ON THE ACTION OF RIVERS. 447 



rocks in, <the neighbourhood of the lofty mountains in 

 which they took their rise, often gain in volume what 

 they have lost in velocity ; but the power dependent up- 

 on size rarely compensates that which they owed to ra- 

 pidity ; and although these large rivers still retain a 

 transporting power, sufficient to carry along with them 

 the obstacles which oppose themselves to their progress, 

 they are far from presenting results of action so striking 

 as those of torrents. They stir up, when flooded, or 

 when they change place, the earth and mobile sand which 

 cover their bottom, especially towards their edges, and 

 transport them to some distance ; but they scarcely move 

 pebbles larger than an egg, which occur in their bed, 

 and which have been brought there in other times, and 

 under other circumstances. Ori thus transporting the 

 comminuted and mobile mineral matters, they deposite 

 them again in places where their current is relaxed by 

 some cause, and thus raise the bottom of their bed in 

 these places ; they seek a new passage in the midst of 

 the barriers which they have themselves constructed. 

 The principal current is then borne, sometimes against 

 one bank, and sometimes against the other ; and when it 

 comes to beat upon the foot of a steep part, composed 

 of moveable soil, as the banks commonly are, in such 

 cases, they really erode it, and make it fall into the river ; 

 and transport to another part of its course, the earth re- 

 sulting from the destruction of the bank, and give rise 

 to new obstacles. Hence the new deposites, which bor- 

 der rivers in all -points where their current is slackened, 

 and principally toward their mouth. It is sufficient for 

 our present purpose to have referred to facts remarkable 

 for their number, for the importance which they have had 



