DRAINAGE. 
93 
soil or subsoil, as it is called, may be of tbe 
same kind as that above it, or it may be part of 
a large bed of clay, sand, gravel, or some other 
rock. 
3. If the top-soil be chiefly sand or gravel the 
water can readily drain through it ; but with a stiff 
Soil. 
Subsoil. 
Bock, 
Section showing General Formation of Ground. 
soil, that will not let the water pass freely, the land 
becomes sodden. 
4. Even when the water has passed into the 
ground, it may be stopped by the subsoil, and by 
that means, also, the surface-soil may be kept too 
wet. You know that if we dig into the ground we 
find standing water; it may be not far down, or 
it may be at a great depth; its distance below the 
surface depends on the kind of soil, and on the 
