MECHANICAL PREPARATION OF SOILS. 39 



loi. The materials employed in covering- drains are very varied, — brusli- 

 ■wood, rubble, stones, bricks, and pipes being all in use ; and in clay countries it 

 has been not imusual to form pipes with the clay itself, by inserting an arched 

 framework of wood, and withdrawing it when consolidated. The best and 

 cheapest drains, however, are drain-pipes, which are now obtainable every- 

 where en moderate terms, 



102. The implements used in drainage are a spade, or, in deep draining, 

 and in a clay soil, a series of two or three sj)ades, varying in size, and each 

 sloping to the point, and slightly rounded, so as to make a circular cut ; a 

 spoon-like implement for lifting the loose soil clear out of the bottom of the 

 trench ; and a level, which may easily be formed by fixing three perfectly 

 straight-edged boards in an upright position and in a triangular form, held 

 together by a vertical board in the centre, with an opening at its base for a 

 line and plummet. 



103. Having everything prepared, and a well-devised system laid down, which 

 should include the depth and size of the drains, as well as their distance from 

 each other, — considerations which wili depend on the nature of the soil and 

 subsoil, — two points, however, which continue to be a question of great doubt, 

 the advocates of deep drainage in heavy soils contending, that water will 

 find its level, which is in the bottom of the drain, through holes and crannies 

 innumerable ; and that the deeper the drain the wider is the area affected ; on 

 the other hand, it is contended, that while this doctrine is founded in truth, 

 it has its limits, and that beyond a certain dej^th the influence of the drain is 

 lost. A sort of compromise has been the result, and very deep drainage has 

 been nearly abandoned. On this subject the views expressed by our contributor, 

 3Ir. Chitty, in the following remarks, probably express the opinion of the ma- 

 jority of practical men. " Observe," he says, "that the depth should vary with 

 the nature of the soil. If the subsoil is a stiff retentive clay, care should be taken 

 to go no deeper than is necessary to be out of the way of the spade in digging and 

 trenching, or to give the necessary fall ; for every ground workman knows that 

 water does not readily filter through clay, and draining land is for the purpose of 

 drawing the water quickly off the surface, to prevent stagnation, and to admit of 

 going on it immediately after rain ; therefore, to lay drains so deep into the clay 

 that water would be weeks in filtering to them, would be the height of folly. If 

 the ground be more porous, let the drains be three, but not more than fom-, 

 feet deep. Having got the trenches ready, lay in the pipes, and cover them 

 for a few inches with rough porous rubbish, or broken crockery, or any such 

 material, and the drains will be effective and permanent^ The mode I prefer 

 is to lay soles or flat tiles, and on these to set half-jDipes or bridge-pipes, which 

 are of a tunnel-shape, and on these to lay the rough stuff, and fill in with 

 earth, which should not be rammed or trodden very tight, but allowed to 

 settle. If the trenches are merely filled with rough stuff to the thickness of 

 a foot or so, it will be effective, but not so permanent ; even brushwood will 

 do, and sometimes last for many years in clay soils." 



104. The drain shown in Jig. A is cut through a stratum of porous soil for 



