OPERATIONS OF DRAINING, 



105 



to reach the water in its subterraneous channel before it 

 shall arrive at the surface, and carry it away in a drain. 



" By cutting a drain at A, fig. 6, the water of the 

 stratum of sand, C E, is cut off before it reaches the sur- 

 face at E, where it forms the swamp, C D. 



" In hke manner, in fig. 7, by forming a drain at C, 

 or F, the water is cut off in its channel A B, and thus, 

 in reheving the pressure from a higher source, by giving 

 egress to the water through the drain, the cause of the 

 wetness from E to D is removed. 



" In looking at the slo- 

 ping surface of any tract of 

 ground, as a field, in which 

 there is an oozing or burst- 

 ing out of water, we shall 

 generally distinguish the line 

 where the wetness appears 

 upon the surface, extending 

 over a considerable space, 

 X X X X x^ fi^. 8^ the effects 

 appearing in the wetness of 

 the ground further down the 

 slope, as y y y- The line 

 where the wetness begins, 

 which is generally rendered 

 perceptible by the change 

 of color of the soil, the ten- 

 dency to produce subaquatic 

 plants, and other indications 

 of wetness, marks, for the 

 most part, nearly the course 

 which the line of the drain 

 should follow. By cutting 

 a drain nearly in this line, 

 as from G to A, sufficiently 

 deep to reach the stratum in 

 which the water percolates, 

 we shall intercept it before it reaches the surface, and by 

 carrying it away in some convenient outlet, A B, remove 

 the cause of wetness. 



