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bonate originally present has been replaced by a secondary accretion of crystal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