and sand; 0.5 to 0.002 mm. in diameter according to the 

 U. S. Department of Agriculture system, 0.02 to 0.002 mm. 

 in diameter according to the International system. (2) In a 

 general sense waterborne sediment in which the diameters 

 of individual grains are similar to those of silt (1). (3) Soil 

 material containing 80 per cent or more of silt (1) and less 

 than 12 per cent of clay. 



Silting (Siltation) 



The deposition of water-borne sediments in bodies of 

 water, caused usually by a decrease in the velocity of the 

 water movement. 



Silurian 



One of the geological periods in the Paleozoic era, which 

 began about 360 million years ago and lasted for about 35 

 million years. 



Silva 



The aggregate of the forest trees in an area or country. 



Silviculture 



The production and care of forest trees. 



Simian 



Refers to monkeys and apes, particularly anthropoid apes; 

 or used as a noun especially for the latter. 



Simoon 



An intensely hot, dry wind of Arabian and Saharan 

 deserts, usually carrying much sand. 



Sinkhole 



A hole into which water drains and passes into an under- 

 ground channel, occurring usually in limestone regions. 



Sinter 



Deposits, mainly siliceous and calcareous (Travertine), 

 formed in lakes or springs by evaporation, e.g., terraces of 



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