GROUND WATER IN NORTH-CENTRAL TENNESSEE

StJMNEB COUNTY 199
mately N. 70° E. The Nashville Basin, which lies south of the escarp­
ment, is a rolling terrane whose summits level tracts from 550 to 600
feet above the sea are remnants of the Nashville Basin peneplain
and whose drains are youthful to submature valleys adjusted to the
present stage of the Cumberland River, about 400 feet above sea level.
Numerous sink holes and undrained depressions occur along the south­
ern edge of the county in the meander belt of the Cumberland River.
The unconsolidated rocks of Sumner County include clay, sand,
and gravel deposited by the Cumberland River and its larger tribu­
taries during recent erosion cycles, also the mantle of residual clay
and chert fragments, at least 60 feet in maximum thickness, which
covers the bedrock of the Highland Rim peneplain.
Inasmuch as the county lies on the north flank of the Nashville
dome (pp. 62-63), its consolidated rocks constitute a monocline dip­
ping very slightly toward the north-northwest. Its geologic column
embraces strata that range in age from Mississippian to probably
Lower Ordovician. The youngest of these, the massive and some­
what cherty St. Louis limestone, constitutes the bedrock beneath the
Highland Rim plateau in the extreme northwestern part of the county,
although its visible exposures are limited to the steeper valley slopes.
This limestone is underlain successively by the Warsaw formation,
which comprises clay shale, calcareous shale, and thin beds of cherty
limestone near the top and bottom of its section, and by the Fort
Payne formation, which in this county consists of thin-bedded lime­
stone containing much nodular and tabular chert, with some sandy
beds. The Fort Payne formation is the bedrock of the Highland
Rim plateau in the northeastern quadrant of the county; it also
crops out in the deeper valleys farther west and on the uppermost
slopes of the Highland Rim escarpment. In the middle slopes of the
escarpment this formation is underlain in succession by the inter-
bedded limestone and calcareous shale that constitute the New Prov­
idence shale, by the carbonaceous Chattanooga shale, and possibly
by the Pegram limestone (Middle Devonian) or other rocks of De­
vonian age. The Chattanooga shale or the Middle or Lower
Devonian if present in Sumner County is underlain by Silurian
limestone, earthy limestone, and shale, which constitute a full sequence
from the Lobelville limestone down to and including the Brassfield
limestone. Of this sequence the Lobelville and Laurel limestones
both contain sandy beds that should be permeable to water. The
Brassfield limestone is underlain in turn by clay and shale and by
massive gray limestone, which may represent the Fernvale and Ara-
heim formations, respectively, of latest Upper Ordovician (Richmond)
age. These beds crop out along the base of the Highland Rim escarp­
ment. Farther south, on the Nashville Basin peneplain, the Arnheim
is underlain by limestones of Upper (?) and Middle Ordovician age, the