GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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32 GEOTJND WATEE <strong>IN</strong> NOETH-CENTEAL <strong>TENNESSEE</strong><br />
Dickson County. (See pi. 4.) In this district no paleonfcologic evi<br />
dence of the age of the formation has been found, so that the correla<br />
tion is based upon the lithology of the material, the geographic rela<br />
tion fco localities at which paleontologic evidence exists, and the<br />
relation of the deposits to the Highland Bim peneplain. The geo<br />
logic map of Tennessee ** (see pi. 4) also shows a small outcrop of the<br />
formation capping the divide between Long Creek and Cross Creek<br />
near Bear Spring, Stewart County. Furthermore, the deposits of<br />
waterworn chert and vein quartz gravel on the Highland Bim plateau<br />
in southwestern Dickson County and adjacent portions of Hickman<br />
County, which are described by Hayes and Ulrich,43 may also belong<br />
to the Tuscaloosa formation.<br />
The Tuscaloosa formation as exposed in a cut on the Nashville,<br />
Chattanooga & St. Louis Railway about 2 miles east of McEwen,<br />
Humphreys County, is described by Wade ** as consisting of about<br />
30 feet of very compact white chert gravel which rests upon weathered<br />
St. Louis limestone. The individual pebbles are well rounded, and<br />
most of them are less than an inch in diameter, although some are<br />
as large as 6 inches. Some sand is mixed with the gravel, although<br />
very little clay is present. The gravel of the Tuscaloosa formation<br />
can generally be differentiated by three criteria from the stream-<br />
terrace gravel with which it may be associated. In the first place,<br />
the individual pebbles and cobbles of the Tuscaloosa formation are<br />
well rounded, and many of them are almost spherical, whereas those<br />
of the terrace gravel are generally flat, elongate, or even subangular.<br />
Small discoidal pebbles of quartzite are abundant in the terrace<br />
gravel at many localities. Second, the Tuscaloosa gravel is composed<br />
for the most part of chert from the Mississippian rocks, whereas the<br />
terrace gravel is derived in large measure from quartzite and sand<br />
stone. Third, pellets of iron oxide are not known to occur in the<br />
Tuscaloosa gravel, whereas they have been observed in the stream<br />
deposits.<br />
The Tuscaloosa is the oldest formation of the Upper Cretaceous<br />
series in the East Gulf Coastal Plain province, although the deposits<br />
that exist in north-central Tennessee probably represent only some<br />
of the uppermost beds of the type section in the vicinity of Tusca<br />
loosa, in central-western Alabama. In north-central Tennessee the<br />
formation was laid down as a coastal-plain deposit along the western<br />
edge of the Cumberland peneplain, underwent planation during the<br />
Highland Rim cycle, and subsequently has been almost wholly<br />
eroded by the Tennessee River during the Nashville Basin and recent<br />
erosion cycles.<br />
« Nelson, W. A., Geologic map of Tennessee, 3d ed., Tennessee Qeol. Survey, 1923.<br />
« Hayes, C. W., and Ulrich, E. O., U. S. Qeol. Survey Qeol. Atlas, Columbia folio (No. 95), p. 1,1903.<br />
« Wade, Brace, op. cit., pp. 103-104.