Book III. DRAINING MIXED SOILS. 699 



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 vv^hich 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. 



4248. 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, 

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

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

 them off by means of one drain (Jig. 631. a), or by boring into any one of them in 

 |^J|l:C:f g32 particular, without cutting a 

 ^^^^^ * a drain into each (o, 6, c). In 

 fl^jfl; ?^^^^^^ z*^^ *^*^ ^^^^ ^* ^^ more advisable 

 p:-S:^g::^j^y-v^VjW/^'^%^Q^^ to make the main drain wholly 



1 ^^<^ ^ ,j^ in the clay, with small cuts 



^^^^p^^^|^^^^^^^^^^^^'*"'^L|Jri*,^^^ c made up to each outlet, than 

 y-^fl^^^V^'-^":it^aisr^^ii& ~~^/^ along the place where the 



{ ^'*^^*^^^^ MB^!ry>rrrrrrrrJX _p springs burst out ; as in that 



^ - ^ ^ = line of direction it would be 



too much in the rock, and consequently be extremely difficult to cut, on account of the 

 nature and disposition of the stone. When the water passing out on the line of the 

 springs can be found by the auger in the main drain, at the point of junction, it will 

 be the more completely cut off; but where this is not practicable, the depth of the 

 Small cuts may reduce it to such a level as will prevent its flowing over and injuring the 

 surface of the land below it. 



4249. In such hills as are constituted of alternate strata of rock, sand, and clay, the 

 surface of the last may frequently be wet and swamp, while that of the sand is dry, 

 and capable of producing good crops of grass ; in all such cases, in order to drain the 

 land completely, as many cuts will be necessary as there may happen to be divisions of 

 wet and dry soil. The summit, or most elevated part of such hills, being mostly formed 

 of loose porous materials, the rain and other water descends through it till its passage 

 becomes obstructed by some impervious bed or stratum, such as clay, when it is forced 

 up to the surface, and runs or oozes over the obstructing stratum ; after having 

 overflowed the upper clay surface, it is immediately absorbed and taken up by the suc- 

 ceeding porous one, and, sinking into it in the same way as before, passes out again at 

 the lower side, rendering the surface of the next clayey bed prejudicially wet, as it had 

 done that of the first. In this way the same spring may affect all the other strata of the 

 same kind, from the highest part down the whole of the declivity, and produce in the 

 bason, or hollow at the bottom, a lake or bog, should there not happen to be a passage 

 or opening to take away the water. In order effectually to drain hills of this kind, it 

 will be most advisable to begin by forming a trench along the upper side of the upper- 

 most rushy soil, by which means the highest spring may be cut off; but as the rain and 

 other water that may come upon the next portion of porous soil may sink down through 

 it to the lowest part, and produce another spring, a second cut must be made in that 

 part, to prevent the water from affecting the surface of the succeeding clayey bed. 

 Similar cuts must be formed so far down the declivity as the same springs continue in 

 the same way to injure the land, and in some cases a sufficiency of water may probably 

 be obtained to irrigate the land below, or for some other useful purpose. 



Sect. IV. Methods of draining Mixed Soils. 



4250. IFhere the soil is of a mired and varied nature, but the most prevailing parts of 

 the clayey kind, the business of draining is considerably more tedious and difficult than 

 where the superficial and internal parts have greater regularity. In such lands, as the 

 collections of water are completely separated by the intervening beds of clay, each 

 becomes so much increased in the time of heavy rains, as to rise to the level of the sur- 

 rounding surface ; when the water, finding a free passage, as it would over the edges of 

 a bowl, overflows and saturates the surface of that bed of clay, rendering it so wet and 

 sour that its produce becomes annually more scanty, and the soil itself more sterile and 

 unproductive. 



4251. From the sand-beds {fig. 632. a, a, a) in such cases having no communication 

 with each other, it must evidently require as many drains {b, b, b) as there are beds of this 

 kind, in order fully to draw off the water from each of them. A drain or trench is 

 therefore recommended to be cut from the nearest and lowest part of the field intended 



