SOLIDS, LIQUIDS, AND GA8E8. 373 



is thawed and evaporated, it must either go on growing 

 upward until it reaches the highest atmospheric region 

 from which it falls, or is formed, or it must descend some- 

 how. 



If ice can be squirted through a syringe by mere hand- 

 pressure, we are justified in expecting that it would be 

 forced down a hill slope, or through a gully, or across a 

 plain, by the pressure of its own weight when the accumu- 

 lation is great. Such is the case, and thus are glaciers 

 formed. 



They are, strictly speaking, rivers or torrents of ice; they 

 flow as liquid water does, and down the same channels as 

 would carry the liquid surface drainage of the hills, were 

 rain to take the place of snow. Like rivers, they flow with 

 varying speed, according to the slope; like rivers, their cur- 

 rent is more rapid in the middle than the sides; like rivers, 

 they exert their greatest tearing force when squeezed 

 narrow thorugh gullies; and, like rivers, they spread out into 

 lakes when they come upon an open basin-like valley, with 

 narrow outlet. 



The Justedalsbrae of Norway is a great ice-lake of this 

 character, covering a surface of about 500 square miles, 

 and pouring down its ice-torrents on every side, wherever 

 there is a notch or valley descending from the table-land it 

 covers. The [rate of flow of such downponring glaciers 

 varies from two or three inches to as many feet per day, 

 and they present magnificent examples of the actual flu- 

 idity or viscosity of an apparently solid mass. This vis- 

 cosity has been disputed, and attempts have been made to 

 otherwise explain the motion of glaciers; but while it is 

 possible that it may be assisted by varying expansion and 

 contraction, the downflow due to viscosity is now recog- 

 nized as unquestionably the main factor of glacier motion. 



Cascades of ice may be sometimes seen. In the course 

 of my first visit to Norway, I wandered alone over a very 

 desolate mountain region towards the head of the Jnstedal, 

 and unexpectedly came upon a gloomy lake, the Stygge- 

 vand, which lies at the foot of a precipice-boundary of the 

 great ice-field above named. Here, the ice having no 

 sloping valley-trough by which to descend, poured over the 



