The Supply and Uses of Water 195 



supply in the water-bearing layers, may give sufficient pressure 

 to cause the water to flow freely from the mouth of the well. 

 A well that flows thus is called artesian, from Artois, a province 

 in France. The water sometimes spouts to a great height; 

 in South Dakota an artesian well sent a jet more than ninety- 

 five feet high. If it were not for friction, the water would 

 rise in pipes almost to the level of the source of the supply ir 

 the water-bearing layers of earth. 



Artesian wells found in a plain or valley which slopes more or 

 less gradually from high land are made possible by the char- 

 acter of the different laj^ers of the earth's crust. Such condi- 

 tions are found along the Atlantic, Pacific, and Gulf coasts, and on 

 the Great Plains. Distance from the head of the water-bearing 

 layers and the character of the intervening surface are no barrier 

 to such a supply. Water drawn from wells at Calais, France, is 

 carried through porous rock layers from England under the 

 English Channel. Along the southern coast of New Jersey, as 

 at Atlantic City, artesian wells are supplied by water that comes 

 beneath the marshes from the mainland many miles away. 



The cross section (Fig. 58) of a wide valley with a river 

 cutting through it shows how the character of the surface and the 

 distance from the head of the water supply cannot affect deep 

 wells. The deep permeable strata, which supply the wells with 

 water, secure their supply in distant highlands. The surface 

 water is prevented from entrance into these porous layers by the 

 first bed of impermeable material. 



The water level of the ground moisture varies with the wet and 

 dry seasons ; it rises during wet weather and sinks to lower 

 levels during dry weather. The water level is just the upper 

 limit of water saturation of the ground, the height of water in 

 a surface well showing the local water level. This rises or falls 

 according to the rainfall. The general water level conforms with 

 the elevations and depressions of the land (cf. Fig. 58), but is 

 usually nearer the surface under depressions, such as valleys, 

 than under hills. It often reaches the surface and forms springs 



