ice. 675 



back up the shore. Large accumulations of stray stones far above 

 the ordinary level of the lake are in some places thus made. 



Ice over a pond, when thick, by its expansion often pushes with 

 great force against the shores, moving what is movable on it, or, if 

 it be confined by a narrow bank, will sometimes push the bank out 

 of place. 



3. Glaciers. 



I. General Features, Formation, and Movement of Glaciers. 



1. Nature of Glaciers. — Ordinary glaciers are accumulations of ice, 

 descending by gravity along valleys from snow-covered elevations. 

 They are ice-streams, 200 to 5,000 feet deep or more, fed by the 

 snows and frozen mist of regions above the limits of perpetual frost. 

 They stretch on 4,000 to 7,500 feet below the snow-line (limit of per- 

 petual snow), because they are so thick masses of ice that the heat 

 of the summer season is not sufficient to melt them. Some of them 

 reach down between green hills and blooming banks, into open culti- 

 vated valleys. The extremities of the glaciers of the Grindelwald 

 and Chamouni valleys lie within a few hundred feet of the gardens 

 and houses of the inhabitants. Each glacier is the source of a stream, 

 made from the melting ice. The stream begins high in the mountains, 

 from the waters that descend through the crevasses to the ground 

 beneath, and often makes a tunnel in the ice above its course ; finally, 

 it gushes forth from its crystal recesses, a full torrent, and hurries 

 along over its stony bed down the valley. 



2. Glacier Regions — The best known of glacier regions is that of 

 the Alps. West of the head-waters of the Rhone, the chain is 

 divided into two nearly parallel ranges, a southern and a northern. 

 The latter includes, besides minor areas, two large glacier districts, — 

 the Mt. Blanc, and the Mt. Rosa or Zermatt district ; and the former, 

 one of equal extent, though its peaks are less elevated, — that of the 

 Bernese Oberland. There is another district of glaciers at the head- 

 waters of the Rhone, and others farther eastward. 



Glaciers occur also in the Pyrenees, the mountains of Norway,. 

 Spitzbergen, Iceland, the Caucasus, the Himalayas, the southern ex- 

 tremity of the Andes, in Greenland, and on Antarctic lands. One 

 of the Spitzbergen glaciers stretches eleven miles along the coast, and 

 projects in icy cliffs 100 to 400 feet high. The great Humboldt 

 ■glacier of Greenland, north of 79° 20', has a breadth at foot, where it 

 enters the sea, of forty-five miles ; and this is but one among many 

 about that icy land. Some American glaciers are alluded to on page 

 536. 



3. Many Glaciers from one Glacier District. — The following map 



