106 THE PRINCIPLES OF 



are not very common. Mr. Elkington, living as he did in 

 Warwickshire, where the lower oolites, the lias clay, and the 

 new red sandstone all verge upon each other, they furnished 

 the peculiar alternation of retentive and porous strata which 

 are necessary; but it is scarcely likely that we shall find 

 many localities where land can be drained according to this 

 dexterous method. Still, clay soils which are underlaid by a 

 gravel bed may in some measure be treated on Elkington's 

 principle. For example, we may take the case of a clay 

 soil where some six feet beneath the surface occurs a porous 

 gravel bed. To drain such ground as that three feet deep 

 would be a mistake. It would be much better to take a leaf 

 out of Elkington's book, and place the drains seven feet deep, 

 get them down well into the gravel bed, and then we should 

 have a sort of connective medium between the drains which 

 would enable us to place them at great distances apart. 

 Instead of placing our drains in the compact clay three feet 

 deep and twenty-one feet apart, we should sink them seven 

 feet in depth, and with the aid of the gravelly bed which lies 

 under the clay, increase our intervals to forty or fifty yards 

 apart ! This is well known to practical drainers, who some- 

 times go as deep as ten or eleven feet in order to tap a porous 

 substratum. 



Before draining a large tract a thorough examination of 

 the soil section should be made. Sometimes drains are con- 

 structed partly after Elkington's system and partly after 

 Smith's system. Springs must be tapped, and hidden shifting 

 sands must be reached by a separate system of drains placed 

 below the contemplated depth of the ordinary regular drains. 

 Then having relieved the land from its springs we proceed 

 with our regular system of drains eighteen, twenty, or 

 twenty-five feet apart, the traversing drains being laid a few 

 inches deeper. Again, sometimes on hill- sides it is necessary 

 to cutoff the soakage water from higher levels by a drain cut 



