THE WORK OF WATERS UNDERGROUND 113 



which it passes will come to equalize the pressure of the water 

 column, and no outflow will occur. Figure 104 shows a 

 typical flowing well of large volume. 



Artesian wells are common in parts of the Atlantic Coastal 

 Plain, the Great Plains, southern Wisconsin, northern 

 Illinois, and in many other places. Many cities such as 

 Savannah, Georgia, and Brooklyn, New York, whose wells 

 have a capacity of about 22,000,000 gallons per day, receive 

 much water supply from artesian wells. In parts of the West, 

 artesian waters are used extensively for irrigation purposes. 



Deep-seated springs. Ground water ascends to the 

 surface from relatively great depths through large cracks 

 or fissures in the rocks. 

 It rises by hydrostatic 

 pressure, as in the case 

 of flowing wells. Fig- 

 ure 105 illustrates the 

 occurrence of a deep- 

 seated spring and sug- 

 gests the intricate 

 courses through joints 



and Other cracks that Fio. 105. Diagram showing the intricate 

 Water which descends underground drainage which issues in a 

 . . deep-seated spring. (Geikie.) 



to considerable depths 



must follow before completing its underground circulation. 

 It moves down rather readily through the surface rocks, but 

 as it descends deeper the pressure of the column of water 

 behind it may force it toward the surface through any open- 

 ings it encounters which lead upward. Sinking again through 

 other cracks, it may follow a zigzag lateral course for a long 

 distance, moving repeatedly up and down before reaching at 

 last a fissure or other trunk channel through which it may 

 rise to the surface. 



Geysers. Geysers are hot springs that erupt at intervals. 

 Existing geysers are confined to areas of recent volcanic 

 activity in Yellowstone Park, Iceland, and New Zealand. 



