38 



GARDEN MANAGEMENT. 



soil is obtained 



D 



On the proportion of each of these substances contained in 

 the soil and subsoil, therefore, will de- 

 pend the extent of drainage requisite. 

 Supposing that the land to be drained is 

 surrounded on two sides by high ground, 

 the soil of which is a retentive clay, but 

 which is known to be supeiposed on a 

 bed of sand or gravel, it is obvious that 

 in order to render the drains, D B D, 



effective, it will benecessar}' to pierce the stiff clay in order to carry the sm-plus 

 water into the looser soil P S. This is done by draining B by means of the 

 drains s S S in the usual way ; but at their outfall, or lowest part, the clay R C 

 is pierced by an auger, and a passage made for the water into the gravelly 

 stratum P S. 



98. Another case, of not very uncommon occurrence, arises when a loose 

 sandy or friable soil rests on a substratum of clay. Here all the moisture not 



taken up by evaporation is either 

 diffused through the gravel or 

 absorbed into the tenacious sub- 

 soil, from which it has no escape 

 thi-ough the soil PiC. Sinlving a 

 drain to the bottom of the soil 

 will not here serve the purpose, 

 unless it is sunk sufficiently deep into the subsoil R C to remove the moisture 

 absorbed at the surface of the substratum, although a false economy, and 

 the advice of ignorant workmen, might recommend such a course. 



gg. In another case, nearly resembling the above, where a jDorous soil rests 

 on stiff tenacious subsoil, R S, but crops out, or terminates, in a gravelly porous 



soil, having no power to retain 

 water, it is evident the water 

 '"^T)^ xx would follow the surface of the 



,. -^ retentive soil, in the direction of 



^.^ the arrow. To obviate this, a 

 main • drain is required at D, which 

 ^- will intercept and carry off the 



water from the porous soil P S. 



ioo. In the neighbourhood of rivers it is not unusual to find a retentive soil, 

 R S, rendered wet and spongy by the presence of land-springs, S 1, S2, S3, which 



force themselves up through the 

 retentive soil by capillaiy attrac- 

 tion. In this case, a drain should 

 be cut through the retentive soil 

 below the lowest spring, S 1, which, 

 however, is to be ascertained by 

 closely watching the moisture in the dry season. 



