104 



OPERATIONS OF DRAINING. 



fig. 6, which represents a section of the ground from C 

 toD. 



Fig. 7. 



'' When water is, in like manner, percolating through 

 one of these pervious strata, and meets with any obstruc- 

 tion, as a rock or bed of clay, (A, fig. 7,) it is stopped 

 in its progress, and, by the pressure of the water from a 

 higher source, it is forced upwards, and thus saturates the 

 superjacent soil, as from D to E, forming springs or a 

 general oozing. 



" In either of these cases, and they are the most fre- 

 quent that occur in practice, the object of the drainer is 



