410 



A TREATISE ON METAMORPHISM. 



meters from the surface. It is especially likely to be near the surface in 

 regions where there is abundant precipitation and a thick layer of drift 

 or a thick layer of disintegrated rocks. In elevated and irregular regions, 

 especially those in which the precipitation is rather small, the level of 

 ground water is frequently 30 to 90 meters below the surface, and in high 

 desert regions the level of ground water may be 300 or more meters below 

 the surface. 



The above general statements may be illustrated by various regions of 

 the United States. In the humid regions of eastern United States the level 

 of ground water varies from to 27 or 30 meters below the surface. 

 Throughout the greater part of the drift-covered region the sea of ground 

 water is penetrated at a depth of less than 15 meters, although on the 

 higher drift hills the level of ground water may be from 15 to 30 meters 



Fig. 5. — Relations of level of ground water to topography and to surface drainage. Lines with aTrows are lines of flow. 



After King. 



below the surface. For the disintegrated regions of the southern Appa- 

 lachians, water is generally reached at a depth of less than 30 meters. For 

 the greater part of the Coastal and Gulf plains water is ordinarily found at 

 a depth of less than 15 meters. In the high limestone region of Kentucky 

 and Tennessee the level of ground water may be 60 to 90 meters below the 

 surface. For the major portion of the western part of the great plateaus 

 east of the Cordilleras the level of ground water is from 30 to 75 meters 

 below the surface, although adjacent to the streams it is less than this." In 

 the arid regions cut by deep canyons the level of ground water may be 

 far below the surface. In portions of such regions it is so deep that some 

 authors have concluded that water wholly fails. But that this is not so is 

 shown by the numerous springs which issue in these regions along the 



« Darton, N. H., Preliminary report on the geology and water resources of Nebraska west of the one 

 hundred and third meridian: Nineteenth Ann. Kept. TJ. S. Geol. Survey, pt. 4, 1899, pi. ex. 



