G1VORS 



Givors. Town of France, in the 

 dept. of Rhone. It lies about 14 m. 

 S. of Lyons, with a station on the 

 Paris-Lyons-Mediterranean line, on 

 the right bank of the Rhone at the 

 confluence with the river Gier. The 

 town's chief industries are metal 

 working and glass-bottle manufac- 

 tures, and there is considerable 

 trade in silk and coal. Pop. 12,784. 



Gizeh OR GHIZEH. Prov. of 

 Lower Egypt. It contains the 

 districts of Ayat, Es Saff, Embaba, 

 and Gizeh. Area, 398 sq. m. Pop. 

 524,352. 



Gizeh. Town of Egypt. It 

 stands on the left bank of the Nile, 

 opposite the island of Roda, just 

 above Cairo. Here is the palace of 

 Gizeh, erected by the khedive 

 Ismail. In the neighbourhood are 

 the Pyramids. Pop. 18,714. See 

 Egyptian Art, colour plate. 



Gizzard (Lat. gigeria, poultry 

 entrails). Term used in compara- 

 tive anatomy for that portion of 

 the alimentary canal which is 

 specially designed for grinding food. 

 Hence it is usually found in such 

 animals as swallow food whole with- 

 out mastication. It is well seen 

 in the domestic fowl, where the 

 action of its muscular walls is aided 

 by bits of gravel swallowed by 

 the bird. Many crustaceans and 

 insects possess gizzards. 



Glace Bay. Town and port of 

 Cape Breton Island, Nova Scotia, 

 Canada. A station on the Sydney 

 and Louisburg Rly., it is 14 m. 

 from Sydney, with which it is also 

 connected by electric rly. Around 

 it are coal mines, and its industries 

 include machine and rly. shops and 

 fishing. It has a wireless station, 

 and is a market for the produce of 

 the neighbourhood. Pop. 16,562. 



Glacial Period. Name given to 

 one of the great stages of develop- 

 ment in the earth's history. It is 

 the earlier of the two subdivisions 

 of quaternary time. See Ice Age. 



Glacier (Fr.). Moving mass of 

 ice. The edge of the permanent 

 snow, the snow-line, varies in ele- 

 vation from sea level in Antarctica 

 to 2,500 ft. in Alaska, 8,500 ft. on 

 the Alps, and 16,000 ft. on the S. 

 side of the Himalayas. 



As the snow above the perman- 

 ent snow-line accumulates, the 

 lower portions, adjacent to the 

 rock, slowly change into ice ; and 

 when the mass of ice and snow 

 becomes sufficiently thick it begins 

 to make new adjustments to the 

 land contours, and to move down 

 the slopes. When the moving 

 mass follows a definite path down 

 a mountain valley, it is a glacier. 



The physical changes which occur 

 when ice moves under pressure 

 have not been precisely determined. 

 Owing to irregularities in the rock 



3541 



GLACIER 





Glacier. The Mer cle Glace, near Chamonix. 4i miles in length; 

 glacier which moves down the north side of Mont Blanc 



the 



contour, deep cracks or crevasses 

 occur in the upper glacier layers ; 

 they are sometimes hidden by a 

 thin snow bridge, and are a source 

 of ever-present danger. In its 

 passage downwards, a glacier ac- 

 cumulates large quantities of 

 rocks. Some of these sink into the 

 mass of ice ; others are moved to 

 the margins of the glacier because 

 the middle moves more rapidly 

 than the sides. The debris of the 

 edges is known as lateral moraines. 

 The snout of a glacier occurs 

 where the temperature melts the 

 ice as fast as it is brought down ; 

 in many cases the snout advances 

 or retreats during different periods. 

 From the snout a turbid, milky- 

 looking torrent rushes down the 

 valley, and when the snout retreats 

 it leaves rock debris, which forms 

 a terminal moraine. 



Types of Glacier 



Glaciers have been classified into 

 four types : (1) valley glaciers ; (2) 

 piedmont glaciers ; (3) ice caps ; 

 (4) continental glaciers. Valley 

 glaciers occur in the Alps, where 

 the Aletsch is 10 m. long and 1 m. 

 wide ; in the Caucasus, Andes, 

 Himalayas, and among the coast 

 nits, of Alaska, where the Muir 

 glacier is 35 m. long and from 6 to 

 10m. wide. Alpine glaciers termin- 

 ate on land, but the Alaskan 

 glaciers reach the sea, and portions 

 break off and float away as ice- 

 bergs. The rate of movement of 

 some valley glaciers has been 

 measured ; the Mer de Glace in 

 France moved during the warm 

 season from 1 ft. to 1 ft. a day 

 along the margin, and about 2 ft. 

 daily in the middle ; the Muir 

 glacier moved 7 ft. daily in the 

 middle. The rate varies with the 

 season, and from year to year. 



Piedmont glaciers occur when a 

 valley glacier pushes out on to a 

 nearly level area at the base of the 

 mountains. The Malaspina pied- 

 mont glacier, fed by numerous 

 valley glaciers, is 70 m. by 25 m. 

 Formation of Icebergs 



Ice caps occur in Iceland; the 

 largest is at Vatna Jokull. In this 

 case the ice moves very little, 

 owing to the level character of the 

 rock contours. Extensive ice caps 

 are called continental glaciers, or 

 ice sheets. Greenland and Ant- 

 arctica are both covered with ice 

 formations of this type. The great 

 depth of the ice sheet causes out- 

 ward movement, and in Antarc- 

 tica the great ice barrier, an ice 

 cliff margin to the Ross Sea, is 500 

 m. in length, and rises sheer from 

 the water to heights from 30 ft. to 

 nearly 300 ft. The Greenland con- 

 tinental glacier is steadily pushing 

 seawards, the tongues of ice pro- 

 ject into the water, in some cases 

 with a front 60 m. in width. These 

 tongues move at rates between 5 

 and 75 ft. per day, and are con- 

 stantly losing great blocks, which 

 feed the never-ending stream of 

 bergs in the N. Atlantic. 



The various signs left by retreat- 

 ing glaciers terminal moraines, 

 layers of glacier silt (till or 

 boulder clay), isolated rock frag- 

 ments, rounded rocks (roches 

 moutonnees), striations upon rock 

 faces, etc. are so common in 

 Britain N. of the Thames, and in 

 Europe, N. of Bohemia, that it is 

 concluded that most of Europe has 

 been covered at least once by a 

 continental glacier of Antarctic 

 magnitude. See Finsteraarhorn ; 

 Geology; Ice Age; consult also 

 Glaciers of the Alps, J. Tyndall, 

 1896; Ice- Work, Present and Past, 

 T. G. Bonney, 1896. 



