IMPROYEMEN^T OF SOILS. 31 



drains at close intervals ; and, on the contrary, a pervious 

 material should have deeper drains at Avider intervals. If 

 a thin bed of clay rests upon a porous substratum, the 

 drains may be cut into the latter, or through it, accord- 

 ing to its depth ; and they must then be laid at fre- 

 quent intervals. When the case occurs, as it sometimes 

 does, that a free supersoil, about three feet in depth, over- 

 lies a comparatively thin bed of clay, it is often advisable 

 to limit the depth of the drains to that of the porous 

 bed. When springs, which are fed from a higher level, 

 lie immediately below a clay substratum which exceeds 

 the practicable depth of the drains, recourse may be had 

 to tapping, by means of an auger-hole or vertical bore, 

 which will open communication to the drains, by which 

 the contents of the spring may be carried off, and the 

 liability to mischief caused by their bursting forth at a 

 lower level will be prevented. 



The drainage of deep and wet boggy land is a gradual 

 process, requiring sometimes years of patience before 

 success is attained. Frequent open ditches should, at 

 first, be cut as deep as the sides will stand, and then 

 gradually deepened as the land subsides, taking care 

 always to keep them well cleaned out. When the land 

 has become sufficiently consolidated, the usual pipe 

 drains may be put in, but they should be laid rather be- 

 yond the depth which would be thought necessary in a 

 firmer soil of the same nature. If the moss will not 

 carry the ordinary pipes, it will be advantageous to use 

 collars with them, in order to prevent their displacement. 



Marshes, and oven lakes, which occupy a bowl-shaped 

 cavity, rendering drainage by the ordinary means im- 

 practicable, have often been successfully drained by bor- 

 ing or digging through the impermeable surface layer 

 where it is not thick, and rests upon a porous substratum 

 of sufficient depth to receive the water and drain it from 

 the surface. But this method must not be tried without 



