Book III. 



DRAINING BOGS. 



633 



given to the forming of the ridges and giving them a regular descent towards themain 

 drain, which will contribute greatly to the assistance of the others in conveying off heavy 

 falls of rain-water when they occur. 



3939. But a necessary precaution previous to any attempt to drain lands of this kind 

 in the way that has been described, is to ascertain whether the porous stratum under the 

 clay be dry, and capable of receiving the water when let down into it ; or already so 

 loaded with moisture itself, as, instead of receiving more from above, to force up a large 

 quantity to the surface, and thus increase the evil it was intended to remove. This may 

 be the case in many instances, and the substratum contain water which affords no appear- 

 ances of wetness on the surface, at the place, on account of the compact body of clay that 

 is placed over it, but which, from its being connected with some spring that is higher, may 

 flow up when an opening or passage is given it, either by means of a pit or the auger. In 

 this way a greater quantity of water might be brought to the surface, which, from its 

 being confined by the surrounding banks, would render the ground much more wet than 

 before, and in particular situations produce very great degrees of wetness. When the 

 surrounding high ground declines lower than the bog, though it may be at a considerable 

 distance, by the aid of the level, and the appearance of the surface, the nature of the 

 stratum underneath may, in some degree, be ascertained ; and, notwithstanding it may 

 already contain water, a drain may be formed into it to carry off that water, and what 

 may likewise be let down into it from the retentive stratum that lies above it. It 

 must be confessed, however, that cases where surface water can be let down through a re- 

 tentive stratum to a porous one that will ac- 

 tually carry it off, are very rare. When these 

 occur, it is chiefly in limestone or coaly dis- 

 tricts, where the surface is hilly or rugged 

 {Jig. 489.), and more calculated for the pur- 

 suits of the mineralogist than the agricultor. 



3940. Draining hUli/ lands is not in gene- 

 ral attended with great expense, as the drains 

 need seldom be covered or filled up, only in 

 such places as may be sufficient for passages 

 for the animals to cross by. And though, 

 where the depth of the trench does not come 

 to the water confined below, it may be neces- 

 sary to perforate lower, there need not be any 

 fear that the holes will fill up, even where the 

 drain is left open ; as the impetuosity of the 

 water itself, will remove any sand or mud 

 that may fall into them, where much flood or 

 surface water does not get in. Small open- 

 ings may, however, be made along the upper 

 side of the trench, in ofder the more eflfectually to secure them against any obstructions ; 

 and in these the perforations may be made, leaving the mouth of the holes about six inches 

 higher than the bottom of the drain, which will be without the reach of the water that 

 may be collected during the time of heavy rains. 



3941. The sides or declivities of maiiy hills, from the irregularity of the disposition of 

 the strata that compose them, are often covered with alternate portions or patches of wet 

 and dry ground. By the general appearance of the surface and the vegetable products 

 that are grown upon it, the nature and direction of the internal strata may frequently be 

 ascertained with so much certainty as to determine the line or direction of a drain with- 

 out the necessity of examining below the surface of the land. As the ease or difficulty 

 of draining such grounds depends solely on the position of the different strata of which 

 the hill or elevation may be formed, and upon the erect or slanting direction of the rock, 

 or other retentive body in which the water is contained ; where the rock has a slanting or 

 horizontal inclination, the whole of the different springs or outlets, that show themselves 

 on the surface, may originate from or be connected with the same collection or body of 

 water, and may be all drained and dried up by cutting off, or letting out, the main body 

 of water, by which they are supplied, at the inferior part of the reservoir, or that part 

 where the water would of its own accord readily run off if it were not confined beneath an 

 impervious covering of clay or some other material. 



3942. But in cases where the rock lies in an erect or perpendicular form, and contains 

 only partial collections of water, in some of the more open cracks or fissures of the stone, 

 that discharge themselves at various openings, or outlets, that have not the least connec- 

 tion with each other, it would be an idle and fruitless endeavor to attempt the cutting of 

 them off by means of one drain {Jig. 490 a), or by boring into any one of them in par- 

 ticular, without cutting a drain into each (o, b, c). In this case it is more advisable to make 

 the main drain wholly in the clay, with small cuts made up to each outlet, than along the 

 place where the springs burst out ; as in that line of ditection it would be too greatly in 



W^^mm^ 



