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Geologic units in Blair county, Pennsylvania

Wills Creek Formation through Mifflintown Formation, undivided (Silurian) at surface, covers 0.5 % of this area
Wills Creek Formation through Mifflintown Formation, undivided - Includes, in descending order, the Wills Creek Formation (Swc) and Bloomsburg and Mifflintown Formations, undivided (Sbm).
Lithology: shale; siltstone; sandstone; limestone; mudstone; dolostone (dolomite)
Wills Creek Formation (Silurian) at surface, covers 2 % of this area
Wills Creek Formation - Variegated gray, grayish-red, yellowish-gray and greenish-gray, interbedded calcareous shale, siltstone, shaly limestone, and dolomite; passes into Bloomsburg Formation in the southeast; not present east of Harrisburg.
Lithology: shale; siltstone; limestone; dolostone (dolomite)
Tuscarora Formation (Silurian) at surface, covers 5 % of this area
Tuscarora Formation - Light- to medium-gray quartzite and quartzitic sandstone and minor interbedded shale and siltstone, locally conglomeratic in lower part; includes (to the northwest) interbedded red and non-red sandstone (Castanea Member) at top; east of Harrisburg, equivalent to Minsi and Weiders Members of Shawangunk Formation.
Lithology: quartzite; sandstone; shale; siltstone; conglomerate
Clinton Group (Silurian) at surface, covers 5 % of this area
Clinton Group - Predominantly Rose Hill Formation--light-olive-gray to brownish-gray, fossiliferous shale; locally, limestone occurs near top; includes dark-reddish-gray, very fine to coarse-grained, ferruginous sandstone; east of Harrisburg, equivalent to Lizard Creek Member of Shawangunk Formation. Above Rose Hill is Keefer Formation--light- to dark-gray, fossiliferous sandstone, hematitic, oolitic sandstone, and shale; not recognized east of Harrisburg.
Lithology: shale; sandstone; limestone
Bloomsburg and Mifflintown Formations, undivided (Silurian) at surface, covers 2 % of this area
Bloomsburg and Mifflintown Formations, undivided - Includes, in descending order, the Bloomsburg Formation (Sb) and the Mifflintown Formation--interbedded dark-gray shale and medium-gray fossiliferous limestone; equivalent to "McKenzie" and "Rochester" of earlier workers; not present east of Harrisburg.
Lithology: shale; siltstone; sandstone; limestone; mudstone
Pottsville Formation (Pennsylvanian) at surface, covers 0.3 % of this area
Pottsville Formation - Predominantly gray sandstone and conglomerate; also contains thin beds of shale, claystone, limestone, and coal; includes Olean and Sharon conglomerates of northwestern Pennsylvania; thin marine limestones present in Beaver, Lawrence, and Mercer Counties; minable coals and commercially valuable high-alumina clays present locally.
Lithology: sandstone; conglomerate; shale; siltstone; claystone; limestone; coal
Glenshaw Formation (Pennsylvanian) at surface, covers < 0.1 % of this area
Glenshaw Formation - Cyclic sequences of shale, sandstone, red beds, and thin limestone and coal; includes four marine limestone or shale horizons; red beds are involved in landslides; base is at top of Upper Freeport coal.
Lithology: shale; sandstone; limestone; clastic; coal
Allegheny Formation (Pennsylvanian) at surface, covers 2 % of this area
Allegheny Formation - Cyclic sequences of sandstone, shale, limestone, clay, and coal; includes valuable clay deposits and Vanport Limestone; commercially valuable Freeport, Kittanning, and Brookville-Clarion coals present; base is at bottom of Brookville-Clarion coal.
Lithology: sandstone; shale; limestone; clay or mud; coal
Reedsville Formation (Ordovician) at surface, covers 4 % of this area
Reedsville Formation - Olive-gray to dark-gray shale, siltstone, and fine-grained, thin-bedded sandstone having graded bedding; upper sandstone is very fossiliferous; includes Antes Formation (black calcareous shale) at base along Nittany Arch.
Lithology: shale; siltstone; sandstone; black shale
Nittany and Stonehenge/Larke Formations, undivided (Ordovician) at surface, covers 3 % of this area
Nittany and Stonehenge/Larke Formations, undivided - Includes, in descending order, the Nittany (On) and Stonehenge/Larke (Osl) Formations.
