Ice Floods. 



139 



will give a descent from the latter place to the ocean of only a foot 

 per mile, and considerably less if we subtract the height of Enfield 

 Falls. South Hadley Falls make the principal difference between 

 Springfield and Northampton. Indeed, the medium descent of this 

 river from the foot of Turner's Falls in Gill, is probably less than a 

 foot per mile. This is too small to enable the waters to produce 

 scarcely a perceptible effect in lowering their bed, for centuries, nay, 

 not enough to prevent their filling it up. So that probably the process 

 of excavation in the bed of that river, has nearly ceased. 



Ice Floods. 



There is, however, one agent of excavation, that still operates to 

 some extent,. even in the Connecticut ; and that is, ice floods. Still 

 more powerful is their effect upon smaller and more rapid rivers. 

 Whoever has not 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 stream is blocked up ; perhaps too, where the banks are high 

 and rocky. The water accumulates behind the obstruction until the 

 resistance is overcome ; and the huge mass of water and ice urges on 

 its way, crushing and jamming together the ice 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 against the bottom and sides of 

 the stream, as to cause the earth to tremble, like heavy thunder, to 

 the 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. 



It is impossible that such floods should not operate powerfully to 

 modify the surface in alluvial regions, and to excavate the beds of 

 rivers. I am confident that no other agent in the mountain torrents 

 of this state is so energetic. One has only to examine the banks and 

 bed of a river after the ice has disappeared, as I have often done in 

 Deerfield, to be convinced of this. But I apprehend that the maxi- 

 mum effect is seen in those rocky ravines, through which such rivers 



