GROUND WATER IN NORTH-CENTRAL TENNESSEE

GEOLOGIC STRUCTUKE 63
through central Tennessee and Kentucky to Cincinnati, Ohio. At.
Cincinnati the axis of the geanticline splits, one branch trending north­
westward and passing near Logansport, Ind., and the other branch
trending slightly east of north and passing close to Lima, Ohio. Crus-
tal warping along this axis began as early as Middle Ordovician time
and has continued at intervals until comparatively recent geologic
time, for the Highland Rim peneplain was deformed about this axis
as late as the upper Oligocene (pp. 19-20). During much of the Pale­
ozoic era part or all of the axial portion of the arch was above sea
level intermittently. In several epochs formations characterized by
distinct faunas were deposited simultaneously on opposite sides of the
arch or sediments were not deposited along the axis. This condition
was especially prevalent during the Silurian :and Devonian periods.
In north-central Tennessee warping along the axis of this arch appar-.
ently began near the end of the Murfreesboro epoch, in Lower
Ordovician time, for Galloway 28 points out that near Lascassas, in
northeastern Kutherford County/the Murfreesboro limestone is folded
with reference to overlying strata. ;
SECONDARY FOLDS
Although the average dip of the strata in the Nashville dome is
generally less than 15 feet to the mile, so that the rocks appear hori­
zontal in small outcrops, secondary folds in which the rocks dip more
steeply occur at.many places on the flanks of the dome. These
secondary folds are generally less than 5 miles long and not more than
100 feet high.
Several secondary folds of this sort that occur on the highest part,
of the Nashville dome in Kutherford County have been described by
Galloway. 29 They are shown on Plate 4 by the outcrops of the Pierce
and Murfreesboro limestones, which are exposed only where the
apexes of the folds have been cut through by erosion. The largest
of the secondary anticlines of this group is an ovoid fold about 6 miles
long, 3 miles wide, and 80 feet high whose axis trends about N. 20° W.
through the eastern part of Murfreesboro. The complement of this
fold is a syncline from 1 to 3 miles wide and 40 to 80 feet deep which
adjoins it on the west and whose axis extends southeastward from
a point on the Stone River about 2 miles west of Murfreesboro to
Gum, a distance of about 9 miles. Just west of this syncline, in the
vicinity of the Barfield and Marshall Knobs, is the. largest secondary
dome within the county, a fold which is nearly 6 miles in diameter
and 100 feet high. The remaining secondary folds of Rutherford
County are considerably smaller. The Nashville pike crosses the
18 Galloway, J. J., Geology and natural resources of Rutherford County, Tenn.: Tennessee Geol. Survey
Bull. 22, pp. 62, 65, 1919.
* Idem, pp. 61-62.