GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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48 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
similar in its general aspects to and is actually a recurrence of the<br />
fauna from the underlying Catheys formation of Middle Ordovician<br />
(upper Trenton) age. Moreover, the Leipers and Catheys formations<br />
are very similar in lithology, so that extreme care must be used if<br />
they are to be discriminated accurately in the field.<br />
On the west side of the Nashville dome the Leipers formation<br />
reaches a maximum thickness of 100 feet but locally has been com<br />
pletely removed by erosion that began in Upper Ordovician (Lorraine)<br />
time. Toward the east, however, the formation thins and becomes<br />
less persistent, and over extensive areas on the east side of the basin<br />
it is entirely absent. These stratigraphic relations are due in small<br />
part to post-Leipers erosion but more especially to the fact that the<br />
Leipers formation overlaps or transgresses the flank of the Nashville<br />
dome from the west and was not deposited uniformly over the entire<br />
region. Northwest of the type area, however, in the Wells Creek<br />
Basin of Stewart County, the formation has not been found, although<br />
the stratigraphic relations have not been traced in detail, and it is<br />
not clear whether the omission is due to erosion or to overlap. At<br />
most localities the formation lies immediately beneath the Chatta<br />
nooga shale, although at some it is separated from the Chattanooga<br />
shale by Silurian and Devonian rocks.<br />
MIDDLE OKDOVTCIAN SERIES<br />
CATHEYS LIMESTONE<br />
On the north and west sides of the Nashville Basin the Leipers<br />
formation is underlain by the Catheys limestone, whose type area is<br />
the basin of Catheys Creek,98 a tributary of the Duck River in Lewis<br />
and Maury Counties. The two formations are separated by a slight<br />
erosional unconformity. The Catheys formation, as deposited, was<br />
not less than 50 feet and in some places was at least 100 feet thick,<br />
but the subsequent erosion removed much of the accumulated ma<br />
terial. The upper half of the formation is as a rule made up of com<br />
pact impure blue limestone in layers from a few inches to 4 feet thick,<br />
separated by thin layers of calcareous shale. Northward from the<br />
type locality more and more beds of fine-grained impure limestone<br />
appear in this part of the formation. The fossil fauna, which is re<br />
stricted to the fine-grained beds and with them increases in abundance<br />
toward the north, includes Brachiopoda, Mollusca, Crustacea, and,<br />
locally, Bryozoa. Several large ostracodes, of the genera Leperditia<br />
and Isochilina, are especially characteristic of these beds. The lower<br />
half of the formation is made up of highly variable beds of fossiliferous<br />
knotty and fine-grained earthy limestone and shale, many of which<br />
are identical in lithology with the overlying Leipers formation. In<br />
these beds Cyclonema varicosum is probably the most diagnostic fossil.<br />
" Hayes, O. W., and Ulricb, E. O., op. cit., p. 2.