Irrigation, — 109 



and if the subsoil is firm clay, or hard pan, it will be retained, 

 and as the surface soil dries, absorbed by capillary action, and 

 brought within reach of the roots of vegetation. 



" The connecting overflow trenches should be in the subsoil, 

 and filled with .fine stone to the depth of a foot at least, and 

 shingled with flat stones in the same manner as the reservoir 

 trenches. This shingling should be of sufficient depth to escape 

 the plough or the deepest spading. The head of the overflow 

 trenches at the base of the slope should be at least twelve or 

 eighteen inches above the bottom of the reservoir." 



Cross-section of slope thus subirrigated is presented in 

 engraving. A is the surface soil ; B, the reservoir trenches ; 

 C, the subsoil ; D, the connecting overflow trenches (which 

 might be laid with tile where that can be had conveni- 

 ently and cheaply), and E, the outlet of drainage trench. I have 

 given this for information more than in the expectation that 

 many readers will make practical use of it. 



