GROUND WATER IN NORTH-CENTRAL TENNESSEE

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