THE SOIL 79 



distinguish them. These names are usually names of 

 towns near which the soils are first mapped. 1 



The local names used in any community are often 

 misleading. In a region where nearly all the soils are 

 sandy, a loam soil is usually called a clay; while, in regions 

 where most of the soils are heavy clays, the same loam 

 is likely to be called sandy. 



Soils are also named in many other ways. Glacial soils 

 are those that were formed as a result of glaciation, or the 

 passage of the great ice sheet that once covered part of 

 America. They occur in northern and eastern United 

 States. 



Arid soils are those that do not receive a sufficient 

 amount of rainfall to produce regular crops without irri- 

 gation. They occur in the western half of the United 

 States. Humid soils are those that receive sufficient 

 rainfall to produce crops. 



77. Importance of the Size of Soil Particles. The size 

 of the soil particles influences the water-holding power 

 of the soil, the amount of food that can be dissolved for 

 plant use, the ease of movement of air and water, the 

 growth of organisms in the soil, and the crop-producing 

 power. 



78. Relation of Size of Particles to Water. The rock 

 particles of the soil can hold water on their surfaces only, 

 hence the water-holding power of the soil increases when 

 the surface area of the particles is increased. 



Dip a pebble in water and a film of water will remain 

 on it when it is removed. Wipe the pebble and the water 

 will be gone, because no water has soaked into it. If such 



'Soil iimps arc based largely on the size of the particles, but origin, 

 topography, agricultural value, and other factors, are considered. 



