THEORY OF THE EARTH. 47 



When the snow melts, or when a storm takes 

 place, these mountain torrents become suddenly 

 swelled, and rush down the declivities with a vio- 

 lence and rapidity proportioned to their steepness : 

 They dash against the feet of these taluses of fallen 

 fragments which form the sides of all the elevated 

 valleys, carrying along with them the rounded frag- 

 ments of which they are composed, which become 

 smoothed and still farther polished by rubbing on 

 each other. But, in proportion as the swollen 

 torrents reach the more level valleys, and the force 

 of their current is diminished, or when they arrive 

 at more expanded basins which allow their waters 

 to spread out, they then throw out on their banks 

 the largest of these stones which they had rolled 

 down : The smaller fragments are deposited still 

 lower ; and, in general, nothing reaches the great 

 canal of the river except the minutest fragments, or 

 the impalpable particles, which afterwards sub- 

 side to form mud. It often happens also, before 

 these streams unite to form great rivers, that they 

 have to pass through large and deep lakes, where 

 they deposit the mud brought down from the 

 mountains, and whence their waters flow out quite 

 limpid. 



The rivers in lower levels, and all the streams 

 which take their rise in the lower mountains or hills, 

 produce effects on the grounds through which they 

 flow, more or less analogous to those of the tor- 

 rents from the higher mountains. When swelled 



