Book III. 



DRAINING RETENTIVE SOILS. 



635 



of impervious clay, which keeps up the water that is contained in the sand, and which, 

 being constantly full, renders the adjacent clay moist, and in wet seasons runs or trickles 

 over it. As in these cases, the principal under-stratum of clay is rarely above four or 

 five feet below the surface, a drain (^i^. 492 a\ is advised to be cut to that depth through 

 the middle of the field, if it have a descent from both sides ; but if it decline all to one 



side, the drain must be made in that place (/>), as the water will more readily discharge itself 

 into it; and, unless the field be of great extent, and have more depressions or hollows in 

 it than one, one drain may be quite sufficient for the purpose, as by crossing the different 

 beds that retain the water, it must take it off frdm each of them. 



3947. A principal difficulty in draining ground of this nature, and which renders it 



493 



impracticable by one drain, is when the direc- 

 tion of the alternate layers, or beds of clay and 

 sand, lie across the declivity of the land {Jig- 

 493 a, a), so that one drain can be of no other 

 service than that of conveying away the water 

 after it has passed over the different strata, and 

 would naturally stagnate in the lowest part of 

 the field, if there was no other passage for it. 

 Where the land lies in this way, which is fre- 

 quently the case, it will therefore be necessary, 

 Ijesides the drain in the lowest part [b), 

 to have others cut up from it in a slanting di- \ 

 rection across the declivity (c, c), which, by 

 crossing all the different veins, or narrow strata 

 of sand [d, d, d,), may be capable of drawing 

 the water from each of them. 



3948. Injhrming the drains in these cases, it is 

 recommended that,after laying the bottom in the manner of a sough, or in the way of a trian- 

 gle, it be filled some way up by small stones, tough sods being applied, the green side down- 

 wards upon them before the mould is filled in. But where stones cannot be readily pro- 

 cured, faggots may be employed in their place where they are plentiful : the under part 

 of the drain being laid, or coupled with stones, so as to form a channel or passage for 

 the conveyance of the water that may sink through the faggots, and for the purpose of 

 rendering them more durable ; as where the water cannot get freely off, which is gene- 

 rally the case where there is not an open passage made of some solid material, it must, 

 by its stagnation, soon destroy the faggots, and choke up the drain. 



Sect. IV. Of the Methods of draining Retentive Soils. 



3949. The practical mode of draining retentive soils, is materially different from that 

 which has been described above. Many tracts of level land are injured by the stagna- 

 tion of a superabundant quantity of water in the upper parts of the surface materials, 

 which does not rise up into them from any reservoirs or springs below. The removal 

 of the wetness in these cases may, for the most part, be effected without any very heavy 

 expense. From the upper or surface soil in such cases, being constituted of a loose 

 porous stratuiu of materials, to the depth of from two to four or five feet, which has a 

 stiff retentive body of clay underneath it, any water that may come upon the surface from 

 heavy rains, or otiier causes, readily filtrates and sinks down through it, until it reaches 

 the obstructing body of clay which prevents it from proceeding ; the consequence of 

 which is, that the porous open soil above is so filled and saturated with water, as to be of 

 little utility for the purpose of producing crops of either grain or grass. Land situated 

 in this way, is frequently said by farmers to be wet-bottomed. In order to remove this 

 kind of wetness, it seldom requires more than a few drains, made according to the 

 situation and extent of the field, of such a depth as to pass a few inches into the clay, 

 between which, and the under surface of the porous earth above, there will obviously be 

 the greatest stagnation, and consequently, collection of Abater, especially where it does 

 not become much visible on the surface. In these cases there is not any necessity for 

 having recourse to the use of the boring instrument, as there is no water to be dischaiged 

 from below. 



3950. IFhen the field to be drained has only a slight declination, or slope, from the sides 

 tojoards the middle, one drain cut through the porous superficial materials into the clay. 



