ICE-FLOODS. 57 



witnessed the breaking up of a river in the spring 

 after a severe winter, when its whole surface has 

 been covered by ice several feet thick, has but a 

 faint idea of the prodigious force exerted at such a 

 time. The ice high up the stream is usually first 

 broken in pieces by the swollen waters. Large 

 masses are thus thrown up edgewise, and forced 

 underneath the unbroken sheet, and the whole bed 

 of the river is blocked up — perhaps, too, where the 

 banks are high and rocky. The water accumulates 

 behind the obstruction until the resistance is over- 

 come, and the huge mass of water and ice urges on 

 its way, crushing and jamming together that which 

 it meets, and thus gaining new strength at every 

 step. Often for miles the stream, prodigiously 

 swollen, is literally crammed with ice, so that the 

 water disappears, and a slowly-moving column of 

 ice is all that is seen. This presses with such force 

 upon the bottom and sides of the river-bed as to 

 cause the earth to tremble, with a sound like heavy 

 thunder, for a distance of miles. Sometimes the 

 body of ice becomes so large, and the friction so 

 great, that the waters are unable to keep it in mo- 

 tion, and it stops, while the river is turned out of its 

 channel, and is compelled to flow in a new bed for 

 weeks and even months." 



This cause has a wonderful eff'ect in excavating 

 the beds of rivers. It sometimes tears up great 

 rocks, and pushes them for a considerable distance. 



