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

EDWARDS COUNTY 6 7
of 300 to -1-00 electric logs of drill holes
located in the county it appears that the No.
6 coal bed is generally present.
Black shale ("slate"), not more than
about 2 feet thick, is generally reported
above the coal bed. No black shale was
reported in the record of the drill hole (No.
34, fig. 8) showing 5 feet of coal. Difficulty
in differentiating black "slate" and
coal while the holes are being logged is
acknowledged. Some of the thickness may
be "slate," but the presence of "slate" is
usually revealed in the cuttings, and this is
considered in the estimates.
Above the black "slate" there is usually
a limestone caprock. Aside from the depth
and thickness of the bed, mining conditions
would probably be favorable. For some
time to come these important factors will
stand in the way of commercial exploitation
of the No. 6 coal bed. Diamond drilling
may some day prove that the present
estimates are too conservative.
The data at hand seem to indicate that
No. 6 coal bed has an average thickness of
at least 3 feet for the area of the county
(238 square miles), representing a tonnage
of approximately 713 million tons, on the
basis of one million tons per square mile
per foot. The depth of the bed ranges
from SO0 to 1050 feet.
Harrisburg (No. 5) coal bed.-The- No.
5 coal bed was penetrated in eight control
drill holes between 82 and 116 feet below
No. 6 (figs. 8, 9, 10). In seven of these
holes the bed was 4 feet thick, in the remaining
one, 3 feet. It was apparently present
in all the control drill holes that were
logged through the lower McLeansboro and
upper Carbondale beds. The thickness of
the No. 5 bed seems to be sornewhat greater
than that of No. 6 and the bed also seems
to be more widespread. A caprock limestone
is reported only occasionally. Black
shale, 1 to 5 feet thick, is usually present
above the coal bed, and above this there is
usually a considerable thickness of shale or
siltstone. Assuming that the bed has an
average thickness of at least 3 feet, for
which there seems to be good evidence, the
reserves represented by this bed amount to
nl~nost 714 million tons. Thus the esti-
mated amount for the two beds agrees with
the formes estimate of 1.2 billion tons.
The depth of the No. 5 coal bed ranges
in the control holes from 916 to 1136
feet. At this depth it has been assumed
that a coal bed should have a thickness
of 3$4 feet to be workable. It is
possible that the thickness of No. 5 bed
usually attains this minimum.
Coal beds below No. 5.-Data have been
presented (table 7, figs. 8, 9, 10) showing
that beds of coal believed to be 3 to 4 feet
thick have been penetrated in drilling at
various levels below No. 5 bed. On earlier
pages the "No. 4," "No. 2," Dekoven, and
Davis beds have been described or mentioned,
but better evidence of their thickness
and distribution awaits improved methods
of drilling or recording thicknesses of
Pennsylvanian beds in rotary-drill holes
or core drilling. The amount of coal in
these deep-lying beds is not estimated.
Two analyses have been made of coal
samples collected from rotary-drill hole No.
121 in Edwards County (table 1). As
stated in the introduction, these analyses
are not strictly comparable with those made
from standard face samples of coal collected
in a mine.17 When delivered to the laboratory,
the sample is roughly separated from
foreign material by using a separating liquid
of 1.50 sp. gr. The float material, which is
largely coal, is then washed to remove the
film of drilling mud, dried, and then delivered
to the chemical laboratory for analysis.
The material analyzed is therefore a
relatively clean and somewhat air-dried coal
and may be equivalent to fairly well-prepared
coal. The analysis probably shows
somewhat lower moisture, ash, and sulfur
zontents than are present in the coal beds,
and higher "as received" and "moist, mineral-matter-free"
B.t.u. values. The unit coal
values may be more nearly correct, and these
are relatively high, resembling those of No.
5 coal bed in Saline County. Sulfur values
are of particular interest and are relatively
high. It has been pointed out (p. 13) that
Holmes, J. A., The sampling of coal in the mine: U. S.
Bur. hlines, Te-h. Paper No. 1, 1918.