OPERATIONS OF DRAINING. 103 



siderable, it should be open, but covered in all other 

 cases. 



There is another mode, which is sometimes success- 

 fully practised, of getting rid of the water which reposes 

 upon the subsoil, when the stratum of the subsoil is thin, 

 and lies upon a porous gravel or sand ; which is, by bo- 

 ring or digging through the subsoil, so as to let the water 

 pass into the porous stratum below. In this case the 

 holes or pits are generally filled with stones, and the drains 

 conducted to them. 



3. Subsoil draining, or the drainage of waters that 

 rise through the subsoil, or pass off at its outcroppings, 

 as upon the declivities of hills, &c. In discussing this 

 section, we shall principally quote from Professor Low's 

 Elements of Practical Agriculture. 



" It is the intercepting of water below the surface that 

 constitutes the most difficult part of draining, and which 

 requires the application of principles which it is not ne- 

 cessary to apply in the case of surface-draining. 



" If we shall penetrate a little way into the looser por- 

 tion of earth, we shall generally find a minute stratification, 

 consisting of gravel, sand, or clay, of different degrees of 

 density. These strata are frequently horizontal, frequent- 

 ly they follow nearly the inclination of the surface, and 

 frequently they are broken and irregular. Sometimes the 

 stratum is very thin, and a few inches in thickness, and 

 sometimes it is several feet thick ; and sometimes the 

 traces of stratification disappear, and we find only, to a 

 great depth, a large mass of clay or other homogeneous 

 substance. 



"When these substances are of a clayey nature, water 

 finds its way through them with difficulty ; when they are 

 of a looser texture, water percolates through them freely. 

 These, accordingly, form the natural conduits or channels 

 for the w^ater which is below the surface, when finding its 

 way from a higher to a lower level. 



" When any bed or stratum of this kind, in which 



water is percolating, crops out to the surface, the wa- 



*ter which it contains will flow out and form a burst 



or spring, oozing over and saturating the ground, as in 



