GROUND WATER IN NORTH-CENTRAL TENNESSEE

30 GROUND WATER IN NORTH-CENTRAL TENNESSEE
QUATERNARY SYSTEM
AIIUVIUM
The master streams of north-central Tennessee and the lower
courses of their larger tributaries are bordered by flood plains, which,
along the Cumberland Kiver, attain a maximum width of nearly a
mile on the concave side of meanders. These plains, which have a
flat transverse profile and terminate abruptly landward against the
rock erosion slopes of the valley, are constructed of alluvium, which
comprises beds of silt, sand, and gravel. The coarser particles of the
alluvium are for the most part rounded fragments of chert from the
Mississippian limestones and sandstone and quartzite pebbles from the
Pennsylvanian conglomerates. The alluvium lies upon normal slip-
off meander slopes or upon the sloping rock sides of a youthful stream
trench, so that the deposits thin rapidly toward the margins of the
plain. They are probably not more than 50 feet thick at most local­
ities.
Without known exception, the alluvial flood plains are subject to
overflow at high stages of the streams, so that they are wholly unsuited
for town sites or industrial developments. Hence the alluvium has
not been developed as a source of ground water, and its water-bearing
properties are not known. If beds of thoroughly assorted gravel exist
below the water table, however, properly constructed wells should
yield large supplies of water. Consequently, these deposits are a
potential but unproved source of ground water wherever the flood
plains can be protected from overflow, so that industrial or suburban
development is feasible.
TEBTIABY(I) SYSTEM (MIOCENE? OB PLIOCENE?)
HIGH-TERRACE GRAVEI
The high-terrace gravel, which Galloway has assigned to the late
Pliocene but which according to Shaw may be as old as Miocene
(see pp. 19-21), occurs here and there in the valleys of the Tennessee
and Cumberland Kivers and their major tributaries as a veneer upon
rock terraces that are as much as several hundred feet above th»3 pres­
ent streams. This old gravel, like the recent alluvium, is composed
largely of waterworn chert from the Mississippian limestones and of
quartzite pebbles from the Pennsylvanian conglomerates. Generally,
however, it is poorly assorted, so that its water-yielding capacity is
not likely to be large. Moreover, the deposits are for the most part
of slight extent and are rather thoroughly drained, and hence they are
not a potential source of large quantities of ground water. Locally,
however, they are likely to yield supplies adequate for domestic use.