Book III. 



DRAINING BOGS. 



631 



other level is found to be in some places below that of the spring, and where, in boring in 

 this direction, water is not found to follow, it will be necessary to make short drains or cuts 

 of the same depth with the cross-drain, from it quite up to the source of the spring; for, 

 if the drain be cut below the line of the spring, the possibility of reaching it by means of 

 an auger is lost, as where the under stratum is clay, and there is no under water, the use 

 of the auger cannot be effectual ; and if it be made above the line of the spring, it will be 

 requisite to cut and bore much deeper, in order to reach it, the ground being in general 

 higher in that part : besides, the portion of porous stratum below the drain may contain 

 a sufficient quantity of water to render the land wet, and that may readily get down 

 underneath the trench, between the holes formed by boring, and break out lower down. 



3935. In situations where the extent of bog in the valley between tivo banks or eminences 

 is so narrow and limited as that the stratum of rock, sand, or other materials that contains 

 the water, may unite below the clay at such a depth as to be readily reached by the auger 

 {Jig. 487 a), it will seldom be necessary to have more than one trench up the middle, 



487 



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well perforated with holes (b) by means of the auger; cross or branching drains being 

 unnecessary in such cases. For notwithstanding the springs, that render the land inju- 

 riously wet in these cases, burst out of the banks or eminences on every side, for the 

 most part nearly on the same level, the reservoir from which they proceed may be dis- 

 covered in the middle of the valley, by penetrating with the auger through the layer of 

 clay, that confines and forces the water to rise up and ooze out round the superior edge of 

 it, where it forms an union with the high porous ground. From the drain being made 

 in the hollowest part of the land, and the porous stratum containing the water being then 

 bored into, it is obvious that the ditch or drain thus formed being so much lower than the 

 ordinary outlet of the springs, the pressure of water above that level, which is the bottom 

 of the drain, must be such as to force that which is under the drain or trench through the 

 holes made by the auger, and in nriany instances, until a considerable quantity of the 

 water is evacuated, make it rise to a greater height than the level of its natural outlet. 

 The effect of which must be, that the water forming the spring, having found by these 

 means a fresh and more easy passage, will quickly relinquish its former openings, and 

 thus be prevented from running over and injuring the ground, that previously lay lower 

 down than it. 



3936. But in swamps or bogs that are extensive and very wet, other drains or cuts than 

 such as convey off the springs must be made ; as, notwithstanding the higher springs 

 which chiefly cause the wetness may be intercepted, there may be lower veins of sand, 

 gravel, or other porous materials, from which the water must likewise be drawn off. In 

 cases of this nature, where the land is to be divided into enclosures, the ditches may be 

 formed in such directions as to pass through and carry off collections of water of this 

 kind, as well as those that may be retained in the hollows and depressions on the surface 

 of the land. There are in many places very extensive tracts of ground that are rendered 

 wet, and become full of rushes and other coarse plants, from causes of such a nature as 

 cannot be obviated by the making of either open or covered drains, however numerous 

 they may be. Lands in this situation are frequently termed holms, and mostly lie on th6 

 sides of such rivers and brooks as, from the frequency of their changing and altering their 

 courses between their opposite banks, leave depositions of sand, gravel, and other porous 

 materials, by which land is formed, that readily admits the water to filtrate and pass 

 through it to the level of the last-formed channels^ and which preserves it constantly in 

 such a state of moisture and \\'etness, as to render it productive of nothing but rushes and 

 other aquatic plants; and if a pit or ditch be made in lands under these circumstances, it 

 quickly fills with water to the same level as that in the watercourse. Tliis effect is, how- 

 ever, more liable to be produced, as well as more complete, where the current of fhe 



Ss 4 



