186 On Draining. 



cipal strata that resist the admission of water, and are thence 

 termed impervious. It is evident, therefore, that springs must 

 originate from water falling, in the shape either of rain or 

 dew, or of melted snow and hail, upon such porous and 

 absorbent bodies ; and that the water subsiding down- 

 wards, until it is obstructed in its passage by these impe- 

 netrable substances, forms reservoirs of considerable mag- 

 nitude, which afterwards burst forth in all those different ap- 

 pearances which are met with. Thus springs are formed, 

 the strength of which depends upon the extent of high ground 

 which receives and retains the rain-water, the size of the re- 

 servoirs, and the supply they furnish. 



5. Back-water. A frequent cause of wetness is, the stag- 

 nation of water in the ditches that surround fields, particu- 

 larly such as lie in the upper side of the inclosure, where 

 the water, being confined, finds its way downwards into the 

 open parts of the subsoil, and oozes out to the surface, form- 

 ing, in wet weather, all the appearances of, and producing 

 nearly the same effect as, a natural spring. Water con- 

 veyed in a drain, or small stream for mills, or confined in a 

 mill-dam, or pond, has often the same effect. Where this 

 happens in drains, the stagnant water should be removed, 

 by giving more depth or declivity to the ditch in which it 

 lies. Where a dam occasions the mischief, a cut should be 

 made on its lower aide, to intercept any water that may ooze 

 through it. Old marl-pits full of water, and cattle-ponds 

 improperly constructed, sometimes occasion this sort of mis- 

 chief. 



6. floods from Rivers, Lakes, or the Sea. In these cases, 

 the proper remedy is embanking, to be afterwards explain- 

 ed, (Sect. II). But, in that case, the aid of machinery, is 

 often necessary to assist in the drainage. 



3. The Sorts of Drains commonly used. 



There are four sorts of drains : 1. The open ; 2. The co- 

 vered ; 3. The arched ; and, 4. The vertical, or pit-drain. 



1. Open Drains, or Ditches. These often answer the 

 double purpose of conveying superfluous water, and of in- 

 closing the fields ; though they certainly make a hazardous 

 and inconvenient sort of a fence, without the addition of a 

 bank, a wall, a hedge, or a railing. 



In cultivated land, where the ridges are of a proper length, 

 breadth, and height, and the furrows of an adequate depth, 

 and skilfully directed, much surface-water may thus be car- 



