Cambria. - Area, 670 square miles; population in 188046,811. Four
fifths of the lozenge-shaped district, lying immediately behind the
crest of the Allegheny mountain, and at a general elevation of 2000
feet above tide, have a surface of the Barren coal measures, filling
the whole of the first and part of the Second Bituminous coal basins.
Along the Allegheny mountain the Lower Productive coal measures rise
eastward at an angle of 10 or 20, and several
of the coal beds are mined at numerous points; especially where the
Pennsylvania railroad crosses the mountain and descends the Conemaugh
south-westward to Johnstown, with a gradient exactly equal to the
diagonal slope of the Freeport upper coal bed; and also at the upper
end of the Bell's Gap railroad, on the waters of Clearfield creek,
flowing north. It is a noteworthy fact that the crest of the Allegheny
mountain in this part of its course is half made up of knobs of Mahoning
sandstone, separated by outlooking intervals of coal measures, and
fronted by a considerable lower bluff of the Pottsville conglomerate
XII, under which runs the outcrop of Mauch Chunk red shale XI, reduced
in thickness to 200 feet. Laurel hill, separating the two great coal
basins, is about as high as the Allegheny Mountain, and runs nearly
parallel with it, at a distance of 18 miles in the south and 15 in
the north. Its broad crest is made of conglomerate half across the
county; the other (northern) half, coal measures cap the mountain;
and, near the Clearfield county line, Barren measures. The dip from
the anticlinal eastward into the 1st basin is at most 10o,
and westward into the 2d basin somewhat more, but both dips rapidly
flatten upwards and downwards. The 1st basin is subdivided into two
by the Viaduct anticlinal, the axis of which, running 5 miles distant
from that of Laurel hill, rises into Somerset county, and declines
and flattens northward on Chest creek waters. The narrow wall of Mauch
Chunk red shale No. XI cut through by the railroad (here 1456' A.T.)
with the river on the west side of it 80 feet deeper than on the east
side of it, -the verticle cliffs and fallen masses of beautifully
falsebedded Pocono sandstone No. X, -and the three-mile circle which
the river has made, make this spot remarkable. After crossing the
second sub-basin, and receiving Stoney creek from the south at Johnstown,
the Conemaugh cuts through Laurel Hill, exposing arches of Pocono
(X), Mauch Chunk (XI), and Pottsville (XII) in a fine arch of vertical
cliffs, projecting from precipitous slopes 1200 feet high above the
river, which is here 1100' A.T. Nine miles further north Laurel Hill
is gapped by Black Lick Creek in a similar manner, but only deep enough
to show XI on the crest of the arch. The Siliceous limestone at the
contact of X and XI in the gap of the Conemaugh is nearly 50 feet
thick, and in spite of its flinty appearance burns and slakes well,
and makes a snow-white mortar which needs no sand. The Cambria Iron
Works at Johnstown are among the largest in the world; mining, coking
and roasting their own coal and ore on the spot, but also importing
Lake Superior red hematite, and Juniata Valley brown-hemaite and fossil
ores in large quantities for mixture. The elaborate vertical section
of the measures at Johnstown, made by Mr. John Fulton, shows the Johnston
ore bed, 2' thick, underlying 248' of Barren measures; another ore
bed 10" thick, 22' beneath it; then, 49' lower, the Freeport Upper
coal bed (E) 3' thick; 21' lower, kidney ore 10" thick; 33' lower,
coal bed D 2' 6" underlaid by a limestone 3' thick; 42' lower coal
bed D 3' 6" thick, with its underlying limestone 5' thick; 80' lower
(with two small coal beds in the interval) coal bed B 6' thick; 60'
lower, coal bed A 6' 10" thick, overlying 65' of various strata belonging
to the Pottsville Conglomerate series, No. XII. Analyses show these
coals to hold from 17 to 27 p.c. of volatile matter, and 1 p.c. water;
the ash varies from 4 to 14 p.c., but commonly runs from 4 to 6 p.c.
(See Report H2.)
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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