300 GENERAL SCIENCE 



as that involved in the artesian well, in which a bored 

 hole takes the place of the fissure crack. 



Caves and caverns are often formed by the dissolving 

 of the mantle rock, such as limestone, by the ground 

 water. The Mammoth Cave in Kentucky, Luray Cavern 

 in Virginia, and Wyandotte Cave in Indiana are good 

 examples of this action of ground water (Figure 257). 



Work of Ground Water. -- The greatest work done by 

 ground water is due to its power of dissolving other sub- 

 stances. Some of these substances water dissolves easily, , 

 while others are dissolved only after the water has become 

 charged with carbon dioxide as it does in passing through 

 decaying vegetation. If it were not for this power that 

 water has of dissolving all substances, life would be 

 impossible. Plants and animals are dependent upon their 

 circulations, which are simply currents of water in the form 

 of sap or blood, carrying food in solution to the different 

 parts of their being. The foods that plants take from the 

 soil must first be dissolved. The same is true of the food 

 of animals ; it must be dissolved before it can be used by 

 the body. 



Water is also a great distributing agent. It distributes 

 food to plants and animals on land and sea. It aids in the 

 distribution of heat through the agency of ocean currents, 

 and it distributes material for the building of sedimentary 

 rocks on the ocean floor. 



River Formation. -- The water that falls as rain and is 

 neither evaporated nor absorbed by the soil collects in 

 little streams and runs off toward the sea. Along its 

 course it is joined by other surface streams and also by 

 underground streams and the water from springs until it 

 is large enough to be called a river. A river is simply a 

 large stream of water which is bearing the run-off water 



