ON THE DESTRUCTION OF HOCKS. 247 



the incessant friction of the heavy bodies carried along 

 their surfaces. These furrows, it is well known, are 

 found in places where rivers no longer flow, and they 

 have been supposed the marks of antient deluges. In 

 many of the instances that have been adduced, they 

 are clearly the effects of rivers which have changed 

 their places ; but as there is much that depends on 

 this question, unconnected with the present inquiry, 

 it needs not be agitated at present. 



As the accumulated products of friction are best exa- 

 mined in the plains and on the sea shores, so its effects 

 on the solid rocks may most advantageously be wit- 

 nessed in the deep sections which the torrents pro- 

 duce in the mountains. That these are really the 

 effects of friction, is proved by the accurate corre- 

 spondence of the rocks on the opposite sides. But no 

 where is it more clearly evinced than in the falls of 

 rivers, where these forces act with increased energy ; 

 the traces of cascades being frequently found far re- 

 mote from the present places of the falls, and pre- 

 serving the most impressive records of all that has 

 been destroyed. 



But it is not only in rivers that the power of water is 

 exerted in causing the hard materials of the earth to 

 contribute to each other's destruction. The fragments 

 which rains and frosts have separated from the cliffs 

 of the sea shore, rolled without ceasing by the efforts 

 of the waves and the tides, are gradually reduced to 

 powder; forming beds of sand and mud, and contri- 

 buting, during their own destruction, to that of the 

 solid rocks against which they are incessantly impelled. 

 But the great destruction of the sea cliffs, that of 

 which the traces are so strongly recorded in the out- 

 lines of all rocky coasts, is produced by causes of a far 



