100 



OPERATIONS OF DRAINING. 



face, they will let in surface-water, with the earthy mat- 

 ters which it contains, and which will ultimately fill the 

 interstices and choke up the drain. The stones should 

 be broken to a size not to exceed four inches, the ex- 

 pense of doing which will not exceed 25 to 30 cents the 

 cubic yard. If a stone conduit is laid, or tiles are em- 

 ployed, the first covering of them should be broken stone, 

 or porous materials, to a convenient height, in order that 

 the water settling from above, may find free access to the 

 drain. Conduits of stone are seldom necessary in furrow- 

 draining — it being sufiicient to break and throw in stone 

 from 12 to 24 inches in depth. 



Conduits to under-drains are made by building a little 

 wall, roughly, with stone or brick, on each side at the 

 bottom, about 6 inches in height, so as to leave a passage 

 for the water six inches in width and six inches high. 

 These side-walls are covered with flat stones, as close as 

 can be conveniently placed, and straw or htter thrown 

 over to defend the conduit from earth and other substan- 

 ces which might get into it before the ground has become 

 compact and firm. When this is done, broken stones 

 may be thrown in promiscuously, if they are at hand, to 

 the height of 6 to 24 inches, according to the supply and 

 the depth of the drain ; and the earth then filled in and 

 rounded upon the surface. A drain thus formed will ap- 

 pear on a transverse section as in fig. 1, and after the 

 subsidence of the earth as in fig. 2. Where the earth is 

 Fig. 1. Fig. 2. 



