GROUND WATER IN NORTH-CENTRAL TENNESSEE

STRATIGRAPHY 37
has been completely leached, so that the layers of chert are separated
only by seams of yellowish clay a few inches thick. The beds of
earthy limestone weather to masses of soft shaly clay.
In general the beds of the Fort Payne formation are not highly
soluble, so that large solution channels are less extensively developed
and tubular springs are less abundant in this formation than in the>
overlying St. Louis limestone. Locally, however, these springs are a,
reliable source of water. In many places the dense tabular cherts-
have been minutely fractured by weathering, so that they yield water
rather freely to springs and to drilled wells, although drilling in such*
material is extremely difficult. The calcareous sandstone members
in the upper part of the formation supply many perennial springs from
their weathered and leached outcrops along the Highland Rim escarp­
ment in Williamson County and adjacent areas. (See pp. 210-211.)
However, their water-yielding capacity where they lie beneath cover
and are unweathered is not known, except that the earthy limestone
facies of the formation has no promise as a source of water.
NEW PROVIDENCE SHALE
The Fort Payne formation is underlain locally by the New Provi­
dence shale, the type section of which in Tennessee occurs at Whites
Creek Spring, 12 miles north of Nashville, as described by Bassler.56
At this locality the New Providence shale is 35 feet thick and consists
of coarsely crystalline white to gray crinoidal limestone in layers 12 to
18 inches thick, which are separated by thin bands of green and blue
shale. At many places the rock is but an assemblage of crinoid frag­
ments and other fossils loosely cemented by greenish shale, which is
entirely decomposed by weathering so that the fossils are freed in
great abundance. Toward the southwest, west, and east the forma­
tion thins notably and pinches out within a distance of 5 to 10 miles.
The New Providence shale also occurs in eastern Sumner County,,
where, according to Mather, 67 it comprises variable beds of shale and
shaly limestone that have a predominant bluish-green tint and inclose
many geodes. However, chert is not a common constituent. At
most localities the more calcareous strata are less than 10 inches thick,,
but in places they are very massive. Cross-bedding occurs at many
localities and is locally developed to a remarkable degree, the diver­
gence between the false and the true bedding being as much as 10°.
In this area the New Providence shale attains a maximum, thickness
of 55 feet along the Highland Rim escarpment north of Bransford and
Bethpage but thins toward the northeast.
In the Whites Creek Springs section the most abundant and charac­
teristic fossils are the bryozoan Bhombopora incrassata Ulrich and the
M Bassler, B. S., The Waverlyan period of Tennessee: U, S. Nat. Mus. Proc., vol. 41, pp. 218-220,1911.
w Mather, K. F., op. cit., pp. 21-23.