36 PRACTICAL FORESTRY. 



unfortunately, only too evident in those areas drained 

 some few years ago, when the reverse was the opinion. 



The forester, by trial holes, should find out for 

 himself the exact distance suitable to the soil he is 

 draining ; but the following figures may assist him : 

 Strong clays - 4 to 6 times the depth. 

 Loams - 6 8 



Light loams - 8 10 



If the surface soil is rendered wet by springs, these 

 springs should be tapped by an auger, and the water 

 thus tapped carried off by the drains. 



On low-lying land where an outlet is difficult to 

 obtain, the drainage may be secured by digging a hole 

 through into the underlying rock, and draining into 

 it ; but this can only be successfully carried out where 

 the rock or substratum is porous. 



The depth of the sub-mains should be always 

 6 inches deeper than the minor drains, so as to permit 

 of a fall of water into them, which gives an increased 

 impetus and secures the washing away of impediments. 

 If they flow in on the same level there is a tendency 

 to stagnation throughout the whole system, without 

 the fall is considerable. 



Another matter of importance is the arrangement 

 of the minor drains. They should be so laid out that 

 they run with the greatest slope, and discharge alter- 

 nately into the main. If they discharge opposite one 

 another, the ctibris brought down by one is likely to 

 choke the other ; whereas in a correct system each 

 drain in the upper reaches, so to speak, should assist 

 the flow of the next, and so on, thus securing a 

 uniform flow throughout. 