Lithology: dolostone (dolomite); limestone; chert; conglomerate
Juniata Formation (Ordovician) at surface, covers 3 % of this area
Juniata Formation - Grayish-red, very fine to medium-grained, crossbedded sandstone, and grayish-red siltstone and shale; merges with underlying Bald Eagle Formation to the south; not present east of Susquehanna River, except at Spitzenberg Hill area (Berks County).
Lithology: sandstone; shale; siltstone
Coburn Formation through Loysburg Formation, undivided (Ordovician) at surface, covers 4 % of this area
Coburn Formation through Loysburg Formation, undivided - Includes, in descending order, the Coburn Formation through Nealmont Formation, undivided (Ocn) and Benner Formation through Loysburg Formation, undivided (Obl).
Lithology: limestone; shale; dolostone (dolomite); calcarenite; metavolcanic rock
Bald Eagle Formation (Ordovician) at surface, covers 2 % of this area
Bald Eagle Formation - Gray to olive-gray and grayish-red, fine- to coarse-grained, crossbedded sandstone, siltstone, and shale; some conglomerate (Lost Run Member); not present east of Susquehanna River, except at Spitzenberg Hill area (Berks County).
Lithology: sandstone; siltstone; shale; conglomerate
Bellefonte and Axemann Formations, undivided (Ordovician) at surface, covers 7 % of this area
Bellefonte and Axemann Formations, undivided - Includes, in descending order, the Bellefonte (Obf) and Axemann (Oa) Formations.
Lithology: dolostone (dolomite); limestone; sandstone
Mauch Chunk Formation (Mississippian) at surface, covers 2 % of this area
Mauch Chunk Formation - Grayish-red shale, siltstone, sandstone, and some conglomerate; some local nonred zones. Includes Loyalhanna Member (crossbedded, sandy limestone) at base in south-central and southwestern Pennsylvania; also includes Greenbrier Limestone Member, and Wymps Gap and Deer Valley Limestones, which are tongues of the Greenbrier. Along Allegheny Front from Blair County to Sullivan County, Loyalhanna Member is greenish-gray, calcareous, crossbedded sandstone.
Lithology: shale; siltstone; sandstone; conglomerate; limestone
Rockwell Formation (Mississippian and Devonian) at surface, covers 1 % of this area
Rockwell Formation - Buff, fine- to medium-grained, crossbedded, argillaceous sandstone and dark-gray shale; includes some carbonaceous shale, sporadic conglomerate beds, and diamictite; included in lower "Pocono" of earlier workers.
Lithology: sandstone; shale; conglomerate
Burgoon Sandstone (Mississippian) at surface, covers 2 % of this area
Burgoon Sandstone - Buff, medium-grained, crossbedded sandstone; includes shale and coal; in places, contains conglomerate at base; contains plant fossils; equivalent to Pocono Formation of Ridge and Valley province.
Lithology: sandstone; conglomerate; shale; coal
Keyser and Tonoloway Formations, undivided (Devonian and Silurian) at surface, covers 4 % of this area
Keyser and Tonoloway Formations, undivided - In descending order: Keyser Formation--medium-gray, crystalline to nodular, fossiliferous limestone; upper part laminated and mud-cracked; not present east of Harrisburg; passes into lower Coeymans, Rondout, and Decker Formations in the east. Tonoloway Formation--medium-gray, laminated, mud-cracked limestone containing some medium-dark- or olive-gray shale interbeds; lower part passes into Wills Creek Formation east and south; passes into Bossardville and Poxono Island beds in the east.
Lithology: limestone; shale
Keyser Formation through Mifflintown Formation, undivided (Devonian and Silurian) at surface, covers 0.4 % of this area
Keyser Formation through Mifflintown Formation, undivided - In descending order: Keyser Formation--limestone; Tonoloway Formation--limestone and interbedded shale; Wills Creek Formation--interbedded shale, siltstone, limestone, and dolomite; Bloomsburg Formation--grayish-red and greenish-gray shale, siltstone, sandstone, and mudstone; Mifflintown Formation--interbedded shale and limestone.
Lithology: limestone; shale; siltstone; sandstone; mudstone; dolostone (dolomite)
Scherr Formation (Devonian) at surface, covers 2 % of this area
Scherr Formation - Chiefly siltstone; some fine-grained sandstone, shale, and mudstone; light olive gray; marine fossils.
