Description of the Geology of
Armstrong County
Pennsylvania

 
Armstrong.- Area, 610 square miles; population in 1880, 47,641. The whole surface is sculptured in all directions by the erosion of the Barren Measures, lying almost horizontally, although several wide and gentle rolls traverse it from northeast to southwest, bringing the Lower Productive coal measures above water level along the Allegheny river and its great branches from the east, the Kiskiminitas, Crooked, Cowanshannock, Pine, Mahoning, and Redbank creeks; and on the western side, along Buffalo creek, Glade run, and other small streams descending from Butler county. The Pittsburgh coal bed occupies only a short and narrow basin in the southeast corner of the county. The Barren measures are 600 feet thick, including the Mahoning Sandstone at the bottom, the long horizontal outcrops of which edge all the valleys of the county with cliffs, and rough their steep slopes with fallen rocks. Two coal beds, each with a limestone bed beneath it, are mined near water level at Freeport, and rise slowly northward until they merely cap the highest hills. The three next coals are mined at Kittanning, the highest one having a limestone bed under it, and the lowest one, overlying the Ferriferous Limestone, which appears at the surface in southern Armstrong only where Crooked creek is crossed by the Paddy's Run axis. It has isolated outcrops from 3 to 5 miles long at Greendale on Cowanshannock; on both forks of Pine creek from Echo to Pine P.O., and near Goheenville; and an unbroken outcrop along both sides of the Allegheny river and Mahoning and Redbank creeks from Kittanning northward. It varies from 4 to 18 feet in thickness, and carries the famous " buhrstone " brown hematite iron-ore on which ran in early years the old Rock, Bear Creek, Allegheny, Buffalo, Ore Hill, Cowanshannock, Mahoning, America, Phoenix, Pine Creek, Olney, Stewardson, Monticello, and Great Western cold-blast charcoal furnaces (with their forges and rolling mills,) some of which were changes to hot-blast coke furnaces. The two Clarion coal beds (beneath the limestone) only appear above water level in the northern townships; and the Pottsville Conglomerate No. XII shows its upper massive layers where the anticlinal lines cross the principal river valleys; but nearly the whole formation (300 feet thick) has been cut through by the river at Parker City, where the Clarion oil belt crosses the valley. Here on the flat beneath its vertical cliffs and on the terraces above, hundreds of derricks once stood, thick as trees in a forest, draining the Third Oil Sand from a depth of 800 feet beneath the river. At Brady's Bend this third oil sand lies 1,000 feet beneath the river. In all other parts of this county the wells, some of them 2,000 feet deep, have yielded no petroleum. (See Report H⁵.)

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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