GROUND WATER IN NORTH-CENTRAL TENNESSEE

42 GROUND WATER IN NORTH-CENTRAL TENNESSEE
similar in lithology to the rock of the type section and is characterized
by species of Heliophyttum, Blothrophyttum, Oystiphyttum, Cyathophyl-
lum, Cladopora, and Bryozoa. Foerste 77 correlated the upper part of
the formation with the Sellersburg limestone of Indiana, which is of
late Middle Devonian (Hamilton) age, and implied that the lower
part was of early Middle Devonian ("Comiferous" Onondaga) age.
Dunbar 78 has correlated the entire formation with the Jeffersonville
limestone of Indiana, which is early Middle Devonian (Onondaga).
The Pegram limestone is undoubtedly separated from the under­
lying strata by a disconformity at the two localities that have been
described.
Recently Pohl 79 has shown that limestone of upper Pegram age is
accompanied locally by an underlying sandstone member, of probable
lower Pegram age, whose maximum known thickness is 35 feet. He
describes the type section and occurrence of this member as follows:
Section in district 4, Trousdale County, Term., in road cut on hill 1% to 1% miles
southwest of Valentine's store
Mississippian:
Chattanooga shale Feet
Dead-black, thinly fissile shale with thin bed of conodont-bearing
sandstone at base__.___ To top of hill.
Gray blocky shale carrying abundant Lingulas and
a few Mississippian conodonts________________ 7
Possible break.
Devonian (?): Black shale like first with lenses of fine, black
sandstone near base, grading without apparent break
into limestone below--______-__________------- ___ 8
Devonian:
Pegram limestone (Sellersburg formation) Dark-
brown semicrystalline limestone carrying numerous
large heliophylloid corals, becoming purer gray below
and very conglomeratic (semiedgewise) near base. _ About 4
Pegram limestone (Jeffersonville formation) White,
brown, or pink coarse sugary sandstone, very f ossilif er-
ous at top; barren and exhibiting extremely unsettled
conditions of deposition in lower 4 feet. Fauna: Lep-
taena rhomboidalis, Stropheodonta aff. S. hemispherica,
Stropheodonta demissa, Leptostrophia aff. L. perplana,
Schuchertella sp., Spirifer cf. S. varicosus, Cystodictya
gilberti, Fenestella sp., Rhipidomella aff. R. vanuxemi,
Hadrophyllum orbignyi, Chonetes aff. C. mucronatus,
Centronella? glansflagae cf. Pholidostrophia iowensis,
Polypora sp., Loculipora sp., Cystodictya sp., Anibo-
coelia sp., crinoid stems__________________________ 9
Silurian: Niagaran. Formation undetermined.
« Foerste, A. F., op. cit. (1901), pp. 425-426.
w Dunbar, C. 0., op. cit., p. 91.
» Pohl, E. R., personal communication, February 6,1929.