Lithology: siltstone; sandstone; shale; mudstone
Onondaga and Old Port Formations, undivided (Devonian) at surface, covers 2 % of this area
Onondaga and Old Port Formations, undivided - Includes, in descending order, the Onondaga Formation (Don), Ridgeley Member of Old Port Formation (Dor), and Shriver, Mandata, Corriganville, and New Creek Members of Old Port Formation, undivided (Dosn).
Lithology: shale; sandstone; limestone; chert; shale; siltstone; bentonite
Lock Haven Formation (Devonian) at surface, covers 3 % of this area
Lock Haven Formation - Interbedded olive-gray mudstone, siltstone, sandstone, and thin conglomerate; marine fossils throughout; "Chemung" of earlier workers. Laterally equivalent to Scherr and Foreknobs Formations.
Lithology: mudstone; siltstone; sandstone; conglomerate
Hamilton Group (Devonian) at surface, covers 4 % of this area
Hamilton Group - Includes, in descending order, the Mahantango (Dmh) and Marcellus (Dmr) Formations.
Lithology: black shale; shale; siltstone; limestone; sandstone; bentonite
Foreknobs Formation (Devonian) at surface, covers 2 % of this area
Foreknobs Formation - Interbedded sandstone, siltstone, and shale; gray to olive gray, red near top; substantial brownish-gray sandstone; some marine fossils; a few conglomerate beds at base and top.
Lithology: sandstone; siltstone; shale; conglomerate
Sherman Creek Member of Catskill Formation (Devonian) at surface, covers 3 % of this area
Sherman Creek Member of Catskill Formation - Alternating grayish-red mudstone and siltstone in poorly defined fining-upward cycles, and minor intervals of gray sandstone; laterally equivalent to Berry Run, Sawmill Run, Packerton, and Long Run Members of eastern Pennsylvania.
Lithology: mudstone; siltstone; sandstone
Catskill Formation (Devonian) at surface, covers 7 % of this area
Catskill Formation - Grayish-red sandstone, siltstone, shale, and mudstone; locally conglomeratic; contains gray sandstone in upper part; lithologies arranged in fining-upward cycles; equivalent to the Hampshire Formation south of Pennsylvania.
Lithology: sandstone; siltstone; shale; mudstone; conglomerate
Irish Valley Member of Catskill Formation (Devonian) at surface, covers 0.5 % of this area
Irish Valley Member of Catskill Formation - Nonmarine, grayish-red siltstone and mudstone, and gray and grayish-red sandstone interbedded with minor, thin, light-olive-gray marine siltstone; arranged in fining-upward cycles. Lower part of member has conglomeratic sandstones.
Lithology: siltstone; mudstone; sandstone; conglomerate
Duncannon Member of Catskill Formation (Devonian) at surface, covers 1 % of this area
Duncannon Member of Catskill Formation - Grayish-red sandstone, siltstone, and mudstone in fining-upward cycles; conglomerate occurs at base of some cycles.
Lithology: sandstone; siltstone; mudstone; conglomerate
Brallier and Harrell Formations, undivided (Devonian) at surface, covers 9 % of this area
Brallier and Harrell Formations, undivided - In descending order: Brallier--medium-gray, planar-bedded siltstone interbedded with light-olive shale; sparse marine fauna; Harrell--black shale (Burket Member) and dark-gray shale.
Lithology: siltstone; shale; black shale
Waynesboro Formation (Cambrian) at surface, covers < 0.1 % of this area
Waynesboro Formation - Greenish-gray and grayish-purple shale interbedded with greenish-gray sandstone and conglomerate; occurs in Henrietta fault block only.
Lithology: shale; sandstone; conglomerate
Warrior Formation (Cambrian) at surface, covers 0.4 % of this area
Warrior Formation - Gray, thin- to medium-bedded, fossiliferous, cyclic limestone bearing stromatolites; interbedded with thick-bedded crystalline dolomite and some sandstone.
Lithology: limestone; dolostone (dolomite); sandstone
Pleasant Hill Formation (Cambrian) at surface, covers < 0.1 % of this area
Pleasant Hill Formation - Gray, thin-bedded, argillaceous limestone interbedded with shale, siltstone, and sandstone.
Lithology: limestone; shale; siltstone; sandstone
Gatesburg Formation (Cambrian) at surface, covers 4 % of this area
Gatesburg Formation - Gray dolomite, limestone, and sandstone. Includes the Mines Member (CAgm) and four lower members (CAgl).
Lithology: dolostone (dolomite); limestone; sandstone; chert

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