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

70 ILLINOIS BASIN COAL RESOURCES
as datum planes in the delineation of the of other drill holes to be useful as local
structure of the Pennsylvanian rocks. It kev strata.
is expected that the information assembled
MCLEANSBORO GROUP
will assist those officials who are responsible
for protecting the workable coal beds
against encroachment of any kind through
abandoned drill holes, that it will be of
service to those interested in the exploration
and exploitation of the coal resources
of the region, and that it will provide
structural infoi-mation which may aid in oil
and gas exploration. Finally, and more
academically, we hope that it will result
in an improvement in the understamding
of the stratigraphic succession of the
Pennsylvanian system in the southern part
of the Illinois coal field.
In addition to the individuals mentioned
in the introductory paper, special acknosvledgment
is made of the assistance in correlations
and in structural interpretations
given by David H. Swann and E. P. Drr-
Bois of the Oil and Gas Division, H. A.
Lowenstam of the Coal Division, and in
the interpretation of electric logs by Carl
A. Bays of the Groundwater and Geophysical
Exploration Division.
PENNSYLVANIAN KEY BEDS
The widespread Pennsylvanian key beds
of the Illinois basin discussed in the introductory
paper (pp. 9 to 26)-Shoal
Creek limestone, West Franklin limestone,
"No. 7" coal bed, Herrin limestone and
Herrin (No. 6) coal bed, and the Harrisburg
(No. 5) coal bed-are all present in
that part of Gallatin County described in
this report. However, much of the area is
underlain only by beds older than the Shoal
Creek limestone, so that it is a key bed in
only a relatively small part of the area.
The West Franklin limestone and "No. 7"
coal bed are not continuous and are recognizable
only in limited areas, so that they
also serve little purpose as key beds. Certain
coal beds, particularly "No. 4," "No.
2," and the Davis bed, are sufficiently videspread
and definitely recognizable in both
control drill holes and in the electric logs
Shoal Creek li7i~estone.-The Shoal Creek
limestone outcrops in the town of New
Haven in northwest Gallatin County (Loc.
No. 9). It appears equivalent to the limestone
outcropping along Shoal Creek in
Bond County. " '
The Shoal Creek (New Haven) limestone
also outcrops in the northeastern end
of the Shawneetown Hills (Sec. 9, T. 10 E.,
R. 9 S. (No. 89). In addition to a small
undetermined portion of the Shawneetown
Hills, this limestone underlies a n-edgeshaped
area between the township line running
north from the town of Ridgeway and
an imaginary line extending northeast from
Ridgeway to New Haven. Drill holes in
this area usually encountered the limestone.
The Shoal Creek limestone in outcrop has
lithologic characteristics common to several
Pennsylvanian limestones, particularly to
those of the upper part of the Pc4cLeansboro
group, and is bluish gray to gray on fresh
surfaces and brownish where weathered.
The rock itself is mostly close textured and
dense, relatively pure, and if crystalline,
only very finely so, The usual nodular
structure of McLeansboro limestones is
evident in certain parts of the member, and
thin argillaceous partings give a semblance
of irregular bedding in the lower part.
The rock exposed at New Haven possesses
no physical cha.racteristic that distinguishes
it from the West Franklin limestone except
possibly its fairly characteristic thickness
of only 3 to 7 feet and its occurrence in a
single bench. Like many other limestones
it is often underlain by black more or less
sheety shale or "slate." It is not conspicuously
fossiliferous, but brachiopods
and crinoid stems are present. The
range of the interval between the Shoal
Creek limestone avd No. 6 coal bed is 500
to 566 feet.
The Shoal Creek limestone (fig. 12) is
recorded in electric logs by a pronounced
Uclden, Jon A,, Notes on the Shoal Creek limestone:
Illinois Geol. Survey Bull. 8, pp. 117-126, 1907.
" Cady. G. I-I., Sienificant u!lcertainties in Pennsylvanian
col-relation in the Illinois has~n: Bull. Amer. Assoc. Pet.
GeoI., vol. 20. no. 10. pp. 1507-1524, 1929.