114 A YEAR IN SCIENCE 



water is carrying along. Floods are dreaded and leave 

 much destruction in their wake, and yet the productive 

 river bottoms owe their fertility to the mineral sub- 

 stances brought in solution and the new layers of soil 

 left by the flood. 



Permission United States Geological Survey. 

 FIG. 44. View of Delaware water gap, a productive river valley. 



Hard and soft water. The terms hard and soft water 

 are in common use in the home. You know, too, that 

 hard water lathers soap only with difficulty, while soft 

 water lathers it freely. On this basis we can classify 

 rain water as soft water, while water from the spring or 

 well is hard. Since all spring and well water were once 

 rain water, it is evident that they have become hard in 

 passing through the earth. The hardness is due to the 

 mineral substances held in solution by the water. Some- 

 times hard water becomes soft after boiling. The minerals 

 held in solution are deposited on the bottom of the vessel, 



