MOVEMENTS OF GROUND WATER 



359 



is given to rock (Fig. 225) when weak soluble parts are eaten 

 away, and stronger less soluble parts are left unchanged. 

 Granite, for example, 

 consists of more soluble 

 and less soluble materi- 

 als, and the rapid dis- 

 appearance of the solu- 

 ble parts and the per- 

 sistence of the more 

 resistant parts are re- 

 sponsible for the peculiar 

 shapes and forms noticed 

 in underground granite 

 rock. 



Ground water feeds 

 streams and rivers. 

 These finally make their 

 way to the sea. The 

 sea owes its saltiness 

 to ground water which 

 flows through rock con- 

 taining the constituents 

 of salt ; it owes its lime 

 to ground water which flows through rock containing lime. 

 Ground water yearly contributes to the sea millions of tons 

 of valuable mineral matter. 



Movements of ground water. Wells run dry and springs 

 sometimes cease to flow in dry seasons when rain does not fall. 

 The springs bubble forth again when the drought is broken 

 by plentiful rains and water returns to the wells. There 

 is a close relation between rain water and ground water 

 because ground water is water and snow which have sunk 

 below the surface. Rain sinks into the ground by means of 



FIG. 225. The work of water as a solvent. 



