GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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50 <strong>GROUND</strong> <strong>WATER</strong> <strong>IN</strong> <strong>NORTH</strong>-<strong>CENTRAL</strong> <strong>TENNESSEE</strong><br />
50 to 250 feet of limestone. The Cannon fauna is of late Middle<br />
Ordovician (Trenton) age, though it is not within the scope of this<br />
project to reelassify the fossil species according to Ulrieh's restricted<br />
definition.<br />
The Cannon limestone crops out beneath the Catheys in areas of<br />
medium altitude on the east flank of the Nashville dome. It is<br />
generally absent on the west flank of the dome, though at some places<br />
its truncated and overlapping edge comes between the Catheys and<br />
Bigby limestones. It is not known to exist in the Wells Creek Basin<br />
of Stewart County.<br />
BIGBY LIMESTONE<br />
The Catheys limestone, or the Cannon limestone where that forma<br />
tion is present, is underlain at most places on the north and west sides<br />
of the Nashville dome by the Bigby limestone, the type locality of<br />
which is the basin of Bigby Creek, a tributary of the Duck Kiver in<br />
western Maury County. At and near its type locality the Bigby<br />
limestone comprises relatively homogeneous beds of semi-oolitic or<br />
granular crystalline phosphatic gray or bluish limestone. Beds of<br />
sandy calcareous shale several feet thick occur locally at the top of<br />
the formation, and shaly beds occur locally at its base. The formation<br />
ranges in thickness from 30 to 100 feet, but the minimum thickness<br />
as deposited was about 50 feet. In the upper part of the forma<br />
tion in this region bryozoans are very abundant, especially Constel-<br />
laria teres, C. florida emaciata, C. grandis, and Eridotrypa briareus.<br />
Other fossils are found only in local thin shaly layers or in small<br />
lenticular beds of pure limestone. The lower fourth of the formation<br />
is almost devoid of fossils except Rafinesguina alternata and the<br />
minute forms of Mollusca which are common to all the phosphatic<br />
limestones of central Tennessee.<br />
As the formation is traced northeastward to and beyond Nashville<br />
it is found to thicken materially and become less granular and more<br />
fossiliferous. At Nashville it is separated from the overlying Catheys<br />
formation by a minor disconformity and is divisible into three dis<br />
tinct members, which are well exposed in an abandoned quarry south<br />
of the Tennessee Central Kailroad at Loveman's crossing, in east<br />
ern Nashville. (See pi. 7, A) The topmost member, which is gener<br />
ally about 28 feet thick, is a dark-blue medium-grained limestone,<br />
which contains a few large colonies of Stromatocerium pustvtosum;<br />
this is the Ward limestone of Safford. 4 The member is underlain by<br />
8 to 12 feet of very compact, brittle, heavy-bedded limestone which<br />
is dove-colored on fresh surfaces but chalky white on weathered<br />
surfaces; this is the " Dove " limestone of Safford. The basal member<br />
at Nashville is the "Capitol" limestone of Safford, about 25 feet<br />
* Safford, J. M., The geology of Tennessee, pp. 277-278, 1869. Jones, P. M.f Geology of Nashville and<br />
vicinity [thesis, Vanderbilt University], 56 pp., map, Nashville, 1892.