134 



FIRM SUBSOILS. 



inches in depth, and from which the roots draw all 

 their nourishment ; (6) is an iippervious stratum, 



or very firm subsoil, which the roots can hardly 

 enter, and the noxious gases which it contains are 

 poisonous, because the air does not gain admittance 

 to it. Not only does this stratum retard the ex- 

 tension of the roots downwards, but it prevents any 

 benefits from accruing to the surface-soil from the 

 drainage below ; (c) represents the underlying 

 stratum, which was formerly filled with stagnant 

 water. This was removed by the drains, and would 

 add a fine and inviting field to the roots, if the 

 impervious stratum could be broken up, and the 

 air gain admittance ; (d) shows the position of the 

 drains, which have performed their work, and yet 

 the cultivator is dissatisfied because they do not, on 

 account of this hard subsoil, prevent the evil efi"ects 

 of drought. Thus, when a dearth of rain occurs, it 

 can be readily seen that the surface-soil must be- 



