GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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<strong>GROUND</strong> <strong>WATER</strong> JN NO^T^-^^EUAL <strong>TENNESSEE</strong><br />
of the Highland Rim plateau (pp. 16-18). Its. naajoF ridge crests,<br />
remnants of the Highland Rim peneplain, increase in altitude from<br />
about 800 feet above sea level in the northwestern part of th» county<br />
to 1,020 feet in its southwest corner. None of these remnants are<br />
extensive, however, for the peneplain has been dissected^ by the<br />
closely spaced youthful valleys of a dendritic drainage pattern.<br />
Hence the topography is rather rugged, especially along the. southern<br />
boundary of the county, where the Harpeth and Duefc Rivers are<br />
striving for drainage mastery. The eastern half of the county, which<br />
constitutes a. part of the northern lobe of the Nashville Basin (p.<br />
18), is drained northward by the Harpeth and West Harpeth Rivers.<br />
In their lower reaches these s»fereams kave; planed laterally and have<br />
cut valley floors half a mile to 3 miles wide at 620 to 670 feet above<br />
sea level, a stage which is correlative with the much more extensive<br />
planation by the Stone River in Rutherford County. Furthermore,<br />
they have reduced the interstream tracts to groups of submature hills<br />
and branching ridges, the bjghest of which, are in $he south-central<br />
part of the county and range from 1,165 to 1,250 feet a^oye se^ level.<br />
These hilly tracts are outliers of the Highland Rim plateau.<br />
The rocks that crop out in WiUiamson County constitute a rather<br />
full stratigraphic sequence from the St. Louis and Warsaw Hmestones<br />
of Mississippian age, to. the, Lebanon Uinestone,, of Lower Ordovician<br />
age (pp. 33-54). The youngest stratigraphic unit, which comprises<br />
the St. I*ouis and Warsaw limestones, is made up of thick-bedded,<br />
somewhat cherty limestone and craps out over an extensive tract<br />
along the western boundary of the county. It also caps the Mgher<br />
ridges a.a far eastward as the. Highland Rim escarpment but. is not<br />
known at any point east of the West. Harpetk River. (See, pi. 4.)<br />
However, visible exposures of the rock generally occur only qn the<br />
slopes of youthful valleys, for on the remnants of the Highland Rim<br />
peneplain it is overlain by residual clay and chert as much as 60 feet<br />
thick. The Warsaw limestone is underlain everywhere by the Fort<br />
Payne formation, which comprises thin beds of extremely cherty<br />
limestone and shale, sandy limestone, calcareous shale, and clay shale.<br />
These beds also 0ap outliers of the plateau in the north-central and<br />
sotuthrcentiral pajts of the county as well as the highest summits oj t|ie<br />
ridge that trends southeastward across the county between the<br />
Harpeth and West Harpeth fivers. In a few places,, as oa the slopes<br />
o$ Sugar- Riclge, in the south-central part, ol the county, thefije beds »?$<br />
underlain by the New Providence shale, wflich consists of clay, sjiale,<br />
ancj lenses of massive, crinoida) limest,one. The Fort Payne formation,<br />
or the New Providence shale where that, formation is pyesen^ is under<br />
lain in all p&rts, of the county by the carbonaceous Cnattanqoga,<br />
sh,aje. This alrftbigr^pjbic horizon marker crops out as a narrow bancj<br />
in tine lowe? part of t&e Highland Rim escarpment and ifcg