24 THE PRINCIPLES OF SOIL MANAGEMENT 



soluble. It is this solvent action of carbonated water 

 which has formed the extensive caverns and passages 

 in every fairly pure limestone formation, and thereby 

 has given rise to such features as the Mammoth Cave 

 and the great sinks of Southern Missouri, Kentucky, 

 Tennessee, Georgia, Florida and many other regions 

 underlain by limestone. 



In the superficial layers of soil, organic acids also 

 add to the solvent power of the water. 



Since water is an universal solvent, in the earth it 

 contains a large variety of mineral compounds, all of 

 which affect its solvent power, usually increasing it. 



The destructive action of solution is indicated by the 

 considerable amount of dissolved substances in all 

 natural waters. The Mississippi river carries in solution 

 annually sufficient material to cover a square mile of 

 land ninety feet deep; the Danube, sufficient material 

 for a depth of eighteen feet; and the Nile, sufficient 

 material for a depth of thirteen feet. 



(2) The mechanical action of water. The destructive 

 action of running water transcends all other agencies 

 of rock degradation in its extent. It has been the most 

 potent force in carving the earth's surface into its present 

 form. It is continually at work reducing elevations 

 and filling depressions. 



This destructive action is due largely to the power 

 of running water to carry material. This transported 

 material becomes the tool of the water in wearing away 

 its channel. 



The transporting power of water varies as the sixth 

 power of its velocity of flow. That is to say, if the 



