KINDS OF SOIL 



IV.) 



on such soils. In humid regions the grains are rounded 

 from the rolling due to water movements. In arid regions 

 the grains are angular and of any sort of material, not 

 necessarily of silica. 



Fig. 42. — Sand soil. Organic matter applied to plat on the left. Soils 



Department, Wisconsin Station. 



2. Clay Soils. — Like the term sand, clay in soil nomen- 

 clature refers to size of particles, and is applied to soils, or 

 that portion of soils, having the very finest particles, regard- 

 less of composition. It has been truly said that clay is either 

 rock rot or rock flour. In the former case, and that is the 

 common occurrence, clay is derived from silicate rocks bv the 

 decomposing action of water and carbon dioxide. It is largely 

 hydrated aluminium silicate. In the latter case clay is 

 merelv verv finely ground rock material made by the action 

 of glaciers, for example, and the composition will depend 

 on the kind of rock ground up. 



3. Loam Soils. — The term loam does not mean much 

 scientifically, but popularly it is a term applied to soils of 

 good texture and well supplied with organic matter. They 

 are sand or clay loams as thev have more or less of the 

 qualifying constituent. Their chemical composition is very 

 general in nature. 



