GROUND WATER IN NORTH-CENTRAL TENNESSEE

STJBFACE FEATURES OF CENTRAL TENNESSEE 21
A drainage system being established, dissection of the upland pro­
gressed. The resistant chert of the lower Mississippian was first
breached on the apex of the Nashville dome (see pp. 62-63), and tie
underlying soluble Silurian and Ordovician limestones were attacked
by streams planing laterally at the local profile of erosive equilibrium.
In this manner the Nashville Basin was formed, its bounding escarp­
ments being maintained by the resistance of the Mississippian rocks.
HIGH-TERBACE STAGE
Galloway 31 notes that waterworn chert and quartaate gravel caps
several hills at altitudes of 580 to 700 feet above sea level in the vicin­
ity of Lavergne, Walter Hill, and Lascassas, in northern Rutherford
County. He implies that these deposits, which are about 500 feet
below near-by portions of the Highland Rim plateau and 100 feet
above the floor of the Nashville Basin, indicate a stage of equilibrium
in the dissection of the Nashville dome. Lusk 32 describes alluvium-
veneered stream terraces at an altitude of about 700 feet in the valley
of the Cumberland River near Celina and Gainesboro, to the east of
the area covered by this report. Furthermore, flat-topped ridges
and terrace remnants at an altitude of 550 to 600 feet in the vicinity
of ClarksviUe seem to define a belt of stream planation several miles
wide which follows the lower course of the Cumberland Valley.
From this seeming terrace the surface rises by an old-age profile to
the Highland Rim plateau, at an altitude of about 700 feet, and de­
scends by precipitous youthful slopes to the present stream. Other
related features exist within the region, but in the absence of topo­
graphic maps it was impossible to discriminate them during the
course of the reconnaissance. These terrace remnants may well be
the product of general stream planation. The lithology of the post-
Vicksburg strata of the Gulf Coastal Plain does not seem to offer a
clue to a precise dating of this high-terrace stage. Galloway 33 has
expressed a belief that the cutting of the high terrace began in late
Pliocene time, although he gives no basis for his assignment.
PENEPIA1N STAGE
After the conclusion of the high-terrace stage the erosive power
of the streams was again quickened, and the soluble Ordovician lime­
stones in the apex of the Nashville dome were reduced locally by
lateral planation and solution to the profile of equilibrium of the
Cumberland River and its chief tributaries, the Harpeth and Stone
Rivers. Farther south the Duck River and the Elk River, tributaries
of the Tennessee River, also cut their beds to grade in the Ordovician
« Galloway, J. J., Geology and natural resources of Rutherford County, Tenn.: Tennessee Qeol. Survey
Bull. 22, p. 21,1910.
M Lusk, R. G., op. dt., pp. 167-168.
» Galloway, J. J., op. cit., p. 21.