124 ON THE BEST METHOD OF 



in thickness; beneath it lies the marly clay upon which we 

 g-enerally lay the tiles. But it sometimes happens that on 

 the hig-her parts of the field the clay referred to cannot be 

 reached, on account of the increased thickness of the sand. 

 Still when this is the case, the sand beneath the stratum of 

 water, on account of its elevation, is of a firmer and drier 

 kind, upon which we can with confidence place the tiles, 

 never having- found them to fail when a rapid descent was 

 avoided. To reach the clay in every place is not practicable. 

 The average depth of the drains is about 3^ feet. 



The manner in which the work is done is as follows : — 

 The first object is to ascertain the depth at which the bottom 

 water lodges. If deep, and the earth very porous, the 

 drains are set out much farther apart than when it lies near 

 the surface. Thus they are varied in their distance from 

 each other in proportion as the water lies deep or otherwise ; 

 that is to say, when we can cut to a depth of 4 feet in that 

 which is entirely porous, the drains are set 15 yards apart, 

 and when we find the water to lie as deep as 6 feet, their re- 

 lative distance is 20 yards. But when the clay lies near 

 the surface, being only about 12 inches beneath it in some 

 instances, they are set out only 8 yards apart. 



Having ascertained the proper depth and relative distances 

 of the drains, the outlet is next attended to, a point which is 

 frequently too slightly regarded, and consequently often 

 proves injurious, and sometimes entirely ruinous to the whole 

 work. When this is accomplished, the drains are set out as 

 above. The land, which is ver}^ undidating, is cut to a cer- 

 tain level depth throughout, so as to give a gradual and 

 proper descent towards the outlet, and so deep as to only 

 require two draws or spits to be taken out afterwards. The 

 earth at the top being thus removed, the level is then used 

 (as, from the porousness of the land, no water by which the 

 descent might be taken runs so near the surface), and the 

 greatest care is taken at this stage of the work to have all 

 thoroughly true, and the descent given that is required, as 

 the finishing depth and the fall are ruled by the top level- 

 ling, before the two spits referred to are taken out. To cut 

 the drains deeper before using the level, would be to render 

 the use of it almost impracticable. 



All is now ready for completing the work, tiles and bot- 

 toms being laid by the side of the drain, and three men 

 engaged in the work; two of the most experienced to cut 

 the drain to its proper depth, the one following- the other in 



