This is a piece of sandstone. The stone appears to have been weathered by frost action, or frost wedging. The water flowed into small fissures, and expanded when it froze, which expanded the cracks in the rock.Galleries:Allegheny Portage Railroad, Rock SpecimensKeywords:allegheny portage railroad, frost wedging, gallitzin, pennsylvania, sandstone, skew arch bridgePhoto Location: Skew Arch Bridge, Allegheny Portage Railroad National Historic Site, PennsylvaniaPhotographer: Dr. Roy WinkelmanDate of Photo: 11/25/2011Device Make: CanonDevice Model: Canon EOS 5D Mark IIOriginal Dimensions: 5616×3744Picture Orientation: LandscapeGPS Coordinates: 40°27'11.00"N 78°32'34.23"WPicture Number: 15924
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