54 SOILS AND FERTILIZERS 



the air. 20 This action results in adding vegetable 

 matter to the soil. 



56. Combined Action of the Various Agents. — In 



the decay of rocks the various agents named, — water 

 acting mechanically and chemically, heat and cold, 

 air, and vegetation, — have been acting jointly, and have 

 produced a more rapid disintegration than if each 

 agent were acting separately. One of the best evi- 

 dences that soil is derived from rock is that there are 

 frequently found in fields pieces of rock which are 

 actually rotten, and, when crushed, closely resemble 

 the prevailing soil of the field. This is particularly 

 true of clay soils where fragments of disintegrated 

 feldspar are found which, when crushed, resemble the 

 soil in which the feldspar was imbedded. 



DISTRIBUTION OF SOILS 



57. Sedentary and Transported Soils. — The place 

 where a soil is found is not necessarily the place wdiere 

 it was produced ; that is, a soil may be produced in 

 one locality and transported to another. Soils are 

 either sedentary or transported. Sedentary soils are 

 those which occupy the original position w T here they 

 were formed. They usually have but little depth be- 

 fore rock surface is reached. The stones in such soils 

 have sharp angles because they have not been ground 

 by transportation. Transported soils are those 

 which have been formed in one locality and carried by 



