Chap. V. AND DEN UDATION. 257 



The trituration of small particles of stone 

 in the gizzards of worms is of more import- 

 ance under a geological point of view than 

 may at first appear to be the case ; for Mr. 

 Sorby has clearly shown that the ordinary 

 means of disintegration, namely running 

 water and the waves of the sea, act with 

 less and less power on fragments of rock the 

 smaller they are. " Hence," as he remarks, 

 " even making no allowance for the extra 

 " buoying up of very minute particles by a 

 ''current of water, depending on surface 

 " cohesion, the effects of wearing on the form 

 " of the grains must vary directly as their 

 " diameter or thereabouts. If so, a grain ^ 

 "of an inch in diameter would be worn ten 

 " times as much as one ^ of an inch in 

 " diameter, and at least a hundred times as 

 "much as one 10 1 00 of an inch in diameter. 

 " Perhaps, then, we may conclude that a 

 " grain y 1 ^ of an inch in diameter would be 

 u worn as much or more in drifting a mile as 

 * a grain -j-^- of an inch in being drifted 

 " 100 miles. On the same principle a pebble 

 "one inch in diameter would be worn re- 

 14 latively more by being drifted only a few 



