868 



THE COMPLETE GRAZIER. 



Thus let a b (fig. 372) be the main drain ; all the drains c c, running 

 down the slope tending from d e to a b, drain directly into the main 

 drain a b. But, on the other side of the main drain a b, the field does 

 not slope towards the main, but slopes in two different directions. 

 Thus the vacant line / g represents the ridge or highest part, the slope 

 on one side of this being from/# to h h, and on the other from fg to 

 i i. The one side or slope of the hill k k is therefore drained by drains 

 kk, leading into the " sub-main " h h, which again communicates with 

 the main drain a b the other side or slope I I being drained by the 

 drains I I, leading into the " sub-main " i i, and that finally into the 

 " main " a b. 



A common kind of plan is shown in fig. 373. It represents an 

 undulating surface in which the " mains " are placed at the lowest 



Fig. 373. Plan of Drainage. 



levels, and the minor drains run into them in the direction of the 

 inclinations of the ground. 



The Depth of the Drains. This is decided by a variety of circum- 

 stances. It is usual in many cases to dig a series of holes called " test 

 holes " in the field ; or, if preferred, deep cuttings may be made ; these 

 should be dug in the line of intended drains, in order to become 

 ultimately available as drains. Mr. Bailey Denton, one of our leading 

 modern authorities on drainage, states, with reference to test holes, 

 that they are only trustworthy when applied to light or free soils, and 

 that they afford no index to what is required in the drainage of heav^y 

 clay soils. 



The great object to be kept in view, in deciding the depth of drains, 

 is to allow that depth which draws the greatest amount of water from 

 the widest extent of land on each side of the drain. The greater the 

 number of cubic yards of soil drained, the more perfect is the drain ; 



