On Draining. 



45 



able to pass through it ; or to carry them for a few yards at a still 

 greater depth to reach an ascertained source of water ; while at 

 another time, the occurrence of the impenetrable shale above 

 mentioned bars all farther downward progress, and proclaims it 

 useless, even within 3 feet of the surface. Such is the general 

 character of the ground in which the above-mentioned trials of 

 various draining measures have been made; and where, effectually 

 as we may have withdrawn the water from beneath the yellow 

 clay," our success in drying the soil above it has certainly not 

 been uniform. 



Now, if the evidence which we have had of similar operations 

 in other quarters can be trusted, there is nothing in these cir- 

 cumstances to account satisfactorily for the failure. Clays as 

 close and deep are positively asserted to have yielded all that 

 could be desired to simple four-feet drains. In Northampton- 

 shire, in Kent, in Sussex, in Oxfordshire, in Essex, and elsewhere, 

 we are told of land of the stiffest texture — of clay almost uniform 

 from the surface to a depth beyond that to which such work can 

 be carried— undeniably dried by such means. Why, then, should 

 we meet with so much difficulty where it only forms part of a 

 more manageable series, and is not unfrequently itself of a less 

 apparently stubborn nature ? 



It strikes me forcibly that the true solution of this question 

 probably lies in an agency of which too little account has hitherto 

 been taken by our otherwise able leaders and instructors in the 

 science. Their attention has been exercised perseveringly upon 

 diversities of soil : must we not bestow more of it upon those of 

 climate ? Its differences within these islands is confessedly great ; 

 let us inquire how they are likely to affect our results. 



In order to secure the full effect of thorough drainage in clays, 

 it is necessary that there should be not only well-laid conduits for 

 the water which reaches them, but also subsidiary passages 

 opened through the substance of the close subsoil, by means of 

 atmospheric heat, and the contraction which ensues from it. The 

 cracks and fissures which result from this action are reckoned 

 upon as a certain and essential part of the process. A single 

 passage from the pen of one of the ablest masters of the science 

 will be sufficient to establish this point, though there is no lack of 

 others. Mr. Parkes says, in the valuable and w^ell -known essay 

 in the fifth volume of the Journal (p. 145), that — 



" A natural agricultural bed of porous soil resembles an artificial filter; 

 ^ and it is unquestionable that the greater the depth of matter composing 

 such filter the slower is the passage of water through it. In stiff" loams and 

 clays, however, but more particularly as regards the latter earth, the re- 

 semblance ceases, as these soils can permit free ingress and egress to rain- 

 water only after the establishment of that thorough network of cracks and 

 fissures, which is occasioned in them by the shrinkage of the mass, from 



