358 



THE WORK OF RUNNING WATER 



are the Hot Springs of Arkansas and Saratoga Springs, New 

 York. In 1910 about 60,000,000 gallons of water were taken 

 from mineral springs in the United States and sold for over 

 $6,000,000. Springs which contain iron, sulphur, and mag- 

 nesium are thought to have a beneficial effect on the body and 

 are called medicinal springs. Vichy in France, Hunyad in 

 Hungary, and Karlsbad in Bohemia are well-known medicinal 

 springs. 



The destructive action of ground water. Water is a de- 

 structive agent. It forms underground caves and caverns by 

 dissolving and carrying away in solution large masses of rocks. 

 It makes rock porous and weak by removing soluble materials 



and leaving pores and 

 cavities in the insoluble 

 g 1 portions, and it causes 

 rock to crumble into sand 

 and gravel. Limestone 

 is so readily soluble in 

 water containing carbon 

 dioxide in solution, that 

 numerous holes and 



FIG. 224. Showing how caves and holes are 

 formed by the solvent action of water. 



cavities are eaten out of it and after a long time caverns are 

 formed. Mammoth Cave of Kentucky and Wyandotte Cave 

 of Indiana are caves formed in limestone by the solvent action 

 of ground water (Fig. 224). The thinned and weakened roofs of 

 oaves sometimes fall in and dangerous sink holes are formed. 

 Where these holes are numerous land cannot be cultivated or 

 used for pasture, and is worthless to the farmer. 



Sandstone and conglomerate through which water flows 

 lose their cementing materials and crumble into sand and 

 gravel. Rocks are not equally soluble in water; some, like 

 limestone, are easily soluble, others are so little soluble that 

 there is no perceptible change in years. A peculiar appearance 



