GROUND WATER IN NORTH-CENTRAL TENNESSEE

HOUSTON COUNTY 149
superficial relation to a plain. The flab summit tracts of the divide
between the two rivers, however, are remnants of the plateau, about
775 to 800 feet above sea level. By far the greater part of the county
lies below the plateau level, having been eroded to a submature
stage in the Nashville Basin cycle (pp. 20-22) and subsequently
trenched by youthful streams imperfectly adjusted to the present
stage of the master streams. The total relief is about 475 feet.
The consolidated rocks of Houston County include only the upper
part of the Mississippian series (pp. 33-39). The interstream remnants
of the Highland Eim plateau and most of the lower country in the
eastern half of the county are cut from the massive limestone beds of
the St. Louis limestone and Warsaw formation. The underlying
Fort Payne formation, which in this county is made up of dense thin-
bedded, extremely cherty limestone, crops out in the lower half of
the Wells Creek Basin and forms the valley slopes of Whiteoak, Cane,
and Hurricane Creeks, in the western half of the county. The Ten­
nessee River has cut approximately to the horizon of the Chattanooga
shale along the western boundary of the county, but neither the shale
nor any of the underlying limestones are known to crop out in that
area. On the remnants of the Highland Rim plateau the consolidated
rocks are overlain by a mantle of cherty residual clay and soil, which
at Tennessee Ridge has been penetrated to a depth of 112 feet by a
drilled well. Along the Tennessee River the consolidated rocks are
overlain by clay, sand, and gravel deposited by the stream.
GROUND-WATER CONTHTIONS
In Houston County, as in many other parts of the Highland Rim
plateau in north-central Tennessee, most domestic water supplies are
obtained from dug wells and cisterns in the unconsolidated rocks or
from springs. The dug wells in the cherty clay of the plateau are
generally about 20 or 25 feet deep but range from 15 to 50 feet. Many
of these wells are inadequate during periods of drought, so that rain
water is stored in cisterns as a supplemental or major part of the sup­
ply. A few drilled wells on the plateau tracts find water in beds of
coarse chert debris just above the limestone or in channeled zones
just below the top of the limestone. On the alluvial plains of the
Tennessee River practically all water supplies are derived from dug
wells that pass through a clay hardpan and tap beds of sand and gravel
approximately at the level of the river.
Inasmuch as Houston County is so deeply dissected, the channeled
zones of the limestone have probably been drained in many places,
so that drilling for water is especially uncertain. In general the pros­
pect of finding water is notably less in beds that lie very far below the
level of the perennial streams, and it is unlikely that any water other
than concentrated brines will be obtained at depths exceeding 300
feet.