ecological characterization atlas of coastal alabama - Data Center

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 too 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 cl ay i s di ffi c ul t to l ocate , as i t i s conceal ed beneath a thi c k soi l
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 17% 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 statewide
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, excl uding 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 relative
im portance of Alabama clay reserves to the nation as a whole .
SAND AND GRAVEL
Sand grains are formed by weathering action upon parent rocks, partic ularly
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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