Book III. 



DRAINING. 



627 



accordingly as they may be circumstanced in respect to their situation, the nature of their 

 soils, or the materials by which the water is obstructed and detained in or upon them. 



3917. Where lands have a sufficient degree of elevation to admit of any over-proportion 

 of moisture readily passing away, and where the soils of them are of such an uniform 

 sandy or gravelly and uninterrupted texture, as to allow water to percolate and pass 

 through them with facility, they can be little inconvenienced by water coming upon or 

 into them, as it must of necessity be quickly conveyed away into the adjacent rivers or 

 small runlets in their vicinity. 



391 8. But tvhere grounds are in a great measure Jiat, and without such degrees of ele- 

 vation as may be sufficient to permit those over-proportions of moisture that may have 

 come upon them from the higher and more elevated grounds, to pass readily away and 

 be carried oft', and where the soils of the lands are composed or constituted of such 

 materials as are liable to admit and retain the excesses of moisture ; they must be exposed 

 to much injury and inconvenience from the retention and stagnation of such quantities 

 of water. Such lands consequently require artificial means to drain and render them 

 capable of affording good crops, whether of grain or grass. 



3919. Lands of valleys and other low places, a. well as, in some cases, the level tracts 

 on the sides or borders of large rivers and of the sea, must also frequently be subject 

 to great injury and inconvenience from their imbibing and retaining the water that may 

 be thus forced to flow up into or upon them, either through the different conducting 

 strata from the hills and mountainous elevations in the neighborhood, or the porous 

 materials of the soils. In these ways they may be rendered swampy, and have bogs or 

 morasses produced in them in proportion to the predominancy of the materials by which 

 the water is absorbed and dammed up, and the peculiarity of the situation of the lands in 

 respect to the means of conveying it away. 



3920. To ])erform properly the business of draining, attention should not only be 

 paid to the discrimination of the differences in regard to the situation of the lands, or 

 what is commonly denominated drainage level ; but also to the nature, distribution, and 

 depth of the materials that constitute the soils or more superficial parts of them, as upon 

 each of these some variety, in respect to the effects arising from water retained in them, 

 may depend. 



3921- Wetness of land, so far as it respects agriculture, and is an object of draining, 

 may generally depend on the two following causes : first, on the water which is formed 

 and collected on or in the hills or highei grounds, filtrating and sliding down among 

 some of the different beds of porous materials that lie immediately upon the impervious 

 strata, forming springs below and flowing over the surface, or stagnating underneath it ; 

 and secondly, on rain or other water becoming stagnant on the surface, from the retentive 

 nature of the soil or surface materials, and the particular nature of the situation of the 

 ground. The particular wetness which shows itself in different situations, in the forms 

 of bogs, swamps, and morasses, for the most part proceeds from the first of these causes ; 

 but that superficial wetness which takes place in the stiff, tenacious, clayey soils, with 

 little inclination of surface, generally originates from the latter. 



3922. The most certain and expeditious method of draining, in such cases, is that of 

 intercepting the descent of the water or spring, and thereby totally removing the cause 

 of wetness. This may be done where the depth of the superficial strata, and conse- 

 quently of the spring, is not great ; by making horizontal drains (fig. 483 a) of consi- 



derable length across the declivities of the hills, about where the low grounds of the 

 valleys begin to form, and connecting these with others (6) made for the purpose of con- 

 veying the water thus collected into the brooks or runlets (c that may be near. Where 

 the spring has naturally formed itself an outlet, it may frequently only be necessary to 

 bore into it (e) or render it larger, and of more depth ; which, by affording the water 

 a more free and optn passage, may evacuate and bring it off more quickly, or sink it to 

 a level so greatly below that of the surface of the soil, as to prevent it from flowing into 

 or over it. 



Ss 2 



