Crawford. Area, 1000 square miles; population in 1880,
68,607. The last remnants of the lowest workable coal bed along the
Lake Erie outcrop of the Carboniferous system, slowly rising north-north-westward
at the average rate of less than twenty feet to the mile, are seen
in the southern townships of this county, along the low flat summits
of somewhat higher land between French Creek and the branches of Sugar
Creek on the one side, flowing south-eastward and into the Allegheny
River at Franklin, and Crooked and Shenango Creeks further west, flowing
south into the Beaver River. These long and narrow divides are composed
of Pottsville conglomerate (XII,) between the middle and lowest sub-divisions
of which lies the important "block coal bed" of Sharon in Mercer county,
so extensively mined in the State of Ohio; but in Crawford county
this bed is almost everywhere too poor to work, except in East Fallowfield
township, where some of its areas have been exhausted. In James McEntrie’s
mine (1330` A.T.) the bed varied from 4` to nothing, and was covered
by impure cannel or bituminous roof slate, sometimes 6` thick. At
Byhm’s shaft, east of French Creek, (1445` A.T.,) the northern glacier
had crushed it into an unminable condition, and left it covered up
beneath 50` of drift. Crawford county is, therefore, practically destitute
of coal. The lowest member of No. XII is here called the "Sharon conglomerate."
This rock increases in thickness eastward, and becomes the "Garland
conglomerate" of Warren county, and the "Olean conglomerate" of Mckean
county, the outlying outcrop patches of which make those magnificent
"rock cities" along the State line. It is the first of the series
of round-pebble deposits of Carboniferous age. All the gravel
deposits beneath it ("Sub-Olean conglomerate," &c.; Pocono, X)
have flat pebbles. The far end of one of the patches of Sharon
conglomerate caps the hill overlooking Meadville, the upper 35` being
good building stone layers, the lower 10` a conglomerate mass of round
quartz pebbles; and in all exposures in the county what pebbles there
be in the mass are more abundant and larger at the bottom of it. The
frequent honey-combed aspect of the upper layers has been produced
by the decomposition of great quantities of the erect stems of sea-weeds,
and they contain also fish scales and bones in a fragmentary condition.
All round the edges of the patches of Sharon conglomerate crop out
on the hill slopes descending order: Shenango shales, 50`; Shenango
sandstone, 25`; Meadville shales, (including the Meadville upper
fish-bed limestone, 1` thick,) 65`; Sharpsville flags, (including
Meadville lower limestone, 2` thick,) 60`; Orangeville shale,
75`; Corry sandstone, 20`; Cussewago shales, (including a 2` limestone,)
35`; Cussewago sandstone (Butler Co. 1st oil sand,) 25`;
Riceville shales, 80`; Venango Co. 1st oil sand, 20`; blue
shale, 100`; Venango Co. 2d oil sand, 20`; red shales, 15`; blue shale,
125`; Venango Co. 3d oil sand, 30`=TOTAL, 745`; divisible into an
upper group of 435’ of Lower Carboniferous (Pocono X and perhaps Catskill
IX,) and a lower group of 310`, Mr. Carll’s "Oil Sand Group" (perhaps
Catskill, perhaps Chemung, but probably partly both,) as shown by
separate colors on the map. The hill at Meadville is (1548`-1080`
R.R. station) less than 500 feet high, so that the Oil Sand Group
only comes to the surface along the valleys of French, Cussewago,
and Conneaut Creeks in the north-western townships; and the undoubted
Chemung strata (VIII,) underlying the Oil Sand Group, only appears
at the surface along the Conneaut Creek north of Conneautville. Although
the Oil Sands underlie all the rest of the county, and a multitude
of wells have been bored for oil, the only productive area has been
the extreme corner around Titusville. On the flats of Oil Creek, just
outside the county line, Col. Drake bored his famous first well in
1859; and on the flats of Pine Creek, near the Warren county
line, Jonathan Watson, under "spiritual guidance," bored his equally
famous dry well, 3500` deep, stopping (according to a very unreliable
report) in the Genessee (?) or Marcellus (?) black shales. A good
deal of heavy oil was obtained in the vicinity of Titusville. The
3d sand lies about 400` beneath the flats. The curious "grasshopper
excitement" of 1877 is described in Report I3 Carll, 1880,
pp. 422-429, caused by a discovery that about 12,000 barrels of oil
had leaked from the rocks into the drift deposit of the flats. Oil
Creek, like most of the other streams of this region, now flows upon
the upper surface of a deep sand gravel and bowlder deposit which
was left by the northern ice in its retreat. The whole county is covered
with such Glacial drift; and the ancient valleys, which formerly drained
northward into Lake Erie, have been filled up to heights varying from
50` to 350`, so as to reverse the entire drainage of North-western
Pennsylvania, and send the rain-fall into the Gulf of Mexico. There
are no minerals of value in Crawford County, except building stone
and brick clay. Several lakes or ponds produced by dams of drift thrown
across the valleys have become partially filled with a mossy vegetation,
underlaid by a deposit of fresh-water shell marl. The marl which Mr.
Whiting mines above Harmonsburg to a depth of 6` or 8` is known to
be at least 22` deep. Mr. Brown finds peat beneath his marl.
Conneaut lake surface has sunk 25` below the level of the peat bog,
and retired from it to the distance of 1 ½ miles. Its greatest depth
is 100`; its surface lies 497` above that of Lake Erie and 1070` A.T.
From: A geological hand atlas of the sixty-seven
counties of Pennsylvania :embodying the results of the field work
of the survey, from 1874 to 1884. By J. P. Lesley. (Report of
progress (Geological Survey of Pennsylvania), v. X ) Harrisburg, PA
: Board of commissioners for the second geological survey, 1885.
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