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Geologic units in Blair county, Pennsylvania

Brallier and Harrell Formations, undivided (Devonian) at surface, covers 10 % 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.

Catskill Formation (Devonian) at surface, covers 8 % 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.

Bellefonte and Axemann Formations, undivided (Ordovician) at surface, covers 8 % of this area

Bellefonte and Axemann Formations, undivided - Includes, in descending order, the Bellefonte (Obf) and Axemann (Oa) Formations.

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

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.

Hamilton Group (Devonian) at surface, covers 5 % of this area

Hamilton Group - Includes, in descending order, the Mahantango (Dmh) and Marcellus (Dmr) Formations.

Coburn Formation through Loysburg Formation, undivided (Ordovician) at surface, covers 5 % 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).

Gatesburg Formation (Cambrian) at surface, covers 5 % of this area

Gatesburg Formation - Gray dolomite, limestone, and sandstone. Includes the Mines Member (CAgm) and four lower members (CAgl).

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

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.

Nittany and Stonehenge/Larke Formations, undivided (Ordovician) at surface, covers 4 % of this area

Nittany and Stonehenge/Larke Formations, undivided - Includes, in descending order, the Nittany (On) and Stonehenge/Larke (Osl) Formations.

Juniata Formation (Ordovician) at surface, covers 4 % 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

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.

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.

Onondaga and Old Port Formations, undivided (Devonian) at surface, covers 3 % 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).

Wills Creek Formation (Silurian) at surface, covers 3 % 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.

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.

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.

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.

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.

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.

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.

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).

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.

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.

Wills Creek Formation through Mifflintown Formation, undivided (Silurian) at surface, covers 0.6 % 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).

Irish Valley Member of Catskill Formation (Devonian) at surface, covers 0.6 % 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.

Warrior Formation (Cambrian) at surface, covers 0.5 % of this area

Warrior Formation - Gray, thin- to medium-bedded, fossiliferous, cyclic limestone bearing stromatolites; interbedded with thick-bedded crystalline dolomite and some sandstone.

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.

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.

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.

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.

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.