88 A MANUAL OF FORESTRY. 



disturb the sand. "When the area has been stocked with 

 trees, clear cuttings must be strictly avoided, the wood 

 being treated under the selection system, else the work 

 may have to be done over again. 



6. Fixation of Unstable Soil on Slopes. 



Owing to the action of water, soil on sloping ground 

 may become unstable. Water filtering downwards 

 causes a reduction in the cohesion of the different 

 layers of the soil, followed by gradual denudation, 

 or landslips. In water-channels the banks may be 

 undermined. The result is a reduction in the pro- 

 ductive power of the slopes, while the level ground 

 below may be covered with the debris brought from 

 above ; at any rate the water-channels in the low land 

 silt up, and give rise to inundations. 



The detailed consideration of this subject belongs to 

 Forest Protection. It will suffice here to state that the 

 best preventive measure consists in keeping such ground 

 permanently under forest growth, from which domestic 

 animals should be excluded. 



If a bare area exposed to denudation is to be wooded, 

 it may be necessary to fix the soil before sowing or 

 planting be attempted. This is done by regulating 

 the existing water-courses, terracing them, and even 

 erecting wooden or masonry revetments. Where neces- 

 sary j additional water channels must be cut to lead off 

 all surplus water into the regular channels. Cattle of 

 all kinds must be strictly excluded. The land itself 

 may have to be terraced, or wattle fences may be erected 

 at suitable intervals. Only after the soil has been 



