io8 DOMESTIC WATER SUPPLIES FOR THE FARM 



Location of Deep Wells. In the location of deep wells the 

 chief consideration is the obtaining of a supply, slight differ- 

 ences in location seldom seriously affecting the cost, while the pre- 

 vailing use of casing in soft deposits insures safety from ordinary 

 sources of pollution. The occurrence of deep waters depends on 

 the character and structure of the rocks far below the surface. 

 No indications of these features are usually found at the surface, 

 and the well may as a rule be located independently of surface 

 relief, though where artesian flows are expected the well should be 

 located on as low ground as possible. Information as to the best 

 location for a deep well may often be obtained from a careful 

 study of the records of wells in adjacent regions, which can be 

 made by the more experienced and intelligent drillers, or from a 

 study of the rocks and their structure, which often requires the 

 services of a trained geologist. 



Relation of Depth and Supply. It is a widespread, in fact an 

 almost universal, belief that the amount of water increases with 

 depth and that water may be had anywhere if one only "goes 

 deep enough." This is, however, far from the truth. Rainfall 

 appears to be the source of at least 99 per cent of the freshwater 

 found in the ground, the remainder being water included in the 

 rocks at the time of their accumulation beneath the sea, to- 

 gether with a small amount derived from volcanic sources. As 

 would be expected from its atmospheric source, water actually de- 

 creases rather than increases in amount with depth, a great many 

 rocks encountered by the deeper wells and mines, especially at 

 depths below 1000 feet, being entirely destitute of water. 

 |f However, if only the more superficial portion of the crust is 

 considered, there is in general an increase of water with depth. 

 Except in valley bottoms and other depressions the surface soil 

 and rocks, although carrying much moisture, are rarely saturated; 

 but at depths which vary, according to climate, soils and topog- 

 raphy, from a few to several hundred feet, a saturated zone con- 

 stituting the ground-water body is encountered. Wells starting 

 anywhere above drainage level will in general encounter water in 



