult Russell's Glaciers of North America, and Tyndall's Glaciers of the Alps.