SOIL AND SUBSOIL. l8l 



nardino Valley of California has been thus brought about ; and 

 unfortunately this state of things is almost beyond the possi- 

 bility of remedy. 



Injury from Impervious Substrata. The injurious effects of 

 a difficultly penetrable subsoil have already been discussed and 

 are selfevident. When the substratum is a dense clay, the rise 

 of moisture from below being very slow, it can easily happen 

 that the roots cannot penetrate deep enough in time for the 

 coming of the dry season, and that thus the crop will suffer. 

 The case will be still worse when hardpan cemented by lime 

 or silex limits root-penetration, as. well as proper drainage. 

 In such cases the culture of field crops often becomes im- 

 practicable, even with irrigation, as its frequent repetition, be- 

 sides being costly, can rarely be commanded. In the case of 

 trees, the limitation of root-penetration results in the spreading- 

 out of the roots on the surface of the impenetrable layer; as 

 shown in figure 36, which exhibits a root-development that 

 \vould be quite normal in the regions of summer rains, but is 

 wholly abnormal in the arid region, and results in the unpro- 

 fitableness or death of the trees. It has often been attempted 

 in such cases to plant trees in large holes dug deep into the sub- 

 soil and refilled with surface earth and manure. All such at- 

 tempts result in failure, if only because the excavation in- 

 evitably fills with water, which will soak away but very slowly 

 into the dense substrata, and will thus injure or drown out the 

 roots. Besides, the latter will remain bunched in the loose 

 earth, and will thus be unable to draw either moisture or 

 nourishment from the surrounding land. It is absolutely nec- 

 essary to remedy this by loosening the substrata, if success is 

 to be attained. 



Shattering of Dense Substrata bv Dynamite. The per- 

 manent loosening of dense substrata is best accomplished by 

 moderate charges ( ' j to 04 pounds) of " Xo. 2 " dynamite at a 

 sufficient depth (3 to 5 feet). The shattering effect of the ex- 

 plosive will be sensible to the depth of eight feet or more, and 

 will fissure the clay or hardpan to a corresponding extent side- 

 wise. If properly proportioned the charge will hardly disturb 

 the surface; but if this he desired, from i ' jto j' j pounds of 

 black powder placed above the dynamite will throw out suffi- 



