Hamilton Group (including Mahantango Formation and Marcellus Shale), and including Tioga Metabentontite Bed, and Needmore Shale (MDDhn;1)

Hamilton Group including Mahantango Formation - Dark gray, laminated shale, siltstone, and very fine-grained sandstone; thickness 600 feet in west, increases to 1,200 feet in east, and Marcellus Shale - Gray-black, thinly laminated, pyritic, carbonaceous shale; thickness 250 feet in east, increases to 500 feet in west. Also includes Tioga Metabentonite Bed - Brownish-gray, thinly laminated shale containing sand-size mica flakes; thickness less than one foot; and Needmore Shale - Olive-gray to black shale and dark, thin-bedded, fossiliferous, argillaceous limestone; thickness ranges from 70 to 145 feet.

State	Maryland
Name	Hamilton Group (including Mahantango Formation and Marcellus Shale), and including Tioga Metabentontite Bed, and Needmore Shale
Geologic age	Devonian
Original map label	Dhn
Comments	Hamilton Group, Tioga Metabentonite Bed, and Needmore Shale formerly were designated as Romney Formation.
Primary rock type	shale
Secondary rock type	siltstone
Other rock types	sandstone; black shale; limestone
Lithologic constituents	Major Sedimentary > Clastic > Mudstone > ShaleHamilton Group including Mahantango Formation - Dark gray, laminated shale, siltstone, and very fine-grained sandstone; thickness 600 feet in west, increases to 1,200 feet in east, and Marcellus Shale - Gray-black, thinly laminated, pyritic, carbonaceous shale; thickness 250 feet in east, increases to 500 feet in west. Needmore Shale - Olive-gray to black shale and dark, thin-bedded, fossiliferous, argillaceous limestone; thickness ranges from 70 to 145 feet. Minor Sedimentary > Clastic > Sandstone Sedimentary > Clastic > Siltstone Sedimentary > Clastic > Mudstone > Shale > Black-shaleHamilton Group including Mahantango Formation - Dark gray, laminated shale, siltstone, and very fine-grained sandstone; thickness 600 feet in west, increases to 1,200 feet in east, and Marcellus Shale - Gray-black, thinly laminated, pyritic, carbonaceous shale; thickness 250 feet in east, increases to 500 feet in west. Also includes Tioga Metabentonite Bed - Brownish-gray, thinly laminated shale containing sand-size mica flakes; thickness less than one foot; and Needmore Shale - Olive-gray to black shale and dark, thin-bedded, fossiliferous, argillaceous limestone; thickness ranges from 70 to 145 feet. Incidental Sedimentary > Carbonate > Limestone
Map references	Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.
Unit references	Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000. Unpublished digital version of the Maryland state geologic map that was digitized by the USGS Water Resources Office in Towson, MD
Geographic coverage	Allegany - Washington