CHAPTER XIX 

 PHYSICAL STRUCTURE OF THE SOIL 



221. Kinds of soil. If we examine a handful of the soil from 

 near a lake shore, we may find it chiefly composed of sand. 

 Sometimes this sand is coarse or gritty and sometimes almost 

 as fine and smooth as flour. Near the water's edge quite coarse 

 sand may usually be found. Back from the lake, where plants 

 are growing abundantly, the sand is discolored and contains 

 the results of decay of plant and animal bodies. Where de- 

 cayed organic matter is abundant, the soil is called loam. In 

 some streams of water along the riffles small stones are found 

 in large numbers, and more or less sand is mixed with them. 

 This material is gravel, and a soil in which such material pre- 

 dominates is gravelly soil. Often by digging only a little way 

 down we find a soil which is composed of very fine and com- 

 pact material so compact that when moist it may be pressed 

 into balls which will hold together when thrown with great 

 force. This is clay. "Silt" is the name applied to the fine, rich 

 soil that is deposited by currents of water. It is commonly 

 deposited on broad bottom lands at times of high water. In 

 low, swampy ground, plants may grow in great quantity and 

 fall down year after year. Their bodies partially or completely 

 decay and become pressed into a porous soil known as peat. 

 It must be obvious that these different kinds of soils may be 

 found mixed together in various ways ; indeed, it is seldom 

 that any one of them is found unmixed with one or more 

 of the others. Thus we have sandy, clayey, or gravelly loam, 

 or a peaty soil in which a little clay, sand, and gravel are 

 mixed. There are many names for the various combinations 

 and grades of soils. 



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