GROUND WATER IN NORTH-CENTRAL TENNESSEE

124 GROUND WATER IN NORTH-CENTRAL TENNESSEE
In general, the ground water associated with the Chattanooga
shale near its outcrop is "black sulphur" water, iron being taken into
solution as the sulphate from oxidized portions of the pyritiferous
shale and the sulphate being reduced by the carbonaceous matter of
the shale. Generally the water contains less than 500 parts per
million of dissolved mineral matter and the hydrogen sulphide is less
than 10 parts per million. The water associated with the crystalline
Silurian limestones has the least average content of dissolved solids,
is relatively soft, and has little noncarbonate hardness; hence it is
suitable for many uses without any preliminary treatment. The
water that issues from the Bigby limestone generally contains more
matter in solution and appreciably more sodium and potassium than
the water carried at similar depth by other stratigraphic units of the
same water-yielding capacity. At several localities, especially in the
vicinity of Nashville, the dense limestone beds of the Cannon and
Bigby limestones contain blebs of petroliferous material, and some of
the associated ground water contains sufficient oil in the emulsified
state to impart a disagreeable taste and a pronounced opalescence.
Other than these general relations, however, little correlation can be
made between chemical character of the ground water and the strati-
graphic horizon of the water-bearing bed.
SUMMARY DESCRIPTIONS BY COUNTIES
CHEATBAM COUNTY
[Area, 314 square miles. Population, 9,025 ]
GENERAL FEATURES
Cheatham County lies in the geographic center of the area covered
by this report and is bounded on the north by Montgomery and Rob-
ertson Counties, on the east by Davidson County, on the south by
Williamson County, and on the west by Dickson County. The area
is wholly rural. The county seat and largest community, Ashland
City (population, 712) is situated in the valley of the Cumberland
River on the Tennessee Central Railroad.
Cheatham County includes the stream gaps by which the Nashville
Basin drains northwestward across the Highland Rim Plateau (see pp.
16-18) and hence has a rather rugged topography. From the Cum­
berland River northward the surface is a dissected plateau comprising
flat and gently rolling interstream tracts whose altitude ranges from
700 to 780 feet above sea level and closely spaced subparallel youthful
drains adjusted to the Cumberland River at 350 feet above sea level.
Sink-hole topography exists locally on these interstream plateau
tracts but is not characteristic of them within Cheatham County.
The topography of the central and southern parts of the county,
'» Figures for population from 1930 census.