subsurface geology and coal resources of the pennsylvanian system ...

EDWARDS' COUNTY 55
No records of diamond-drill holes in are indications that the benches of the West
Edwards County are available in the Sur- Franklin limestone may be more widely
vey files, although it is probable that struc- separated than usual. In hole No. 3 the
ture test core holes have been drilled by oil
companies here and there.
Should diamond-drill cores of considerable
thickness of the Pennsylvanian system
eventually become available for study they
distance from the top of the top bench to
the base of the bottom bench is 45 feet,
and in hole No. 6 possibly as much as 98
feet. In the latter hole a thick shale, variegated
near the top and bottom, lies between
would provide a much improved under- the two lower benches. It is, of course,
standing of the stratigraphic succession and
also make usable as key beds strata in the
possible that this lower limestone actually
lies below the West Franklin.
upper part of the McLeansboro group above At least seven of the control drill holes
the West Franklin limestone and other (]hTos. 1, 34, fig. 8; Nos. 2, 91, fig. 9; Nos.
strata in the Tradewater and Caseyville 7, 8, 106, fig. 10) found the Ditney coal
groups. Even for the present report cer- bed3 or black shale at the same general
tain of these strata are helpful in establish- horizon, a few feet above the West Franklin
ing the position of faults, although they
cannot be identified with certainty throughout
the county.
limestone. When three limestone benches
West Franklin limestone.-In the 14
control drill holes in this county (figs. 8, 9.
lo), the West Franklin member, whether
in one, two, or three benches, has been found
from an examination of the cuttings to consist
of light gray, buff, or brown fossiliferous
very finely crystalline limestone, and of
various kinds of associated shale, and is not
particularly different from several other
McLeansboro limestone beds.
The upper
bench is commonly 3 to 4 feet thick, and
is separated from the middle bench by 1 to
2 feet of light gray carbonaceous and
micaceous shale. The middle bench has an
average thickness of about 10 feet, and the
lower bench is usually 3 to 5 feet thick.
The interval between the two lower benches
is usually 5 to 10 feet and is occupied by
shale which, at least in some places, is variegated-reddish,
green, gray, and ello ow. It
is usually of an unctious, slip-fracture type,
similar to underclay. Variegated clay shale
of much the same character is also present
in some places for a few feet below the
lower bench of limestone. In one control
drill hole (No. 91, fig. 9) variegated shale
was reported above the upper of two limestone
benches and clay shale between the
benches, The position of the red shale is
therefore not a completely reliable criterion
for the identification of the individual
benches of the limestone in this county.
In the logs of ts~7o of the control drill
holes (No. 3, fig. 9; No. 6, fig. 10) there
are reported the Ditney coal bed occurs
within about 5 feet above the limestone
(Nos. 7 and 106, fig. 10) ; when two
benches of limestone are reported the coal
bed is within about 5 feet of the limestone
(No. I, fig. 8), or it may be separated
from the limestone by an interval that
exceeds 10 feet (No. 31, fig. 8 ; No. 91, fig.
9; No. 8, fig. 10). The coal bed does not
seem to be present in holes in which only
one bed of limestone was reported (No.
11, fig. 8; No. 5, fig, 9; No. 6, fig. 10).
At the position of the West Franklin
limestone electric logs usually show one
pronounced resistivity peak in the normal
curve, with minor peaks above and be!ow,
one or both of which may be absent. Four
logs (Nos. 1, 3, 5, 8, figs. 8, 9, 10) show
a single peak, although in holes Nos. 1 and
9 two benches of limestone were reported.
Two holes ( Nos. 34, 91, fig. 8) show two
peaks corresponding to the two limestones
recorded. In one hole (No. 34, fig. 8) the
lower peak is the higher, and in No. 91 the
upper peak is the higher. In both holes the
higher peak is opposite the position of the
thicker limestone. Hole No. 8 (fiy. 10)
shows a single peak opposite the thicker of
two limestone benches. For the single
hole with the three limestone benches (No.
9 fig. 10) for which an electric lo,g is available,
there are three peaks on the normal
curve with the highest peak opposite the
thickest limestone bench. In general the
V~ulIer, 14. L., and Ashley, G. H., U. S. Geol. Survey
Genl, Atlas, Folio No. 81. Ditney, Ind., p. 2. 1902.