GROUND WATER IN NORTH-CENTRAL TENNESSEE

OCCURRENCE OF GROUND WATER IN LIMESTONE 85
is considered an excellent water bearer, and many limestone wells will yield from
100 to several hundred gallons a minute. Where these same formations are so
deeply buried that they have never been leached they are often not regarded as
aquifers by deep-well drillers, who search for the water-bearing sandstones
between the limestones.
The relation between solution caverns in the limestone and the
physiographic history of the Mammoth Cave district of Kentucky is
described by Lobeck.58
Generally the sequence of events in the geologic and physiographic
history of north-central Tennessee has not been such as to cause the
immersion of any extensive bodies of cavernous limestone in the zone
of saturation. Instead, that region has been uplifted recurrently, so
that the cavernous limestones have been in part drained by rejuve­
nated streams and by deeper ground-water conduits. Hence the
capacity of wells and springs that issue from these rocks is limited.
Furthermore, in areas where the water table has been depressed below
the cavernous portions of the limestone, water is not usually confined
under artesian head. In a few small areas of north-central Tennessee,
however, the water table has been raised so much as to saturate
cavernous rock and to produce artesian conditions (pp. 96-98), proba­
bly because a major ground-water conduit became dammed through
deposition of silt, collapse of its roof, or some other cause.
Where the water table has been depressed slightly below a body of
cavernous limestone, either by uplift of the earth's crust or because
the stream to which the water table is adjusted has eroded its bed
downward, a lower equilibrium profile of solution is established.
Consequently a new set of solution channels tends to form at that
level. In many places the lower channels tend to follow the same
joints as the upper channels and to join themselves to the upper chan­
nels by vertical solution channels or natural wells. Ultimately the
chaHEtete of the upper set would be drained except when water flowed
through them in passing to the water table. If the water table were
depressed several times and the interval between successive de­
pressions were long enough for solution planation to become extensive,
the body of limestone would be ramified by dry caverns at several
levels, whereas the water table would be far below the surface. On
the other hand, each cycle of solution channeling might be interrupted
at any stage, so that many complex conditions with respect to size and
pattern of water-bearing openings might result. Conditions of this
sort occur very commonly in the valleys of large streams that have cut
downward by several stages, in each of which a local equilibrium profile
of erosion and a correlative equilibrium profile of solution have existed
temporarily.
*' Lobeek, A. K., The geology and physiography of the Mammoth Cave National Park: Kentucky Qeol.
Survey Pamphlet 21, pp. 41-47,1928.