18 FIRST PRINCIPLES OF AGRICULTURE. 



CHAPTER H. 

 Origin and Formation of Soils. 



Soils : Their Origin, Formation, and Classification. 

 Every growing thing can be traced back to two primary 

 sources, the atmosphere and the soil. Every chemical 

 element contained in plants or in animals produced from 

 plants can be found either in the soil or atmosphere. 



The constituents which plants derive from the atmos- 

 phere are so abundant everywhere that the continuous 

 growth of maximum crops cannot exhaust them, and no 

 particular efforts are required to increase their efficiency 

 to the plant. The constituents of the soil are much less 

 abundant, and the power of the plant to secure them 

 depends very largely upon the effort of the farmer. To 

 the farmer, then, the soil is the object of first attention. 



"What is a Soil ? The soil is the name given to that 

 part of the earth that can be cultivated, and in which 

 plants can grow. 



Origin of Soils. Soils are derived, directly or in- 

 directly, from the rotting or decay of rocks. If all the 

 earthy matter which composes soils could be removed 

 from the surface of the earth, the remainder would be 

 solid rock. Rocks have been formed by the action of 

 fire and water ; hence they are classed as " igneous," that 

 is, produced by the action of fire, or " aqueous," produced 



