246 ON THE DESTRUCTION OF ROCKS' 



water which is here the moving force. Aided by the power 

 of gravity, or urged by the violence of the winds, it 

 impels against each other and against the solid rocks, 

 those fragments which have been detached; reducing 

 them to powder, or to sand and clay, as far as its 

 power extends ; and, where that has been exhausted, 

 leaving the larger fragments at rest on the plains or 

 on the bottom of the ocean. The efforts of this 

 power are most conspicuous in mountainous countries, 

 where the agents may be seen at work in the bed of 

 every torrent; but if we would look for the effects 

 which it produces, we must search the plains, the 

 rivers, and the bottom of the sea. It is here that 

 nature accumulates the collected labour of ages in 

 one spot,, as evidences of the power of that element 

 which the geologist must never forget, Time. 



It is easy to examine, even the smallest effects of 

 friction, in the rounding of the stones found in the 

 beds of rivers, and in the sand and clay which they 

 deposit. Near the sources of the torrents, the frag- 

 ments of rocks are angular and the waters are clear, 

 except where they may invade a soil already decom- 

 posed. As we proceed along their courses, marks 

 of wear are perceived in the stones which they hurry 

 along: by degrees they become rounded, gravel and 

 sand are intermixed with them, and, as at length we 

 reach the plains, the finest particles alone are suspended 

 in the shape of clay; being deposited along its course 

 as the velocity slackens and as gravity may direct; 

 and, at length, as they outlive these actions, carried 

 into the ocean, thence never to return again in the 

 same forms. 



The marks of this force are no less visible on the 

 solid rocks ; in the deep furrows which are every 

 where to be seen in the beds of rivers, produced by 



