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

HB&lILTON COUNTY 103
bed of limestone was penetrated 290 feet
above No. 6 coal bed. Apparently no single
drill hole in Hamilton County is known to
have penetrated two beds of limestone at
the two positions. It is suspected that one or
both of these limestones may represent the
West Franklin limestone, but this has not
been established. The position of these limestones
relative to the thin coal beds noted
in the preceding paragraph is not evident.
Like the West Franklin limestone to the
east, the Cutler limestone is widespread
west of Hamilton County. Usually in
Franklin County and westward the Cutler
limestone lies immediately above a black
shale or "slate" which in turn overlies the
Cutler coal bed. If the Cutler limestone
is present in Hamilton County, it lies at a
greater interval above the Cutler coal bed
than is usual farther west. In the southwestern
half of the county the first limestone
lies 15 to 25 feet above the Cutler
coal bed (fig. 22, Nos. 1, 4, 6, 9, 19, 21)
or 95 to 130 feet above No. 6 coal bed.
The variation in interval suggests that more
than one lenticular bed of limestone may be
present at different stratigraphic levels. As
yet definite correlation is impossible. Therefore
the-Cutler limestone does not have the
same value as a key bed in Hamilton County
as it has farther west. Cuttings from the
limestone or limestones at this general position
are light gray to tan, white to light
gray to tan, and slightly granular to fine.
The recorded thicknesses are from 3 to 6
feet.
Limestones at the position of the
Cutler are missing from the succession in
the northeastern half of Hamilton County.
A thin coal bed lying a short distance
above the Bankston Fork limestone, and
between this limestone and the Cutler coal
bed, is reported in the logs of three drill
holes: County No. 6 (sec. 34, T. 5 S., R.
5 E.) ; County No. 46 (sec. 33, T. 4 S.,
R. 6 E.) ; and County No. 478 (sec. 26, T.
4 S., R. 7 E.). The coal bed is overlain
by a thin bed of black shale and may represent
the Bankston Fork coal bed of Saline
County.*8
A thin bed of black shale and a thin bed
of coal are reported in some records within
IS Cady, op. cit. (Areal geology).
a few feet above the Herrin limestone.
This is the position of the Jamestown coal
bed of Perry County.lg The Jamestown
coal bed is commonly overlain by a bed of
limestone up to 2 feet thick closely resembling
the Herrin limestone. Usually the
Jamestown coal bed is either absent or is
not recognized. It has been suggested that
this* coal bed is equivalent to the much
thicker No. 12 coal bed of Kent~cky.~'
Because it is difficult to recognize, it cannot
be regarded as an important key bed.
Within the Carbondale group there are
several thinner beds in addition to the key
beds No. 6, No. 5, and "No. 4." Briar
Hi1121 (NO. 5A) coal bed, in places accompanied
by a thin bed of limestone, is
generally reported between No. 5 and No.
6 coal beds. On the basis of information
obtained from two control drill holes on
the Carbondale group, Nos. 42, 478 (fig.
21), it appears that a thin bed of coal lies
50 to 60 feet below "No. 4" and a second
coal bed about 100 feet below, or 200 to
260 feet and 240 to 300 feet respectively below
the top of No. 6 bed. The upper of
these beds may represent the LaSalle "No.
2" coal bed of northern Illinois. The difficulty
in recognizing the position of these
thin coal beds in electric logs makes them
unsatisfactory as key beds.
The base of the Carbondale formation
is marked by the fairly conspicuous Palzo
sandstone commonly present about 300 feet
below No. 6 coal bed. It is porous and is
commonly marked in electric lcgs by a fairly
high resistivity and an accompanying high
potential. Like most Pennsylvanian sandstones
it varies considerably in thickness and
cannot always be identified. Further difficulty
arises because of the presence of a
succession of lenticular sandstones in the
underlying Tradewater formation, the
upper ones of which may be indistinguishable
from the Palzo sandstone.
1"ell. Ball, and McCabe, op. cit.
20 Weller, J. M., and Wanless, H. R Correlation of
mineable coals of Illinois, Indiana and we'stern Kentucky:
Bull. A.A.P.G., vol. 23, No. 9, p. .1391, Sept. 1939.
'1 wanless, H. R., Pennsylvama cycles in wester11 Illinois:
Ill. Geol. Survey Bull. 60, pp. 79-83, 1931.