GROUND WATER IN NORTH-CENTRAL TENNESSEE

DICKBON COUNTY 141
the Highland Rim plateau in the vicinity of Tennessee City. The
massive suberystalline limestones of the St. Louis limestone and
Warsaw formation underlie the surface throughout the western half
of the county and cap the interstream tracts as far eastward as the
county boundary. These rocks do not appear at the surface on any
of the remnants of the Highland Rim plateau, however, being covered
by a mantle of cherty residual clay soil as much as 80 feet thick. The
thin-bedded earthy and cherty limestone of the Fort Payne formation,
which underlies the Warsaw formation, forms the lower slopes of the
valleys throughout the eastern half of the county. The underlying
Chattanooga shale is known to crop out in only two small areas near
the eastern boundary of the county, one in the bed of Jones Creek
Valley about 4 miles above its mouth and the other in Turnbull Creek
Valley between Beaverdam and Nails Creeks. The lithology and
stratigraphy of these rocks has been discussed on pages 31-41; their
distribution is shown on Plate 4.
GROUND-WATER CONDITIONS
As is generally true in an area underlain by limestone, the ground-
water conditions in Dickson County vary considerably from place to
place and for the most part are not related to the stratigraphy.
Rather, the ability of a stratum to transmit water is dependent upon
the number and size of solution channels and hence is indirectly
dependent upon the solubility of the limestone, the number and per­
sistence of joints, and the position of the stratum with respect to past
and present equilibrium profiles of solution channeling. If, as in
Dickson County, the strata do not differ materially in solubility, the
water-bearing properties of the rocks are determined by factors that
are largely independent of stratigraphy and are relatively constant for
a given physiographic district. (See pp. 78-82.)
Dug and drilled wells in the residual cl-ay that overlies the limestone
on the Highland Rim plateau generally obtain sufficient water for the
needs of a single household from coarse chert debris, especially just
above the underlying rock. In some places, however, the residual
material is not water bearing or its permeability is so slight that the
wells are inadequate during long dry periods. The depth of wells hi
this material ranges from 25 to 80 feet or more. Drilled wells that
pass through the residual soil find water in channeled zones either in
the uppermost part of the limestone or at greater depth. Such wells
are generally less than 200 feet deep. Many of the dwellings on these
plateau tracts derive their water from rain catches and cisterns.
In the mature and youthful terrane at lower altitudes than the
Highland Rim plateau channeled zones in the limestone are not likely
to be persistent at any one level or depth below the surface; hence
ground-water conditions are exceedingly erratic, and drilling for water