80 AGRICULTURE 



sometimes or old bricks or stones. Although these are 

 buried several feet in the ground, water flows down to 

 them, thus deepening and airing the soil. They usually 



FIG. 52. DRAIN TILES IN POSITION UNDER- 

 GROUND 



CG. 53. END VIEW OF 

 DRAIN TILE BEFORE THE 

 DITCH is FILLED 



drain the soil more completely and to greater depth 

 than do ordinary open ditches. 



Open ditches. According to their use, the principal 

 kinds of open ditches are : 



1. Canals, or very large ditches. 



2. Deep drainage ditches. 



3. Hillside ditches (usually shallow ditches). 



The water in open ditches often carries much mud and 

 other fine material. When the current is rapid, this soil 

 material is carried onward by the water, and is not depos- 

 ited. But if any part of the ditch is less steep than the 

 portion above it, the water must necessarily travel more 

 slowly. A sand-bar generally forms where the current is 

 thus checked, for the slower current is unable to carry its 



