ORIGIN OF SOILS 73 



brought down by rivers. It is estimated that the waste derived 

 from cliffs, etc., along the seashore is about three per cent, of that 

 brought down by rivers. 



Sands are deposited along the shores of the sea. Boulders, 

 pebbles, and coarse sand, are deposited in order near in shore, and 

 the finer sands farther out. Beach sand derived from rocks of 

 neighboring cliffs or brought down by torrential rains from 

 mountain regions is dark, and contains grains of many minerals 

 other than quartz. These sands contain more plant food and 

 make richer soils than sands from low-lying shores. The white 

 sand of low shore beaches, such as those on the east coast of the 

 United States from Virginia to Florida, consists almost entirely 

 of quartz grains. The other and softer minerals have been 

 entirely beaten to mud and deposited farther out during the long 

 period that the material has been exposed to the waves. These 

 sands are poor in plant food, but they are excellent soils for some 

 purposes. 



Sandstone consists of sand grains cemented together by silica, 

 carbonate of lime, or oxide of iron. Such deposits are widely 

 distributed, and many soils are derived from them. The quality 

 of the soil depends largely upon the origin of the sands. Quartz 

 is sandstone, which, by the action of heat and pressure, has been 

 metamorphosed in the crust of the earth. 



Muds are deposited beyond the sand deposits, and also in quiet 

 water near shore, and in river deltas. Muds contain the finer 

 particles from the wear of rocks. The soils derived from them 

 contain more plant food than sands and produce longer, but are 

 not adapted to the same kinds of plants. 



Muds may be consolidated into mudstone or shales or 

 metamorphosed by heat and pressure into schists and slates. Soils 

 are formed by the weathering of all these deposits. 



Limestone deposits are formed from the shells of molluscs, and 

 deposits of coral, and other marine organisms which secrete car- 

 bonate of lime from solution in the sea-water, some of which are 

 minute in size. These deposits are usually formed in the shallow 

 water beyond the area in which mud is deposited ; they also make 

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