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Description of the Geology of
Centre County

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Centre. - Area, 1230 square miles; population in 1880, 37,922. This large and important county presents all the most interesting features of the Palaeozoic geology of the State on a grand scale- a wide expanse of mountain upland, with important coal areas on its top, in the western townships- an uninterrupted Devonian and Silurian valley crossing its middle townships- great anticlinal waves bringing up to the present surface hundreds of square miles of Siluro-Cambrian magnesian limestones, charged with superb deposits of brown hematite iron ore-long parallel symmetrical synclinal ranges of Medina-Oneida mountains separating the limestone valleys- and a labyrinth of these mountains in the south-eastern townships, formed by numerous close rock-waves and faulted in several places. Most of the Allegheny mountain plateau has been denuded of its former covering of coal measures; but considerable minable areas of them are preserved along the center line of the First Bituminous basin, viz: a continuous belt 2 or 3 miles wide and 16 miles long, along the Moshannon river in Rush township; another 3 miles wide by 9 miles long, around Snowshoe, Moshannon, Pine Glen, and Germania, stretching west to the Susquehanna river; and seventeen other smaller patches along the headwaters of Beech creek, and on Hays run, along the Burnside-Snowshoe township line, and in Curtain township. The Snowshoe coal beds, first mined in the early part of the century, are now extensively worked. The Freeport upper coal, 5' thick, caps the highest knobs, Askey hill, &c., covered with the last remaining blocks of the great Mahoning sandstone. The Freeport lower coal, so important at Karthaus, is thin in Centre County. The Kittanning upper coal is the bed of the region, from 5 to 7 feet thick, in three benches, with a coarse cannel roof. Numerous small downthrow faults are met in the mines. Analyses show 70 per cent carbon, 25 gas, 3 ash, 1 sulphur, less than 1 water, and good coke is made of it. Four other beds, 3' or 4' thick, exist; and several limestone beds, one if which, the Freeport lower limestone, is the key-rock of the district, from which all measurements are made and the coal beds are identified. The Pottsville conglomerate, XII, 250' thick, makes the crest of the Allegheny mountain * and the rocky sides innumerable ravines. Under it the Mauch Chunk red shale, XI, 150' thick, appears; and is also brought up in the bed of the Susquehanna, below Salt Lick, at the west end of Burnside township, and along both sides of Beech Creek valley, in Curtin township, everywhere topped by a plate of carbonate of iron, "the red ore bed," of variable thickness, never exceeding 4'. The Pocono sandstone, X, is more than 600' thick, and forms a bold, straight, forest-covered ridge of coarse, and often conglomerate white sandstone, covered with bowlders, and keeping a pretty regular height of 2200' A.T. The Catskill rocks, IX, form a broad, flat terrace in front of the Allegheny mountain its whole length, which can be well studied in Worth township, where the old turnpike to Philipsburg runs along it; they are 2600' thick. The Chemung and Hamilton formations form the foot hills, and the Marcellus dark shales (800') the bottom of the Bald Eagle valley; in all more than 6000' thick of middle and lower Devonian measures, rising from beneath the Coal regions at increasing angles from 100 to 600. The astonishing straightness of the Bald Eagle valley (N. 450 E.) across the county is explained by the vertical attitude of the rocks of the Bald Eagle mountain, at the west foot of which runs the low ridge of Oriskany sandstone VII, and Lower Helderberg limestone VI. At the Clinton county line VII is 130' thick, but thins southward to nothing a few miles south of Milesburg, and has been seen after that at only one place; it furnishes inexhaustible quantities of the finest glass sand, is excessively fossiliferous, but seems to offer no iron ore. The limestone VI is finely developed in Centre County, 1020' thick, and has been quarried in the neighborhood of the charcoal iron furnaces. It is both argillaceous and cherty, and, as usual, quite fossiliferous. No. V (Onondaga and Clinton) 1040' thick, makes the west slope of Bald Eagle Mountain, but its fossil ore beds are scarcely recognizable; one thin layer was formerly mined a little at Howard. "Paint Springs" issue from its outcrop. The Bald Eagle mountain rocks stand vertical; the west crest made by Medina white sandstone (938',) the east crest by Oneida white sandstone (710',) and the interval by Medina red rocks (774',) in all 2425 feet thick, containing neither useful minerals nor any fossils, except a few casts of a sea weed called Arthrophycus harlani. This triple formation (IV) makes all the other mountains of the county: Nittany, Brush, Penns, Tussey, and Seven mountains; but as their dips are not vertical, their crests are made by the upper (Medina) division, while bold and beautiful terraces are made by the lower (Oneida), cut into short lengths by innumerable ravines heading in the softer outcrops of the middle division. No.III, Loraine (Hudson River) and Utica slates, 1000' thick, make the foot slope of the terrace, and in front of it spreads the fertile but waterless rolling plain of the great valley limestone formation No. II (at least 6000' thick) the bottom of which is nowhere to be seen. Innumerable caverns lie concealed, through which flow streams, fed through sink-holes in the surface. One of these caverns is the channel-way for a considerable stream which sinks in Brush valley and rises in a great spring in Nittany valley, passing beneath Nittany Mountain at a depth of at least 4000 feet. Another sinks into a cave near the end of Brush Mountain, and rises in the "Fathomless spring" as Penn's creek. Big Hollow, along which the Bellefonte and Buffalo Run railroad runs, is the floor of an ancient cavern five miles long, the roof of which has been long since carried away, and sink holes along its course show that a new cavern has been found beneath it. Caverns filled with iron ore, on Sinking creek near Egg Hill in Potter Township, prove that the great brown hematite pipe ore deposits of Centre county fill depressions in the limestone which were once roofed like other caverns. Of these immense ore beds the largest and most famous is that of Pennsylvania furnace, in the southern corner of the county, the open excavations extending 1500 feet in length by 500' wide and 60' deep, the ore being known to be 30' or 40' deeper. Seven groups of these deposits, embracing more than fifty banks, are described by Mr. d' Invilliers, in Report T4.

* 2236' A.T. at middle summit; 2281' northern summit Three Springs at head of Moshannon; 2614' highest ground one mile further east; 2043 at railroad grade at Emig's gap; 1735' in the notch where the Snowshoe R.R. crosses it; level of Snowshoe 1572'.

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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