THE WORK OF SNOW AND ICE. 259 



neve, then with snow, and finally merges into the snow-field without 

 ha^dng ceased to be a glacier. The term glacier is, however, commonly 

 used to mean merely the more sohd portion outside (below) the neve. 



Movement. — The fact of glacier movement is established in various 

 ways, the most ob\ious being by the advance of its lower end. Such 

 advance is too slow to be seen from day to day, and is only detected 

 when the lower end of the glacier overrides or overturns objects in front 

 of it, or moves out over ground previously unoccupied. But even 

 when the end of a glacier is not advancing, the movement of the ice 

 may be estabHshed by means of stakes or other marks set on the sur- 

 face. If the positions of these marks relative to fixed points on the 

 sides of the valley be determined, they are found after a time to have 

 moved down the x'alley. Rows of stakes or fines of stones set across 

 a glacier in the upper, middle and lower portions have revealed many 

 facts concerning the movement of the ice. 



Generally speaking, the middle of a valley glacier moves more 

 rapidly than its sides (Fig. 236), but in some cases, especially in large 

 glaciers, there are found to be two or more main fines of movement, 

 with belts of lesser movement between. The top of a glacier moves, 

 on the whole, more rapidly than the bottom, though the observations 

 made do not show that the rate of movement diminishes regularly 

 downward, and it probably does not so dinfimsh in many cases. In 

 Switzerland, where the glaciers have been studied more carefully than 

 elsewhere, the determined rates of movement range from one or two 

 inches to four feet or more per day. Some of the larger glaciers in 

 other regions move more rapidly, but it does not follow that large 

 glaciers alwa^^s move faster than small ones. The Muir glacier of 

 Alaska has been found to move seven feet or more per day,^ and some of 

 the glaciers of Greenland have been found to move, in the summer time, 

 50, 60, or even more feet per day. A single estimate as high as 100 

 feet per day has been made; but these high rates have been observed 

 only where the ice of a large inland area crowds dovm into a compara- 

 tively narrow fjord, and debouches into the sea, and then only in the 

 summer. In the case of the glacier with the highest recorded rate 

 of summer moA^ment, 100 feet per day, the advance was only 34 feet 

 at about the same place in April. 



^Reid. Natl. Geog. Mag., Vol. IV, p. 44. 



