Book III. 



FORMATION OF DRAINS. 



707 



thirty-two feet from each other, across the fields from the different ditches, according to 

 the circumstances of the lands ; or, indeed, where the drains, either from some slight 

 imevenness of the surface, or other causes, can only be made to flow at one end, to 

 avoid cutting them further on one side than where the ditch is capable of taking away 

 the wetness. In cases where the declivities of a piece of ground are various, and have 

 different inclinations, the drainer should constantly attend to them, and direct the lines 

 of his drains in such a manner as that they may cross the higher sides of the different 

 declivities in a slanting direction. 



4280. IVie depth of drams must depend upon the nature of the soils, the positions of 

 the land, and a great variety of other more trifling circumstances. It was formerly the 

 custom to make them three or four feet in depth, but by modern drainers the most 

 general depth is two and a half to three feet. As the main drains have more water to 

 convey away, and are generally of greater length than the lateral ones, they should always 

 be cut somewhat deeper ; and where the materials of the soils are porous, the deeper 

 they are cut, the more extensively they act in lowering the wetness of the land : when, 

 however, the operator reaches any material through which the moisture cannot pass, it 

 will be useless to dig the trench to a greater depth. If it be clay, by going a few inches 

 into it, a more safe passage for the moisture may however be secured. It must notwith- 

 standing be invariably attended to, that the depth of the drains be such as that the 

 treading of heavy cattle may not displace, or in any way injure, the materials employed 

 in constructing or filling them. It may be noticed too, where the horses in ploughing 

 tread in the bottom of the furrow, at the depth of four inches or more below the surface, 

 that, if eight or ten be allowed for the materials with which the drains are filled, when 

 the depth of the trenches does not exceed twenty-four inches, there will only be nine 

 or ten inches of earth for the support of the horses when ploughing. Where the earth 

 has been stirred, such a depth must undoubtedly be too little, and this in some measure 

 proves that drains of such a depth are not sufficient. By cutting them down to the 

 depth of two feet and a half in the stiffer ; r.ils, they will seldom be penetrated to, or 

 have too great a depth ; and in the pervious ones a still greater depth is highly useful, 

 and constantly to be practised. 



4281. Cutting the drains as narrow as possible, which has of late been much practised, 

 is of importance, as it causes a considerable saving of the matters employed in filling 

 them up, whether wood or straw ; but in cases where bricks or stones are used, this 

 cannot be so much attended to; however, a greater width than about a foot is seldom 

 necessary, provided the stones be coupled at the bottom, or thrown in in a mixed way ; 

 nor more than sixteen inches where laid in the manner of a sough or cliannel. But of 

 whatever depth the materials may be, the earth or mould by which they are covered up 

 should not be less in depth than a foot ; in arable lands it should be more. 



4282. The different sorts of drains in use may be classed in two divisions ; drains of 

 conveyance {Jig. 643. a, b,) alone, and drains of conveyance and collection jointly. (Jig. 



643. c,d.) In the former, all that is neces- 

 sary is a channel or passage for the water, of 

 sufficient dimensions, which may be formed 

 by pipes of different kinds, arched or barrel 

 drains (b), and box or walled drains (a). The 

 construction of the latter requires not only 

 an opening for conveying the water, but a 

 superincumbent or surrounding stratum (e,f, ) 

 of sufficient porosity to permit and induce 

 all latent water to find its way to the channel 

 of conveyance. The most complete drain of 

 conveyance is a large pipe of metal, masonry, 

 or brick- work; and the most complete col- 

 lecting drain, one formed of a channel built 

 on the sides, and covered with flat stones, mth 

 superstratum of round stones or splinters, diminishing to the size of gravel as they rise 

 645 to the surface, and there covered with the 



common soil. As the best constructions, 



however, are not always practicable, the fol- 

 lowing are a few of the leading sorts adapted 

 fordifferent situations. 



4283 For drains of convei/ance, there are the walled 

 or box drain {fig. 643. a), the barrel drain (6), the 

 walled or the triangular drain (c), and arched drain. 



4284. brains of collection are formed of stone, brick, 

 gravel,cinders,wood, spray,straw, turf, and earth alone. 



4285. The boxed and rubble drain {fig. 644.) has been 

 already described as a drain of conveyance and col- 



z 2 



