Table 4-3. Minerals Occurring in Beach Sand 



* These are light minerals with specific gravity not exceeding 2.87. The remaining 

 minerals are heavy minerals with specific gravity greater than 2.87. Heavy minerals 

 make up less than 1 percent of most beach sands. 



4.23 COHESIVE MATERIALS 



The amount of fine-grained, cohesive materials, such as clay, silt, 

 and peat, in the littoral zone depends on the wave climate, contributions 

 of fine sediment from rivers and other sources, and recent geologic his- 

 tory. Fine-grain size material is common in the littoral zone wherever 

 the annual mean breaker height is below about 1.0 foot. Fine material is 

 found at or near the surface along the coasts of Georgia, western Florida 

 between Tampa and Cape San Bias, and in large bays such as Chesapeake Bay 

 and Long Island Sound. These are all areas of low mean breaker height. 

 In contrast, fine sediment is seldom found along the Pacific coast of 

 California, Oregon, and Washington, where annual mean breaker height 

 usually exceeds 2.5 feet. 



Where rivers bring large quantities of sediment to the sea, the 

 amount of fine material remaining along the coast depends on the balance 

 between wave action acting to erode the fines and river deposition act- 

 ing to replenish the fines. (Wright and Coleman, 1972.) The effect of 

 the Mississippi River delta deposits on the coast of Louisiana is a pri- 

 mary example. 



Along eroding, low-lying coasts, the sea moves inland over areas 

 formerly protected by beaches, so that the present shoreline often lies 

 where tidal flats, lagoons and marshes used to be. The littoral materials 

 on such coasts may include silt, clay and organic material at shallow 

 depths. As the active sand beach is pushed back, these former tidal flats 



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