lenticular, and may be up to 3 m (10 ft) thick, but extend laterally only a 

 few hundred feet. These deposits usually grade laterally into sand or clayey 

 sand. The upper surfaces of the deposits may be eroded, resulting in 

 irregular, discontinuous beds. These kaolinitic deposits are less plastic 

 than other clays and are used to control shrinkage in bricks and ceramics. 

 Older deposits of clay, of Miocene age, are found in northern Mobile and 

 Baldwin Counties, as well as along the major streams in Mobile County. Much 

 of the clay is difficult to locate, as it is concealed beneath a thick soil 

 layer and vegetation (Moser and Chermock 1978). 



The quantity of sand, gravel, and clay mined in Mobile and Baldwin 

 Counties has increased over the past decade, although production figures vary 

 considerably from year to year. Production of these minerals in the study 

 area increased sevenfold between 1971 and 1979, from 208,610 metric tons 

 (230,000 short tons) to 1,541,900 metric tons (1,700,000 short tons). This 

 comprises about 14% of the total production from the State of Alabama (Friend 

 et al . 1981). 



The 1973 Minerals Yearbook (Corey 1976) quotes production of 1,474,000 

 metric tons (1,624,000 short tons) of clay in Alabama in 1972, which 

 increased \1% to 2,630,000 metric tons (2,900,000 short tons) in 1973. The 

 1973 Atlas of Alabama (Lineback 1973) states the value of the annual 

 production of clay statewide is $7,000,000, which corresponds well with Smith 

 and Gilbert's (1975) figure of $8,000,000 in 1975. Table 24 summarizes the 

 production of clays in coastal Alabama for 1977 and 1979. 



Smith and Gilbert (1975) list the annual production of fire clay state- 

 wide at 363,000 metric tons (400,000 short tons) and that of common clay and 

 kaolin at over 1,816,000 metric tons (2,000,000 short tons), although Beg 

 (1980) lists the statewide annual production of clays other than bentonite 

 ("other clays" and "kaolin") at only 1,541,300 metric tons (1,697,841 short 

 tons). Table 25 summarizes the production of clays, excluding bentonite, in 

 Alabama for 1975, 1977, and 1979. 



Beg (1980) lists production of 103,500 metric tons (114,000 short tons) 

 of bentonite statewide, whereas Smith and Gilbert (1975) quote 163,400 metric 

 tons (180,000 short tons) in Lowndes County alone. It is not clear whether 

 these data reflect a real decrease in clay production from 1975 to 1980 or 

 merely a difference in method of data collection. Table 26 shows the rela- 

 tive importance of Alabama clay reserves to the nation as a whole. 



SAND AND GRAVEL 



Sand grains are formed by weathering action upon parent rocks, particular- 

 ly siliceous or other hard rocks, such as mica, magnetite, or cassiterite. 

 Most sand particles are quartz. The particles are rounded by abrasion and 

 sorted by the actions of wind and water. In water the larger, heavier 

 particles settle out first, with the smaller, lighter particles remaining in 

 suspension longer and being distributed over wider areas. These suspended 

 particles are carried downstream, where they may settle along sand bars. The 

 average depositional grain size is a function of the local current regime. 

 Eventually the sand may be covered by other sediments, or it may be trans- 



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