GROUND WATER IN NORTH-CENTRAL TENNESSEE

WILSON COUNTY 221
entire Middle and Lower Devonian and the Silurian are absent
throughout the county, being cut out by overlap upon the Ordovi-
cian and by the major disconformity that marks the base of the
Chattanooga shale. The Fort Payne formation and the Chatta­
nooga shale cap the highest hills and ridges in the vicinity of Green-
vale, Statesvifle, and Watertown, in the southeastern quadrant of
the county, as is shown by Plate 4, but do not crop out elsewhere.
In a few places the Chattanooga shale is underlain by the nodular
earthy limestone and shale that constitute the Leipers and Catheys
formations, but in many others the Leipers and Catheys are missing
and the Chattanooga rests directly upon the Cannon limestone.
This formation, which comprises gray and blue argillaceous cherty
limestone at the top and massive dove-colored limestone in its lower
part, crops out extensively on the middle slopes of the hilly areas
and on some of the peneplain remnants farther north and west. The
Hermitage formation, which underlies it and comprises thin-bedded
argillaceous limestone, clay shale, and phosphatic shale, crops out on
the middle and lower slopes of the hills in the southeastern part of
the county and is widespread on the peneplain tract to the north and
west. Beneath the Hermitage are compact massive and thin-bedded
dove-colored cherty limestones, which constitute the Lowville, Leb­
anon, and Ridley limestones in succession from the top downward.
The Lowville limestone crops out on the lower slopes of some of the
hills and on the valley floors in the southeastern quadrant of the
county and on much of the higher ground farther west; the Lebanon
and Ridley limestones are the most widespread formations on the
dissected plain of the southwestern quadrant. So far as is known,
the lowest beds of the Ridley limestone and all underyling strata are
not exposed at any place within the county.
GROUND-WATER CONDITIONS
In Wilson County, as in other parts of the Nashville Basin, the
amount and chemical character of the ground water differ widely
from place to place. Most of the ground water is of meteoric origin
and circulates along joints, bedding planes, or other solution channels
of the limestone, the permeability of the rocks depending wholly
upon the frequency and size of these openings. In many places,
however, bodies of connate and other highly concentrated water are
trapped above or below impermeable shaly beds, in deeply buried
permeable strata, or perhaps in permeable zones related to uncon­
formities. In some of the interstream areas the channeled zones in
the limestone above the level of the streams have been drained, the
rocks below stream level are not water bearing, and domestic water
supplies must be derived from cisterns. Furthermore, at many
places on the peneplain remnants, bedrock is only a few feet below