GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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STRATIGRAPHY 41<br />
and sulphate (SO4), probably derived from oxidation of the pyrite;<br />
generally it also carries a noticeable amount of hydrogen sulphide,<br />
although the quantity of this gas is usually less than 5 parts per mil<br />
lion. Many drilled wells obtain water supplies large enough for<br />
household use from the upper part of the shale close to its outcrop.<br />
In general the Chattanooga shale is not likely to be notably water<br />
bearing where it lies beneath deep cover and is unweathered, it being<br />
not unlikely that the ground water which is supposedly encountered<br />
in the shale in eastern Dickson County and elsewhere actually issues<br />
from sandstone of Devonian age.<br />
DEVONIAN SYSTEM<br />
Although a rather full sequence of Middle and Lower Devonian<br />
formations is exposed in the western valley of the Tennessee River,74<br />
rocks of the Devonian system are known at very few localities in<br />
north-central Tennessee. Those whose stratigraphy is well known<br />
are of Middle Devonian age, but Foerste 76 has identified Lower<br />
Devonian beds in the Wells Creek Basin of Stewart County. If the<br />
Chattanooga shale is wholly of Mississippian age, the Upper Devonian<br />
series is absent in north-central Tennessee.<br />
MIDDLE DEVONIAN SERIES<br />
PEGEAM LIMESTONE<br />
The type locality of the Pegram limestone is at Pegram, Cheatham<br />
County. The formation has been defined and its occurrence in<br />
central Tennessee described by Foerste.76 In the type section it is a<br />
relatively pure heavy-bedded light-gray limestone that attains a<br />
maximum thickness of 12 feet at its westernmost exposure in the<br />
quarry north of the Nashville, Chattanooga & St. Louis Railway at the<br />
bridge across the Harpeth River. Eastward from that locality the<br />
member thins, and 3 miles to the southeast, at Newsom, in south<br />
western Davidson County, it is only 3 feet thick. At Newsom the<br />
formation contains the diagnostic blastid Nucleocrinus verneuili, as<br />
well as Stropheodonta demissa, S. perplana, Rhipidometta penelope,<br />
and Nucleospira concinna. The only other known occurrence of the<br />
Pegram limestone in north-central Tennessee is at the whirl on the<br />
Buffalo River, which is 2K miles north of Bakerville, Humphreys<br />
County, and 46 miles west and somewhat south of the type locality.<br />
At that place the formation is a massive bed 3 feet thick, which is<br />
74 Dunbar, C. O., Stratigraphy and correlation of the Devonian of western Tennessee: Tennessee Geol.<br />
Survey Bull. 21,127 pp., 1019.<br />
75 Foerste, A. F., Silurian and Devonian limestones of western Tennessee: Jour. Geology, vol. 11, p. 682,<br />
1903.<br />
79 Foerste, A. F., Silurian and Devonian limestones of Tennessee and Kentucky: Geol. Soc. America<br />
Bull., vol. 12, pp. 425-426, 1901.<br />
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