GROUND-WATER 



211 



brought to the sea by springs and rivers, many shell-bearing animals 

 of great importance, geologically, would perish. Biologically, there- 

 fore, as well as geologically, ground-water is of great importance. 



SPRINGS 



Springs. The term spring is applied to any water which issues 

 from beneath the surface with sufficient volume to cause a distinct 

 current. If the water issues so slowly as to merely keep the surface 



Fig. 171. South face of Landslip Mountain, Colo. The protruding mass 

 on the right has slumped down. (U. S. Geol. Surv.) 



moist, it is not called a spring, but seepage. The spring from which 

 water issues with a strong current, especially if it is upward, is 

 comparable to a flowing well, while the spring from which water 

 issues with little force, and without upward movement, is com- 

 parable to the flow of water into a common well. 



Springs often issue from the sides of valleys (Fig. 172), the 

 bottoms of which are below ground-water level. They are especi- 

 ally likely to issue at the surface of relatively impervious layers, 



