64 DOMESTIC WATER SUPPLIES FOR THE FARM 



considerable amounts of water, but are seldom used as a source of 

 supply. The water in the limestones is carried in definite chan- 

 nels and is of rather uncertain occurrence. Both the sandstones 

 and limestones yield copious springs in places. Wells in the syn- 

 clines or rock troughs frequently yield water which will some- 

 times rise to the surface, but in general dependence is placed on 

 the springs which occur in large numbers throughout the belt. 

 In the wider limestone valleys wells or cisterns are often used. 

 There are very few cities or large industrial establishments in 

 this region and deep wells are therefore somewhat rare. 



The Mississippi-Great Lakes Basin. - - This basin includes 

 the remaining portion of the territory in the eastern half of the 

 United States. The surface is moderately low, seldom exceeding 

 1000 feet in elevation, and is usually not characterized by promi- 

 nent hills or mountains. Except in the areas of igneous rocks, 

 noted above, the rocks consist of flat or very gently folded 

 sandstones, limestones, shales, etc., varying from Cambrian to 

 Carboniferous in age. The Cambrian and other of the older sand- 

 stones carry large amounts of water, which is obtained by wells 

 that frequently flow at the surface. The Silurian limestones also 

 contain considerable water, but, as is the case with water in lime- 

 stones elsewhere, its occurrence at a particular point can seldom 

 be predicted. 



The younger rocks, including the Devonian and Carbonifer- 

 ous, consist to a considerable extent of alternations of shales, 

 shaly limestones and sandstones. In the limestones the water 

 occurs very much as in other limestones. In the sandstones and 

 shales, however, its occurrence is uncertain owing to the lack of 

 persistence of the beds. One well may obtain water, while an- 

 other a few feet away may fail. The waters are often mineralized, 

 especially in Michigan, where they contain a high percentage of 

 salt. The Carboniferous limestones abound in springs, some of 

 which are of great size. 



The High Plains. Stretching eastward from the flanks of 

 the great Rocky Mountain range and underlying large portions of 



