102 



THE PRINCIPLES OF 



is probably a clay bed some few feet beneath the surface ; 

 the water sinks until it can sink no further, and it then 

 begins to accumulate on the clay bed, and rises upwards 

 towards the surface. Possibly it may rise above the surface, 

 in which case we have a mere or marsh. Sometimes it rises 

 to within a few inches of the surface, in which case an im- 



FIG. 3. SHOWING SECTION WET FROM AN IMPERVIOUS SUBSTRATUM. 



A A the upward limit of water, or water table, causing a rank and coarse vegetation. 

 B the section water-logged, or super-saturated with water, c c retentive clay bed pre- 

 venting the escape of water. 



wholesome condition of soil is induced. At other times it 

 lies well beneath the surface, in which case we should have 

 a wholesome condition of soil. We have in these light soils 

 a section which has been properly called the section of super- 

 saturation, above the obstructive bed, or a section which 



