SOILS: THEIR PROPERTIES 

 AND MANAGEMENT 



CHAPTER I 



SOME GENERAL CONSIDERATIONS 



The broken and weathered fragments of rock that 

 cover in a thin layer the solid part of the earth and that 

 furnish the foothold and, in part, the sustenance for plant 

 life, are termed soil. Soil comes from rock and returns 

 to rock. It is merely a transitory stage in the change 

 from one form of rock to another. It is never still. From 

 the time when the particle leaves the disintegrating rock 

 until it is again cemented in the skeleton of the earth, 

 it is subjected to almost constant movement and to the 

 action of numerous forces that change it chemically and 

 physically. It is the movement, the strain and the 

 stress, the hard treatment at the hands of disintegrating 

 agencies, that make the soil useful to plant life. 



It was only the simpler forms of plants, however, that 

 first throve on the pulverized rock. Tribe after tribe of 

 plants has invaded the soil. Each has wrested from it 

 the mineral matter necessary for its growth and develop- 

 ment. Each has, in the end, left not only the mineral 

 matter that it obtained from the disintegrated rock, but 

 also the carbon and the oxygen that had been won from the 



