The upper Devonian rocks of southwest Pennsylvania

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ID: 306981
1878
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Abstract
THE Vespertine or Pocono sandstone of the Pennsylvania Survey is a massive sandstone from 350 to 450 feet thick in southwestern Pennsylvania, and is the lower division of the Lower Carboniferous rocks.In Fayette and Westmoreland Counties, under Laurel and Chestnut Ridges, the last of the Alleghany Ridges toward the west, the Vespertine sandstone rests immediately upon a mass of gray to reddish-gray sandstones, interstratified with red to gray and olive shales.These, representing the upper portion of the Devonian, are well exposed in the gaps of the Conemaugh River through the two ridges, af:; well as in the similar gaps made by the Y oughiogheny River.In Laurel Ridge there are a few imperfect exposures in the deeper gorges made by the larger streams within Westmoreland and nnrthern Fayette.In Chestnut Ridge there are no exposures of the Devonian in Westmoreland County, but in Fayette, south from the Youghiogheny River, these rocks are shown in the gap made by Dunbar Creek, as well as on the National Road, and in the deep gorges made by Shute's Run, Redstone Creek and the principal tributaries to Sandy Creek.Lithologically, the transition from the Vespertine or Pocono sandstone to the Devonian rocks is sufficiently distinct.The great sandstone breaks down into a sandy shale, interstratified with some argillaceous shale, which in turn becomes merged into the well-defined red-gray to olive shales and sandstones representing the Upper Devonian.During the hasty examillation of 1876, I was unable to make any close study of the section, and so provisionally regarded the lower rocks as belonging to the same series with the upper.This conclusion was given in my report to Professor Lesley for 1876.But the examinations made in the several gaps during 1877 showed the previous conclusion to be erroneous, and that the lower portion of the section from the very base of the Pocono sandstone is Devonian and not Lower Carboniferous.L~ general section of the Devonian rocks, as observed in the gaps mentioned above, is as follows:-
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Authors John J. Stevenson
Journal american journal of science
Year 1878
DOI
10.2475/ajs.s3-15.90.423
URL
https://doi.org/10.2475/ajs.s3-15.90.423
Keywords Keywords not found

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