SOILS AND THEIR COMPOSITION 165 



substance. The grit that worms take in acts like mill- 

 stones and grinds the stomach contents up in the same 

 way as is done in the gizzard of a bird. In fact this 

 grinding up of mineral substances, called trituration, 

 is one of the most important operations in the forming 

 of new rocks, and is very greatly helped by the common 

 earthworm, whose activity is anything but negligible 

 geologically, apart from what is to us as growers, of more 

 immediate benefit in the way of soil formation. 



It will thus be seen that were it not for the common 

 earthworm there would have been very Uttle soil for 

 plants to grow in, and I would also observe that the 

 hills and dales which look so soUd and immoveable to 

 us, are by no means permanent features, as they change 

 from year to year by these seeming small modifications 

 wrought by apparently insignificant creatures like the 

 garden worm. 



Having our soil thus prepared for us as a bountiful 

 gift from the hand of nature, we must endeavour to carry 

 on as much as we can a perfectly natural process of 

 growth. Wherever we depart from this we are bound 

 to discover, as years go on, that too heavy cropping means 

 soil exhaustion at a rate greater than is made up for 

 by the ordinary restorative action. The making good 

 of such a state of affairs is called manuring, and I propose 

 to conclude our present programme in the chapter that 

 follows with a few notes on that subject. 



