80 SOILS: PROPERTIES AND MANAGEMENT 



and character of the weathering and the constitution of 

 the parent minerals. 



24. Practical relationships of weathering. — Weather- 

 ing processes result in a general simplification of com- 

 pounds. Their action first affects the rock, with the 

 result that a soil is produced ; but they still remain ac- 

 tive in the soil after it is in a condition to support plants. 

 The physical agencies especially tend to loosen and fine 

 the soil, contributing largely to its tilth. The farmer 

 encourages such influences by plowing his land and by 

 other operations. Were it not for such weathering 

 action, the soil would become physically unable to afford 

 foothold for plants. The continued chemical changes 

 resulting in solution and carbonation provide a soil water 

 rich in plant-food nutriment. Weathering, then, by a 

 slow process over geologic periods has provided us with 

 soil, and by the same slow process is maintaining the 

 fertility of this creation. The encouragement and control 

 of such an agency is of no small importance in agricultural 

 practice. 



