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

60 ILLINOIS BASIN COAL RESOURCES
limestone and coal beds. This may account
for the local absence of No, 6 coal in Edwards
county (T. 2 and 3 S., R. 10 E.),
just as it does for local absence of the coal
bed in Saline County.Vhe electric-log
pattern of the Anvil Rock sandstone is
typical of Pennsylvanian sandstones, with a
fairly high resistivity and potential strength.
The composite pattern produced in electric
logs by "No. 7" coal bed, the Bankston
Fork limestone, the Anvil Rock sandstone,
and the Herrin limestone and coal beds in
the Illinois basin has been previously dexribed,l0
although the Bankston Fork
limestone is shown in none of the diagrams.
In control well No. 7 (fig. 8) it is believed
that both the Bankston Fork limestone and
Anvil Rock sandstone are present.
Since both the Bankston Fork limestone
and the Anvil Rock sandstone are discontinuous,
their places often being occupied
by shale, the pattern of electric logs shows
great variability between "No. 7" coal bed
and the Herrin limestone.
No. 5A coal bed.-The Briar Hilll1 or
No. 519 coal bed lies between No. 6 and
No. 5 coal beds, usually between 25 and
30 feet above the lower bed, but there is
a good deal of variation. It has a thickness
oi 1 to 3 feet and is overlain by 1 to 2 feet
of black "slate." A limestone caprock
above this coal bed or "slate" is a rare occurrence.
The No. 5A coal bed is recorded
in 8 control drill holes (No. 31,
fig. 8; Nos. 2, 5, 91, fig. 9; Nos. 6, 7, 8,
106, fig. 10). Inspection of available electric
logs of these holes shows that the position
of the coal bed is commonly marked by
a low peak in the third curve, a reverse
peak in the third curve opposite a low
bulae in the self-potential curve (No. 34,
fig. 8; Nos. 7, 8, fig. 10). The recurrence
of this combination of patterns at the appropriate
position in many electric logs of
Edwards County drill holes indicates that
"Cady, G. H. Coal I-esnurces of District V (Saline and
Gallati? roi~nties): Illinois Gcol. Sr~rvey Min. Inv. Bull.
19. n. 21. 1919.
lo See footnote 4.
IIJdee. Wallace, Geology of the ICen~uck~ part of the
Shan neetov n clr~ndranglc Kcntucky Gcol. Survey, p. 3 5,
1916.
this thin coal bed is rather widespread. In
some logs the pattern of the normal curve
is less characteristic and may merge with
that of beds above and below, but the reentrant
of the third curve is almost invariably
in evidence (No. 31, fig. 8). The
position of No. 5A bed between No. 6 and
No. 5 coal beds detracts from its importance
as a key bed.
Between No. 6 and No. 5A coal beds
there is usually a massive sandstone (Nos.
9, 11, 34, fig. 8; Nos. 3, 91, fig. 9; No.
8, fig. 10) well developed in outcrop at the
same stratigraphic position near Absher Post
OGce in southeast Williamson County and
in the town of Equality, Gallatin County.
Beds below hlo. 5 coal bed.-The graphic
logs of the control wells (Nos. 9, 11, 34, fig.
8; Nos. 2, 91, fig. 9; Nos. 8, 106, fig. 10)
show at least three fairly prominent beds in
the lower part of the Carbondale group.
Of these the upper two are thin coal bedsabout
equally spaced, 75 to 125 and 160
to 220 feet below No. 5 coal bed. The
upper of these has been designated "No.
4" in the present series of studies.
The "No. 4" coal bed, which is apparently
not over 3 feet thick and probably generally
less, is overlain by black "slate" and
in some places by a thin bed of limestone.
In electric logs these beds usually have a
very characteristic double-peak pattern
(Nos. 3, 91, fig. 9), apparently because of
the association of thin limestone and coal.
In some logs the pattern is a single peak
on the normal curve and a reverse third
curve peak similar to that of coal 5A (No.
31, fig. 8; No. 8, fig. 10). The frequent
presence of such a pattern at the appropriate
position in electric logs indicates that these
beds are generally present in this county.
This bed, although occupying a position
approximately the same as that of the
Sumnium (No. 4) coal bed of western
Illinois and that of No. IV coal bed in Indiana,
has not been proved equivalent to
either.
The second coal bed, about 50 to 100 feet
lower, is characteristically marked. It was
encountered in 8 of the control drill holes
(Nos. 9, 11, 31, fig. 8; Nos. 2, 3, 91, fig.
9; Nos. 8, 106, fig. lo), and its position in