GROUND WATER IN NORTH-CENTRAL TENNESSEE

36 GROUND WATER IN NORTH-CENTRAL TENNESSEE
part of the formation consists of beds of somewhat earthy blue lime­
stone between 2 and 18 inches thick, which are accompanied by quartz
geodes from 1 to 12 inches in diameter and by nodular and irregular
tabular masses of chert. The amount of chert decreases noticeably
and the proportion of earthy limestone and calcareous shale increases
from the top of the formation toward the bottom. In the south-
central and southwestern parts of the region, especially in Williamson,
Dickson, and Humphreys Counties, the upper part of the formation
includes many beds of coarse sandy limestone or calcareous sandstone,
whose weathered and leached outcrops resemble buff sandstone.
Locally, in the same district, the lower part of the formation, according
to Safford,52 is a massive blue-gray limestone whose maximum thick­
ness is 150 feet. According to Mather & the upper 50 to 60 feet of the
formation in the northeastern part of the region, in Simmer County,
consists of thin-bedded buff or brownish-gray limestone that contains
numerous geodes and much tabular chert. This upper division is
underlain by about 30 feet of relatively pure coarsely crystalline lime­
stone hi massive beds, which inclose tabular masses of light-brown or
milky-white chert from 3 to 12 inches thick that become less abun­
dant in the lower beds of the division. Estimates by several geologists
of the thickness of the Fort Payne formation range from 90 to 275 feet,
although the stratigraphic limits of the sections covered by these
estimates, especially the lower limit, may not be strictly equivalent.
The Fort Payne formation is essentially nonfossiliferous in north-
central Tennessee, although locally, as in western Overton County,64
the upper 20 feet contains many fragments of crinoids, the presence of
which differentiates these beds from the overlying Warsaw formation.
However, fossils are comparatively abundant in the Fort Payne of
other areas and also in beds that underlie the Fort Payne. The for­
mation is now classified by Butts,55 who has studied the formation over
a broad region in Kentucky, Tennessee, and Alabama, as containing
beds of Keokuk, Burlington, Fern Glen, and late Kinderhook age.
The Fort Payne formation forms the Highland Rim plateau in
eastern Sumner County and crops out extensively over the middle and
lower slopes of the dissected part of the plateau along the Highland
Rim escarpment and in the valleys of the Tennessee and Cumberland
Rivers. The formation is deeply weathered throughout the upland
areas, and the weathering has generally produced a reddish or
yellowish-buff soil that contains much dense chert in subangular
fragments. In many places the tabular chert has not disintegrated,
although the calcareous matter of the intervening limestone layers
« Safford, J. M., Geology of Tennessee, p. 340,1869.
» Mather, K. F., op. cit., p. 24.
s* Butts, Charles, op. cit., p. 15.
« Butts, Charles, Geology of Alabama: Alabama Geol. Survey Special Kept. 14, pp. 166-167,1926.