IMPROYEMEKT OF SOILS. 35 



outfall. The last pipe of the main should pass through 

 brickwork whose foundation is laid below the level of 

 the bottom of the ditch, and it should be protected by a 

 flap or- gird. And the exit-water should fall from this 

 opening on to a slab of stone laid on the bottom of the 

 ditch, so as to hinder any risk of undermining the brick- 

 work by its continual fall. 



The cost per acre of land-draining is more generally 

 covered by the consequent increased value of the land, 

 than that of any other agricultural improvement. What- 

 ever the interval or depth, the expense depends on the 

 character of the soil or subsoil, the local rate of wages, 

 the cost of the tiles, and the distance of the kiln. 



In all cases it will be understood that the end desired 

 is the nearest possible approach to the natural examples 

 of the best soil resting on pervious subsoils, where the 

 rainfall finds a gradual passage through the soil and sub- 

 soil, sinking always where it falls, carrying the generally 

 warmer temperature of the air into the land — carrying 

 also many an element of plant food, which the air con- 

 tains, directly to the roots of plants — carrying, too, the 

 air itself, the great oxidizer, amidst the matters organic 

 and inorganic which require its influence for their con- 

 yersion into available plant food — proving, by its action 

 as a solvent, and its passage over the immense inner 

 superficies of the soil, an active caterer for the stationary 

 roots. At the same time it is hindered from doing the 

 mischief which on undrained land the rainfall cannot fail 

 of doing. The manure particles of the soil, if they do to 

 some extent escape through drainage, are at any rate not 

 washed wholesale from the surface into the furroAvs and 

 ditches, which in the case of undrained land receive 

 them without the subsoil having had a chance of retain- 

 ing them. 



Irrigation* — This, which at first seems the exact con- 



