Grant County herald. [volume] (Lancaster, Wis.) 1850-1968, 1878-03-14
GEOLOGY OF THE LEAD REGION.
FIG. 10.
CINCINNATI GROUP.

| CINCINNATI GROUP.
| Geographical boundaries. This for
nation was found to cover muc.
larger area of country than had pre-
viously been supposed. 1t appears il
I. l, r. 2, E., and has an area o
about five square miles, contained il
the following sections: 81, %, %, "a
25, 26, 81, %, 81, 35 and SO. In T
l, r 3, E., it is found in Secs. 81
and 81, covering about one square
mile. 1t does not occur north of Il
/, on ranges and 8 E.
| Near the corner of Secs. %, 23, q
and 81, T. l, r, 2, E., the formation
attains an elevation of nearly 600 feel
above Lake Michigan; and from here
to Scales Mound village it forms q
continuous chain of hills, among
which the most noticeable is Charles
Mound, which is the highest land in
the state Of Illinois. The mound is
capped with abont so feet of Niagara
limestone, and in one place a quarry
has been opened, from which speci-
mems of the fossil Fafosites fdvosa
have been obtained [See Fig. 10.
The Cincinnati group next appears
about the Platte Mounds, in the
southern part of T. 4, r. l, E., and
the northern part of 7. 8, Il. L, E. In
I 4, r. l, E., it is found in Secs. 81,
80, SO, "a, IS, SO, covering an area of
nearly three square miles, and reach
ing an elevation of LAO feet above
the sea.
The formation also exists in its full
thickness at the Blue Mounds, but ex-
posnres of it either natural or artificial
are seldom visible some of the clay
which characterizes the lower part of
the formation was found on the Brig
ham farm at the East Mound.
No exposure of this formation was
found at these localities. In passing
over the gradual slope of the mounds
it is impossible TO distinguish any
boundary line between the Cincinnati
group and the underlying Galena
limestone, such as is seen on the level
table land south of Shullsburg, which
has been formed by the denudation of
the soft shales which the harder lime
stone has to great extent escaped
The line OF demarkation between the
shales and the everything Niagara lime
stone, is well defined at the West
Platte Mound on all sides by the very
marked change from the steep slope
OF the limestone to the comparatively
gentle one fthe shales. On the north
side of this mound, lodges of the Nj
agara limestone may be seen in place
almost to the bottom of the formation.
The Cincinnati group was also
found covering about seven square
miles Of country, about the Sinsinawa
Mound, in the following sections: l,
IL, IS, IA, "a, 25, 20, 35, SO, T. l, r.
2, w. Secs. 6, 7, s, l6, II, ls, 10,
20, 20, 80, 81, I. l. r. l, W., extend
ing north from the Sinsinawa Mound,
as far as jamestown. Nearly all the
mines on the ridge north and east of
Fairplay are sunk through the lower
part OF the Cincinnati group, and
good specimens of Nucula fecunda
may often be found in the dirt thrown
out OF the shallow holes, when the
clay has not been covered again by
the refuse of deeper workings.
Theological Characteristics. The
strata OF the Cincinnati group are
very regularly and conformably de
posted, and do not exhibit any indi-
cation of sudden and violent disloca-
tons, faults, or uplifts.
The lower beds of the formation
are very finely laminated, and of a
dark blue color, in many places be-
coming green and brown. The up,
per layers are of yellowish color,
and more or less calcareous and sill
cious.
The lower and middle members of |
the group split readily andwith very
smooth face, but the upper layers,
though quite thin-bedded, present
rough and uneven appearance. This
group nowhere presents beds of suffi-
GENTLY thick and durable stone tor
building purposes. Only one place
was noticed where an attempt had |
been made to quarry this rock it had
been abandoned as impracticable, af-
ter small amount of work had been
done.
Where undisturbed. this group has
a thickness of about 125 feet. This is
the case only on the mounds, which
are still capped with the Niagara
as in all other places it has
been more or less removed by denu-
dation.
There is nowhere a good natural
exposure of the formation. The rocks
tic YIvup vuut % a,vs.o
resistance to the weather that they do
not appear in rugged cliffs, such as
are seen in all the formations which
underlie them, but usually in gently |
hills. The best exposure |
is the one in the cut of the Illinois
Central railroad, near Scales Mound
Station, of which very accurate Sec
ton has already been given in Prof.
Halls report. 1t is much more accu-
rate than can now be obtained, as the |
weather has since then so decomposed |
the friable shales that only few feet
of the lower beds are now visible, as
they we're originally presented. As a
general guide to the formation, we
take the liberty of producing it:
Fl. In. |
1, Greenish shale, with alterations
of calcareous and silicious layers,
few inches in thickness. $500. 81
2. Green silico- calcareous and argyll
laceous shales. IL 81
8, A silico-calcareous or magnetism
4. Greenish shale as above. ....... II :.
s. Concrecionary layer, one to three
inches.
6. Shale with Li,galla. ......... =.
I. A layer filled with small Nuc,da,
and known as the Nacada bed
four to eight inches. .......... ;. 8
s. A calcareous band cut by open
Joints or assures. into which the
materials of the layer above have
penetrated ..................
9. Dark olive shales, finely laminat-
ed and destitute of fossils. ..... 3
10. Nucula bed, similar to the above,
four to six inches. ....... 8
49,