CHAPTER IV. 

 GROUND WATERS AND THEIR OCCURRENCE. 



Derivation of Ground Waters. Practically all of the water 

 in the soil and rocks is of meteoric origin; that is, it is de- 

 rived from rainfall. In fact, many who have written on under- 

 ground waters have stated that rainfall is the only source of supply. 

 In reality, however, while rainfall probably contributes at least 

 99 per cent of the total subterranean water, there are several 

 other possible sources of such water. 



Of the small percentage of water derived from sources other 

 than rainfall a small quantity is " magmatic water," or that given 

 off by molten rocks (magmas) at great depths; but, although con- 

 siderable additions may be made locally to the underground 

 water body in this way at points of igneous activity, the ad- 

 ditions to the supply in the earth's crust as a whole are insignifi- 

 cant. 



It is also a well-known fact that along coasts of unusually 

 porous materials such as certain coarse sands and coral or other 

 porous limestones, especially when the rainfall is light, the sea 

 water may penetrate through the pores of the rocks for a con- 

 siderable distance inland; but, the amount, although somewhat 

 greater than the magmatic waters, is very small. 



The greater part of the non-meteoric waters appear to rep- 

 resent sea waters included in marine foundations that have been 

 subsequently uplifted and converted into land. By far the larger 

 portion of the sedimentary deposits, including sandstones, shales, 

 limestones, etc., were originally laid down along the borders or 

 beneath the surface of the ocean, and were, of course, originally 

 saturated with salt water. It is probable that this water was 



often retained in the materials when they were uplifted and con- 



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