4 FARM AND SCHOOL PROBLEMS. 



tive rocks the waters glided over the surface and increased the 

 volume of torrents and carried the debris of plants, soils and 

 rocks through the valleys to the borders of the oceans. These 

 are known as transported soils. 



As the earth grew older new forces came to assist in the 

 process of transformation of rocks to soils. The fragments of 

 rocks disengaged by heat, frost, plants and animals, were 

 attacked by the action of water and its solutions (carbon-dioxide 

 and oxygen) and were decomposed and transformed into gravel, 

 sand, silt and clay. 



To understand clearly the science of agriculture it is neces- 

 sary to become familiar with the meaning of the following terms : 



1. Land is the solid portion of the surface of the globe. 



2. Earth is the loose material covering most of the land. 



3. Soil is the earthly material capable of supporting plant life. 



4. Humus is partly decayed vegetable matter in the soil. 



*The inorganic constituents of the soil are but modified 

 particles of rock. They vary in size and are usually classified 

 according to size from the largest to the smallest as : rocks, 

 boulders, pebbles, coarse gravel, fine gravel, coarse sand, medium 

 sand, fine sand, very fine sand, silt, clay. 



Clay soils may have particles less than 1-25000 of an inch in 

 diameter. 



Loam is clay and sand mixed with rich decayed vegetable 

 matter. 



Peat is a soil composed almost purely of vegetable matter, 

 that is but slightly decomposed. 



Muck is soil composed of a large part of well decayed vege- 

 table matter. 



A study of the origin of soils shows that they have been 

 formed in various ways, and are known by different names : 



Sedentary or residual soils are those that remain directly over 

 the rocks from which they have been formed. 



Transported soils are those that have been carried by the 

 wind, water or glaciers. 



* Bulletin 24 of the U. S. Bureau of Soils gives a system of group- 

 ing and classification of soils according to size of particles. 



