BY DRAINING THE SUB-SOIL. 



259 



in consequence of the inclination of the strata or layers of 

 clay and rock near the surface. The sub-soil is often thus 

 constituted, and these incline to the surface, or crop out upon 

 the sides of hills. The water-bearing strata which lies below 

 the sub-soil being brought to the surface, produce springs 

 which are a fruitful source of wet soils. 



The water in some cases rises up through the sub-soil by 

 the force of pressure from the neighboring highlands, and 

 produces a swamp. 



In case of sub-soil draining, the object is to intercept the 

 water below the surface by cutting through to the water- 

 bearing stratum, and forming a conduit for it to pass off. This 

 is the most difficult part of draining operations. 



(Firr. 17.) 



In order to show the nature of the difficulty, and the most 

 common methods of remedying it, let us suppose that Fig. 17 

 is a section of a piece of land : a the high land, d a swamp, 

 which may be produced by one or all of the water-bearing 

 strata a g h, which crop out at b c, and produce wetness 

 along the surface below. The water in A, meeting with the rock 

 f, rises up at e d. The land from 6 to c may be drained 

 by a ditch at b, conducting away the water at the point 

 where it reaches the surface. The land between c and d 

 may be drained by the ditch c. But as the water-bearing 



