GROUND WATER IN NORTH-CENTRAL TENNESSEE

52 GEOTJND WATBE IN NOETH-CBNTEAL TENNESSEE
(Orthis testudinarm of Safford), which is the most characteristic fossil
species of the formation. The lower portion of the formation, from
12 to 20 feet thick, is composed of thin-bedded earthy and sandy blue
limestone whose beds are separated by seams of gray or bluish shale.
At Nashville the formation retains these same general characteristics,
the subgranular upper beds with the characteristic Dalmanetta testu-
dinaria being well exposed in the quarry south of the Tennessee Cen­
tral Railroad at Loveman's crossing, in the eastern edge of the city,
although they are much thinner than in the Columbia quadrangle.
Toward the center of the Nashville Basin, in Williamson County and
western Rutherford County, the formation consists almost wholly of
flaggy beds of blue-gray sandy and earthy limestone separated by
seams of shale. These beds are usually devoid of fossils, are locally
phosphatic, and at many places simulate thin-bedded earthy yellowish
sandstone on weathered surfaces. Toward the northeast these flaggy
beds grade laterally into a highly variable series of impure limestone,
shale, and calcareous sandstone with local beds of cherty material.
The Hermitage formation ranges in thickness between 40 and 80 feet
in the Nashville Basin and crops out at its proper horizon throughout
the area. It is well exposed in the valley of the Harpeth River in the
vicinity of Franklin, where it is quarried at several points, and in the
valley of the Cumberland River about Nashville. In Rutherford
County and southern Wilson County it crops out only on the upper
slopes of the higher hills and ridges that surround the Nashville Basin.
In the Wells Creek Basin of Stewart County strata that are equivalent
to the Hermitage formation ("Saltillo limestone" of Foerste 9) crop
out beneath the Brassfield limestone, of basal Silurian (Albion) age,
although their .thickness and the nature of the contact are not dis­
closed. The Hermitage formation is of Middle Ordovician (basal
Trenton) age.
IOWVILLE LIMESTONE
In north-central Tennessee the Hermitage formation is underlain
disconformably by limestones that have heretofore been called Carters
limestone but are herein designated Lowville limestone, in accordance
with Bassler's assignment. 10 Beds of post-Lowville Black River age
are not known to occur in north-central Tennessee. Bassler has
divided this formation into an upper member, composed largely of
thin beds of very dense dove-colored limestone and yellowish-gray
shale, and a lower member, which comprises beds of compact white
or light-blue cherty limestone from 1 to 4 feet thick. The upper
member, which contains the guide fossil Tetradium cellulosum and
such other forms as Columnaria halli, Streptelasma profundum, and
Foerste, A. F., Silurian and Devonian limestones of western Tennessee: Jour. Geology, vol. 11, p. 690,
1903.
w Bassler, B. S., The stratigraphy of the central basin of Tennessee: Tennessee Dept. Education
Div. Geology Bull. 38, p. 60,1932.