554 DRAINAGE OF LAND FOR [Jan. 



with the help of a few plans, it is my endeavour to set forth in 

 this paper. 



Though a level may be of use in some cases to indicate the 

 direction of the fall of the ground, the eye will, as a rule, be a 

 sufficiently accurate test, and it may be useful to recollect in this 

 connection that a fall of six inches in the course of a mile will 

 create a flow at the rate of one mile per hour. In laying out drains, 

 possibly much may be done in improving and straightening 

 existing natural watercourses. Open or surface drains should 

 without exception be employed, unless the crossing of a road or 

 some such circumstance compel the construction of a covered 

 conduit : covered drains through the body of a plantation are in 

 every way objectionable. Those most generally made use of may 

 be enumerated as follows : — ]\Iain drain — sub-main — minor or 

 parallel — and spur, which is often of use in tapping the source of a 

 spring, or drawing off the moisture from an isolated spot which the 

 necessary regularity of the system employed has left untouched. A 

 judicious combination of these four varieties will seldom fail to draw 

 the surplus moisture from ground of the most irregular and com- 

 plicated formation. As to tlie dimensions of a main drain, the largest 

 amount of water ever likely to be carried into it from the slope, or 

 slopes on either side, according as the case may be, must be our 

 guide, but a main 36 in. deep, 12 in. to 18 in. wide at bottom with 

 an easy slope, so as to prevent falling in and consequent destruction, 

 will meet most ordinary requirements, though circumstances may 

 demand a larger channel. At any rate it is wiser to lean to the 

 side of over-capacity than the opposite extreme. 



At the foot of a slope, or wherever a depression or hollow exists, 

 with rising ground at one side or both (that is, supposing the 

 neighbouring ground requires draining), a main drain should be cut. 

 Now as to minor or parallel drains — which I take out of their order 

 for convenience' sake. They should be formed up and down the 

 face of the sloj)e if it be a moderate one, but more diagonally if it 

 be steep or at all precipitous, as otherwise the moisture wdll be 

 drawn away too speedily, and will carry with it the most valuable 

 particles of surface soil. Only the nature and dampness of the soil 

 can direct us to their depth and distance apart, but in a clay soil a 

 depth of 20 in., and width at bottom of 9 in., or in a lighter 14 in. 

 and 9 in. respectively, wall prove ample, while they should never be 

 placed more than between 40 ft. and 50 ft. apart, or less than 15 ft. 



Where slight hollows occur across the surface of a stretch of 

 ground requiring drainage, striking the course of the main at a right 

 or any oblique angle, a sub-main drain should be inserted, having a 

 communication with the main. In size it should be a mean between 



