GROUND WATER IN NORTH-CENTRAL TENNESSEE

178 GROUND WATER IN NORTH-CENTBAL TENNESSEE
ward, the Catheys, Cannon, and Bigby limestones, the Hermitage
formation, and the Lowville limestone, including the Carters member.
The Upper and Middle Ordovician formations crop out only as narrow
bands on the upper and middle slopes of the hilly country along the
boundaries of the county. The Hermitage formation comprises
earthy limestone, calcareous shale, and calcareous sandstone associ­
ated with thin-bedded limestone; the other formations are composed
wholly of limestone. The Middle Ordovician strata are underlain
successively by the Lebanon, Ridley, Pierce, and Murfreesboro lime­
stones, of Lower Ordovician age. The thin-bedded Lebanon lime­
stone usually underlies the lower part of the hill slopes along the
boundaries of the county but also crops out over extensive tracts along
the edges of the central peneplain, especially in the southern half of
the county. The dense massive beds of the underlying Ridley lime­
stone are the surface rocks over the greater part of the central pene­
plain, the outcrop area of this formation being slightly more than half
the area of the county. The Pierce and Murfreesboro limestones
crop out in several relatively small areas on the apexes of minor
structural domes within 9 miles of Murfreesboro. These two forma­
tions are the oldest rocks that crop out in the Nashville Basin and are
not known to be exposed anywhere in central Tennessee outside of
Rutherford County. The lithologic character and stratigraphic
relations of these rocks are discussed on pages 35-38; their areal dis­
tribution is shown on Plate 4. The nature of the rocks that lie
beneath the Murfreesboro limestone and do not crop out within the
county are shown by the record of the Franklin Oil & Fuel Co.'s well
(No. 427, pi. 4 and pp. 60-61).
GROUND-WATER CONDITIONS
The rocks that underlie the Nashville Basin peneplain in the central
part of the county, being all limestones, are not generally permeable
and carry water only in solution channels, bedding planes, or joints
(pp. 69-89). Hence the water-bearing properties of any one stratum
may differ greatly from place to place, as the number and size of
solution channels are dependent chiefly upon the solubility of the
rock, the number and continuity of joints, and the position of the
stratum with respect to present and past equilibrium profiles of
erosion. In general water-bearing openings are much fewer in the
massive, thick-bedded rocks such as the Ridley and Murfreesboro
limestones than in the thin-bedded and less competent rocks such as
the Hermitage formation and the Lebanon and Pierce limestones.
However, some of the largest solution conduits of the district occur in
the more massive facies of the limestones. So far as is known, there
are no water-bearing channels related to the unconformities nor any
bodies of limestone that have been depressed with relation to the