WORK OF GROUND-WATER 



35 



c(|u;il or even exceed the amount consumed in the hydration of 

 minerals. 



WORK OF GROUND-WATER 



Ground-water works chemically and mechanically, the chemical 

 work being the more important. 



Chemical work. The chemical and chemico-physical action of 

 ground-water may be grouped in several more or less distinct 

 categories. 



i. The simplest result is the solution of mineral matter. Pure 

 water dissolves little mineral matter; but the carbon dioxide ex- 

 tracted from the atmosphere, and the products of organic decay 

 extracted from the soil, give the water added power to dissolve. 

 The solvent work of ground-water is shown by the fact that all 



V\K. 22. Sections of petrified logs, near Holbrook, Ariz. Age probably 

 Jurassic. 



water from springs and wells contains mineral matter, while rain 

 water is essentially free from it. The subtraction of soluble matter 

 from rock tends to make it porous, and helps it to decay. 



2. One mineral substance in solution may be substituted for 



