GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
GROUND WATER IN NORTH-CENTRAL TENNESSEE
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STRATIGRAPHY 55<br />
near Jefferson, northwestern Rutherford County. The Ridley lime<br />
stone is for the most part a massive, dense light-blue, dove-colored, or<br />
light-brown limestone, which at some places contains abundant<br />
bluish-black or white chert. Locally, as at Sulphur Spring, 1% miles<br />
north of Jefferson, it contains thin-bedded or platy members. The<br />
color of the formation is due largely to the presence of bituminous<br />
matter, the odor of which is usually noticeable when the rock is<br />
freshly broken; at many places it is streaked with granular fucoid<br />
markings of lighter color. The weathered rock is light gray and has a<br />
finely granular appearance, but the weathering does not extend more<br />
than 1 or 2 inches into the rock.<br />
The Ridley limestone can not be discriminated from the older<br />
Murfreesboro limestone on the basis of lithology alone. These two<br />
formations are alike in color, in hardness, and in brittleness; they<br />
contain about the same amount of chert and bituminous matter;<br />
each is platy at a few places; their changes on weathering and their<br />
influence upon topography and soil are identical. Hence the Ridley<br />
limestone can be identified only where it is fossiliferous or where its<br />
contact with the overlying Lebanon limestone or the underlying Pierce<br />
limestone is exposed.<br />
The Ridley limestone is not highly fossiliferous, although Stroma-<br />
tocerium is locally abundant. The most common and diagnostic<br />
species are Stromatocerium rugosum, Camaretta volborthi, Hebertetta<br />
bettarugosa, Gonioceras anceps, Orbignyetta sublamettosa, IAOSJWTQ,<br />
convexa, Rafinesquina minnesotensis, and Protorhyncha ridleyana.<br />
The Ridley limestone is from 95 to 120 feet thick, although most of<br />
the measured sections are between 100 and 105 feet. It crops out<br />
over the greater part of the Nashville Basin peneplain in Rutherford<br />
County and is also exposed in Davidson, Williamson, and Wilson<br />
Counties. (See pi. 4.) In spite of its rather general distribution,<br />
however, complete sections of the formation are exposed at few places<br />
on account of the low relief of the area of outcrop.<br />
PIERCE LIMESTONE<br />
The Ridley limestone is underlain by the Pierce limestone. The<br />
two formations seem to be conformable except at Jefferson, Ruther<br />
ford County, where the contact surface between them is undulating<br />
with respect to the bedding planes. The Pierce limestone takes its<br />
name from Pierce's mill, 19 half a mile south of Walter Hill, Ruther<br />
ford County. It is rather variable in lithology and comprises many<br />
layers of dense blue or gray unfossiliferous limestone between half an<br />
inch and 2 inches thick and one or more massive beds of coarsely<br />
crystalline bluish-gray or brown fossiliferous limestone. The coarsely<br />
w Safford, J. M., op. cit., p. 281.