22 THE PRINCIPLES OP AGRICULTURE 



in doing so, aid in the formation of plant -foods. 

 The soil, therefore, is not merely an inert mass, 

 operated upon only by physical and chemical 

 forces, but it is a realm of intense life ; and the 

 discovery of this fact has radically modified our 

 conception of the soil and the means of treating 

 it. Enriching the land is no longer the adding 

 of mere plant -food : it is also making the soil 

 congenial to the multiplication and well-being 

 of micro-organisms. 



2c. Transportation of soils 



36. The soil is never at rest. The particles 

 move upon each other, through the action of 

 water, heat and cold, and other agencies. The 

 particles, whether of inorganic or organic origin, 

 are also ever changing in shape and composition. 

 They wear away and crumble under the action 

 of weather, water, organic acids of the humus, 

 and the roots of plants. No particle of soil is 

 now in its original place. These changes are 

 most rapid in tilled lands, because the soil is 

 more exposed to weather through the tillage 

 and the aerating effect of deep-rooted plants 

 (as clover) ; and the stirring or tilling itself 

 wears the soil particles. Even stones and pebbles 

 wear away (26a) ; and the materials which they 

 lose usually become productive elements of the 



