The trituration of small particles of stone in the gizzards of worms is of more importance 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 110 of an inch in diameter would be worn ten times as much as one 1100 of an inch in diameter, and at least a hundred times as much as one 11000 of an inch in diameter. Perhaps, then, we may conclude that a grain 110 an inch in diameter would be worn as much or more in drifting a mile as a grain 11000 of an inch in being drifted 100 miles. On the same principle a pebble one inch in diameter would be worn relatively more by being drifted only a few
