136 



PRELIMINARY WORKS. 



indicated ; on firm soil it may be greater, on loose soil 

 smaller. 



The dcptli of the feeders depends on the depth to which it 

 is intended to drain the land ; the former must be somewhat 

 greater than the latter. The depth to which the soil requires 

 draining may vary from 18 inches to 3 feet, according to the 

 species to be grown. Ash, hornbeam, and elm can do with 

 18 inches, while Scotch pine, beech and silver fir, prefer soil 

 which is drained to a depth of 3 feet. 





u 



a, a. Natural level of ground. 



h. Feeder, four feet deep. 

 c, c. La}-er.s of soil actually drained. 



Fiff. 17. 



(/, (/. Layers of .soil not drained. 

 ( Id c. About three itet. 



Fig. IS. 

 a. a. Natural level of ground. 

 h, b. Leaders (five feet deep), or main drains. 



c, c. Feeders. Depth at upper end, 3 ft. G in., at lower end, 4 It. U in. 

 (In these diagrams tlie height is exaggerated.) 



Figs. 17 and 18 illustrate the comparative depth to which 

 a locality is drained, and that of the feeders and leaders. 



The sha2)e of the drains depends on the fall and on the 

 nature of the soil ; the greater the cohesion of the latter, the 

 steeper may be the slopes of the sides. In the case of peat, 

 the sides may be almost perpendicular, in stift' loam they 

 should I'urui an an<^ie oi' uljout 15 degrees, and they must 

 become more and more slanting, as the proi)ortiun of sand in 

 the soil increases. The base of the ditch should be at least 

 as broad as the spade which is used in making and after- 



