GROUND WATER IN NORTH-CENTRAL TENNESSEE

STRATIGRAPHY 43
Specimens from the type locality [of the Jeffersonville limestone] at the Falls of
the Ohio show in an insoluble residue from fresh material the presence of about
1 per cent silica in the form of small biterminal quartz crystals. There is appar­
ently a complete absence of transported sand grains.
Fresh specimens of the massive limestone from the lower portion of the Pegram
limestone (Jeffersonville) in the vicinity of Pegram, Cheatham County, Tenn.,
retain in their insoluble residues from 15 to 20 per cent sand grains of minute size,
most of which are more or less completely frosted. The distance they have been
transported is apparently considerable.
In outliers near and on the Highland Rim plateau north of Hartsville, Trous-
dale County, Tenn., are present outcrops of a varying thickness of the Jefferson­
ville formation. The almost exclusive constituent is here a coarse biterminally
crystalline quartz sand which has undergone no abrading. The occurrence of
much of the sand would suggest a diagenetic origin in which the calcium car­
bonate originally present has been replaced by a secondary accretion of crystal­
line quartz about the original sand grains.
I suspect that the sandstone has a considerable subsurface distribution, for
the extent of its areal distribution is indicated in the presence of the identical
sandstone in the western portion of Davidson County, 50 miles to the south­
west of its occurrence in Trousdale County.
Many test wells that have been drilled in search of oil in eastern
Dickson County (see pp. 142, 144-146) encounter ground water,
which is reported to issue from the Chattanooga shale. It is ex­
tremely doubtful, however, whether the typical shale is sufficiently
permeable to be water bearing, and hence the true source of the water
is likely to be in some permeable bed that lies just above or just
below the shale. It is possible that the source is the basal sandstone
member of the Pegram limestone, which may persist westward be­
neath cover. This possibility is somewhat enhanced by the fact
that in general the Devonian formations are more persistent toward
the west.
CAMDEN CHERT
At the "whirl" on the Buffalo River, in southern Humphreys
County, the Pegram limestone is underlain by 45 feet of alternating
layers, from 2 to 9 inches thick, of dense bluish-gray limestone and
yellowish chert. These strata are believed by Dunbar w to be tran­
sition beds between the Camden chert of Safford and Schuchert 81
and the overlying Pegram limestone, inasmuch as the fauna contains
both the very diagnostic Amphigenia curta, of Camden age, and later
species, such as Spirifer macrothyris. Strata which are very similar
to those at the "whirl" crop out 5 miles farther west at Hurricane
Rock Spring (No. 181, p. 161), on the Duck River, and are probably
also to be correlated with the Camden chert. The formation is not
known to occur elsewhere in north-central Tennessee.
M Dtinbar, 0. O., op. dt., pp. 80-81.
81 SafEord, J. M., and Schuchert, Charles, Tne Camden chert of Tennessee and its lower Oriskany fauna:
.Am. Jour. Sci., 4th ser., vol. 7, pp. 429-432,1899.