GROUND WATER IN NORTH-CENTRAL TENNESSEE

WJfetlAMSON
i&entf&nts, also in thfe middle of upper part of the hill slopes farther
feast. It rests unoonformably upon rocks that range in age from
lower middle Silurian to Middle Ordoviciah, the jpre-Chattanooga
Devonian rocks being absent in all parts of the county and the Silurian
and Upper Ordovician being absent east of Franklin. In a few
places particularly in the valleys of tributaries of Leipers Creek, a
branch of the Duck River, near fche soufchwesfc corner of fche county;
in fche valley of the South Harpeth River near thfc northern boundary
6f the county; also between the West Harpeth River and Murphy
Fork about 2% miles east-southeast of Hillsboro fche Chattanooga
shale rests upon the Osgood limestone or possibly Upon younger beds
of middle Silurian (Niagaran) age. In fche same localities the Chat­
tanooga shale, or the Osgood limestone where that formation is
present, is underlain in turn by the soft green or chocolate-colored
shale with associated bands of crystalline limestone and granular
crysfcalline limes fcone fchat constitute fche Fernvale and Arnheim forma­
tions, of Richmond age. The Leipers formation, which in fchis
county comprises knofcfcy earfchy limestone and shale or granular
crystalline limestone without shale, crops out at its proper strafci-
graphic horizon along fche base of fche Highland Rim escarpment,
also in the lower and middle slopes of Sugar Ridge and of the hilly
tract between Franklin and Brenfcwood. However, fche formation
thins eastward, both by unconformity at its top and by overlap at its
base, and is not known to crop out south and east of Franklin. The
Leipers formation, or the Chattanooga shale where the Leipers is absent,
rests upon knotty earfchy limestone and shale with associated thick beds
of impure limestone. These beds, which constitute the Catheys forma­
tion, do not crop out anywhere in the county west of the Highland
Rim escarpment. Together with the underlying massive Cannon
limestone and the granular, crystalline, laminated Bigby limestone,
the Catheys formation crops out on the lower slopes and aboufc fche
flanks of fche hilly tracts of the eastern half of the county. Sfcrati-
graphically beneath the Bigby limestone is the Hermitage formation,
which in the central part of the county comprises sandy, granular,
phosphatic limestone at the top and even-bedded shale and sandy
limestone below, but which along the east edge of the county is largely
thin-bedded sandy limes fcone. This formation crops out extensively
along the flanks of the ridge that divides the Harpeth and West
Harpeth Rivers in the central part of the county and on the middle
and upper slopes of the hilly areas in the eastern part of the county.
It is underlain successively by the massive compact cherty beds of the
Lowville limestone and by the thin-bedded compact Lebanon lime­
stone, of which fche most extensive outcrop covers the floor and lower
slopes of the Harpeth River Valley from the vicinity of Franklin
eastward to and beyond tbe boundary of the county. The Lowville