Oil Drainhuj. 
417 
U])on land with a consklei-ablo slope, or if the clay subsoil 
contracts but little, 14 to 18 feet is not too near; but, as no gene- 
ral system can be laid down for draining clay land applicable 
to all localities, it must in many instances be determined by the 
Superintendent what depth of the drains, and space between them, 
will be sufficient to admit the free infiltration of water on land 
with a considerable slope. The course of the water to the drain 
on such lands is much longer than on level land, as shown by the 
Figs. 2, 3. 
Fig. 2. 
The drawing in Fig. 2 shows the fissures or cracks as they 
appear in dry weather on the surface of the land, a a the drain, 
b the ridge, and the black line from the ridge each way to- the 
drains is intended to show that the water in its passage through 
the fissures or cracks (allowing for the zigzag course of the fis- 
sures) flows direct from the ridge to the drain on level land. 
