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PAST AND PRESENT OF PIKE COUNTY. 39
walls twenty or thirty feet high when cut through.
F,rom seventy-five to eighty per cent of it is silica,
the dead shells of our ponds and bayous. It also
affords a variety of chalky lumps and masses
in New
which assume many imitative forms, as of potatoes
and the disks called "clay-stones"
England. It also gives origin to the bald knobs
so frequently met with along the river bluffs, and
is often rounded into natural mounds which have
been very generally used by the Indians as burial
places. The bones of extinct animals are often
found in the marly beds of this formation, along
with land and fresh-water shells.
This deposit consists of variously colored clays
containing gravel and boulders. It underlies the
loess, and hence is not visible along the bluffs.
In the interior of the county it is often penetrated
by well-diggers. It thins out toward the bluffs.
At the base of the drift near Barry there is a bed
of clean, yellow flint gravel, partially cemented
by iron oxide into a ferruginous conglomerate.
ECONOMICAL GEOLOGY.
Pike county has an abundance of building
stone. The Niagara limestone near Pleasant Hill
furnishes a buff magnesian rock, in very regular
beds, fully equal in quality to that of Grafton and
Joliet. Part of the stone in the public-school
building at Pittsfield was brought from Joliet,
while stone just as good and beautiful was outcropping
within ten miles of that town. "A want
of the knowledge of this fact," says Mr. Worthen,
"has probably cost the citizens of Pike county far
more than their proportion of the entire cost of
the geological survey of Illinois."
3
The Burlington limestone, which outcrops over
a wide area in this county, will
furnish an unlim-
ten to fifteen per cent alumina and iron peroxide,
ited supply of excellent building stone. It is
three to four per cent lime, and one to two probably not less than 150 feet thick. The more
per cent magnesia. In the vicinity of Chambersburg
flinty portions are the best material for macaderywhere
it furnishes a the loess is sixty to seventy feet thick. Evamizing
roads. Near Montezuma is a ten-foot
light, porous sub-soil, bed of excellent dimension stone. Similar beds
which is admirably adapted to the growth of fruit are exposed on Big Blue creek four miles southeast
of Pittsfield, where they are forty feet thick,
trees, vines and small fruits. In some places it
contains a variety of fossil shells which present
the usual bleached and water-worn appearance of
containing masses two to four feet in thickness.
On the west side of the county it forms an almost
continuous outcrop, ten to forty feet thick, along
the river bluffs ;
and on the east side of the county
it also forms a continuous outcrop in the bluffs
from Griggsville Landing south.
The lower portion of the Keokuk limestone is
fully as useful as the preceding.
Excellent quarries
are worked two miles north of Griggsville
on the south fork of McGee's creek. The stone is
composed almost entirely of the joints and plates
of crinoids, cemented together by a calcareous
paste.
The St. Louis group, although limited in extent,
furnishes some good building stone, mostly
found in Perry township and vicinity, as already
described.
The coal deposits in this county are all, except
at Huntley's place, too thin for profitable working.
Where surface "stripping," however, can
be done, it pays to mine the thinner deposits.
Huntley's is probably a local deposit, a "pocket,"
which will soon be exhausted.
No mineral ore, except a little iron, has been
found in Pike county.
The Burlington and Keokuk groups furnish
the best of material for quick-lime. The St.
Louis group, which is generally preferred, is very
limited.
Good hydraulic limestone for cement can be
obtained from the Kinderhook group.
Fire clay, which usually underlies the coal,
can be mined with coal to advantage. The brown
clays of the drift and the loess furnish superior
material for brick.
For marble the bed of oolitic conglomerate of
the Kinderhook group at Rockport furnishes a
stone capable of a fine polish and makes a beautiful
variegated marble ;
but the bed, so far as ex-