CHAPTER V 

 GROUND- (UNDERGROUND) WATER 



Many familiar facts demonstrate the presence of abundant 

 water beneath the surface. The thousands of wells in lands peo- 

 pled by civilized man, and the many springs which issue from 

 the slopes of mountains and valleys are sufficient proof both 

 of the wide distribution of ground-water and of its great abun- 

 dance. 



Certain well-known facts make it clear that ground-water is 

 intimately connected with rainfall. The level of the water in wells 

 commonly sinks during droughts, and rises after rains; and the 

 sinking is greater when the drought is long, and the rise is more 

 notable when the rainfall is heavy. Many springs flow with reduced 

 volume in times of drought, and others cease to flow altogether. 

 Furthermore, rain-water is seen to sink beneath the surface, wher- 

 ever the soil is porous. Sinking through the soil to the solid rock, 

 it finds cracks and pores, and through them it descends to greater 

 depths. Nowhere are the rocks beneath the mantle rock so com- 

 pact and so free from cracks, when any considerable area is con- 

 sidered, as to prevent the percolation of water through them. The 

 conditions which influence the amount of water which sinks be- 

 neath the surface have been mentioned (p % 110). 



Supply of ground-water not altogether dependent on local rain- 

 fall. The amount of ground-water in a given region does not 

 always depend entirely on the local rainfall. Ground-water is in 

 constant movement, and entering the soil or rock at one point it 

 may, after a subterranean journey, reach a point far from that where 

 it entered. Thus beneath the Great Plains of the West there is 

 much subterranean water which fell on the eastern slopes of the 

 Rocky Mountains. It has flowed beneath the surface to the plains 

 where some of it is now drawn out for purposes of irrigation in 



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