RECLAMATION OF THE SOIL. 21 





5. Fixation of shifting sand. 



C. Fixation of unstable soil on slopes. 



It would require a volume to itself to deal exhaus- 

 tively with these matters ; hence, in this place, only a 

 few short remarks can be made on the more important 

 points. Those who require more detailed information 

 will find it in special works on the several subjects. 



1. Treatment of an Impermeable Substratum. 



Impermeable strata in the soil consist in some cases 

 of an accumulation of clay, which has by degrees been 

 washed out of the surface layers and deposited at a 

 certain depth ; in other cases, sand or gravel has been 

 converted into a hard rock-like mass by the addition of 

 organic matter, clay, or oxide of iron. Such a stratum 

 is frequently called a pan. It may be found at varying 

 depths below the surface ; if at a depth of 4 feet or 

 more, it does not, as a rule, interfere with the growth of 

 forest trees, except perhaps on arid unirrigated ground, 

 but if it occurs nearer the surface it may produce the 

 following injurious effects : 



(a.) Interference with the development of a proper 

 root system, followed by small height-growth 

 and liability of the trees to be thrown by 

 strong winds. 



(b.) Interference with the movement of water in the 

 soil, preventing its penetration into the sub- 

 soil during wet weather, and its ascent during 

 dry weather ; in other words it may render 

 the soil too wet at one time and too dry at 

 another. 



