GROUND WATER IN NORTH-CENTRAL TENNESSEE

GEOLOGIC STRUCTURE 65
nooga shale was not deposited across the apex of the dome, that the
lowest beds of the Fort Payne formation rest upon the Hardin sand­
stone member with a minor stratigraphic break intervening, and that
therefore folding about this axis began before Mississippian time.
He states further that folding was renewed at a later time, however,
for the Fort Payne formation and overlying bed® of Mississippian age
are deformed nearly as much as the Chattanooga shale.
In the vicinity of White Bluff, in the central-eastern part of Dick-
son County, the strata are arched into one or more anticlines. These
secondary folds have been disclosed by deep wells that penetrate the
Chattanooga shale (pp. 144-145), but they have not been mapped in
detail. They seem to be associated with a marked structural depres­
sion in northeastern Dickson County and northwestern Cheatham
County, in which the Chattanooga shale is 50 feet or more below sea
level as indicated by the records of several deep wells. Doubtless
other secondary folds will be found in the area north and west of the
Highland Rim escarpment and within the region covered by this
report when the stratigraphy is traced in detail.
Bassler 33 has pointed out that in many places in central Tennessee
sharp inclinations of the strata are due not to folding or warping of
the crust but to collapse and slumping of strata above caverns formed
by solution. On the Highland Rim plateau features of this sort
exist where solution caverns have formed in the Ordovician lime­
stone and the overlying Mississippian strata have collapsed, these
strata being in some places nearly vertical. Bassler points out fur­
ther that at some places in the Nashville Basin the topographic
slopes seem to conform to the rock strata, which may rise with the
slope of a hill and descend to its^base on the opposite slope, but that
such features may be due to slump above solution openings rather
than to original structure. Similar features are associated with the
unconformity at the base of the Chattanooga shale, for at several
places in the northern part of the Nashville Basin the Hardin sand­
stone member of the Chattanooga fills pre-Mississippian sink holes
30 to 40 feet deep, whereas in adjacent areas the member is less than
a foot thick. A similar feature was noted by Lusk 34 in the Flynn
Creek Basin, in the central part of Jackson County, where the Chat­
tanooga shale fills a preexisting sink hole 2 miles in diameter and as
much as 100 feet deep.
WELLS CREEK UPLIFT
In the vicinity of Cumberland City, in the southeastern part of
Stewart County, and the adjacent part of Houston County the strata
M Bassler, R. 8., Sink-hole structure in central Tennessee [abstract]: Washington Aead. Sci. Jour., Vol.
14, p. 374,1924.
* Lusk, R. Q., A pre-Chattanooga sink hole: Science, new ser., vol. 66, pp. 579-580,1927.