GROUND WATER IN NORTH-CENTRAL TENNESSEE

CHEATHAM COUNTY 125
which are traversed by the Cumberland and Harpeth Rivers, is some­
what more diverse, the summit flats being less extensive and some of
the slopes along the major streams having submature profiles. The
youthful tributary drains in the southern part of the county are ad­
justed to the Harpeth River, which at Kingston Springs is about 440
feet above sea level.
The interstream flats of Cheatham County are underlain by 20 to
60 feet or more of cherty residual soil and clay resting upon the
massive subcrystalline beds of the St. Louis limestone and Warsaw
formation. The underlying Fort Payne formation, which in this
area consists of interbedded strata of dense bluish cherty limestone
and calcareous shale 1 to 3 feet thick, crops out on the slopes of the
tributary drains throughout the county. (See pi. 4.) The Chat­
tanooga shale crops out as a narrow band slightly above stream level
along the Cumberland River and some of its larger tributaries from
Ashland City eastward and intermittently along the Harpeth River
entirely across the county. Beneath this well-known horizon marker
limestones of Devonian and Silurian age crop out over the valley
floors. The Leipers formation, of Upper Ordovician age, and some
of the uppermost beds of the Middle Ordovician are exposed at stream
level along the Cumberland River eastward from a point near Ash­
land City. The general character and succession of these strata are
described on pages 33-53, and their areal extent is shown by Plate 4.
QROUND-WATER CONDITIONS
On the interstream plateau remnants most rural water supplies are
obtained from dug wells 25 to 50 feet deep, which tap the loose cherty .
debris or partly disintegrated limestone at or just above the contact
of the residual clay that rests on the St. Louis limestone. Many such
wells are inadequate for a single household during the summer in years
of subnormal rainfall. Hence each farmstead usually has a cistern
for storing rain water. Water for stock is generally impounded in
small pools by damming one or more ephemeral drains and conserving
storm run-off. The few drilled wells on these upland tracts obtain
water in channeled zones of the St. Louis limestone between 90 and
160 feet below the surface. To judge from the records of several deep
wells that have been drilled in Cheatham and adjoining counties in
search of oil, it does not seem likely that potable water will be found
by drilling to depths exceeding 200 feet in the upland tracts.
On the slopes of the youthful drains that dissect the Highland Rim
plateau many small tubular springs issue at several altitudes from
jointed and channeled limestone, and seepage springs from the cherty
residuum of the weathered rocks. Many rural dwellings are located
adjacent to perennial springs of this sort. Drilling for water on these
slopes is exceedingly uncertain, although successful wells from 35 to