Geologic units in Fulton county, Pennsylvania

Catskill Formation (Devonian) at surface, covers 29 % of this area

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.

Pocono Formation (Mississippian) at surface, covers 10 % of this area

Light-gray to buff or light-olive-gray, medium-grained, crossbedded sandstone and minor siltstone; commonly conglomeratic at base and in middle; medial conglomerate, where present, is used to divide into Mount Carbon and Beckville Members; equivalent to Burgoon Sandstone of Allegheny Plateau.

Brallier and Harrell Formations, undivided (Devonian) at surface, covers 9 % of this area

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.

Hamilton Group (Devonian) at surface, covers 7 % of this area

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

Foreknobs Formation (Devonian) at surface, covers 7 % of this area

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 6 % of this area

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.

Scherr Formation (Devonian) at surface, covers 4 % of this area

Chiefly siltstone; some fine-grained sandstone, shale, and mudstone; light olive gray; marine fossils.

Reedsville Formation (Ordovician) at surface, covers 3 % of this area

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.

Rockwell Formation (Mississippian and Devonian) at surface, covers 3 % of this area

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.

Irish Valley Member of Catskill Formation (Devonian) at surface, covers 2 % of this area

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.

Clinton Group (Silurian) at surface, covers 2 % of this area

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.

Tuscarora Formation (Silurian) at surface, covers 2 % of this area

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.

Nittany and Stonehenge/Larke Formations, undivided (Ordovician) at surface, covers 2 % of this area

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

Wills Creek Formation (Silurian) at surface, covers 2 % of this area

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.

Coburn Formation through Loysburg Formation, undivided (Ordovician) at surface, covers 2 % of this area

Includes, in descending order, the Coburn Formation through Nealmont Formation, undivided (Ocn) and Benner Formation through Loysburg Formation, undivided (Obl).

Onondaga and Old Port Formations, undivided (Devonian) at surface, covers 2 % of this area

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).

Juniata and Bald Eagle Formations, undivided (Ordovician) at surface, covers 1 % of this area

Includes, in descending order, the Juniata (Oj) and Bald Eagle (Obe) Formations.

Bellefonte Formation (Ordovician) at surface, covers 1 % of this area

Medium-gray, brownish-weathering, medium-bedded dolomite and minor sandstone; very fine grained Tea Creek Member above, and crystalline Coffee Run Member below.

Keyser and Tonoloway Formations, undivided (Devonian and Silurian) at surface, covers 1 % of this area

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.

Pottsville Formation (Pennsylvanian) at surface, covers 1.0 % of this area

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.

Bloomsburg and Mifflintown Formations, undivided (Silurian) at surface, covers 0.9 % of this area

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.

Keyser Formation through Mifflintown Formation, undivided (Devonian and Silurian) at surface, covers 0.6 % of this area

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.

Allegheny Formation (Pennsylvanian) at surface, covers 0.4 % of this area

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.

Burgoon Sandstone (Mississippian) at surface, covers 0.4 % of this area

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.

Rockdale Run Formation (Ordovician) at surface, covers 0.3 % of this area

Mostly limestone; some dolomite interbeds; some chert near middle and top; stromatolitic limestone in middle; pinkish marbleoid limestone and chert at base.

Shadygrove Formation (Cambrian) at surface, covers 0.3 % of this area

Pure, light-colored limestone, stromatolitic in part; abundant pinkish limestone and cream-colored chert.

Keyser Formation through Clinton Group, undivided (Devonian and Silurian) at surface, covers 0.1 % of this area

Same as Keyser-through-Mifflintown (DSkm) interval, plus Clinton Group at base. Clinton includes the following, in descending order: Keefer Formation--fossiliferous sandstone and hematitic, oolitic sandstone and shale; Rose Hill Formation--fossiliferous shale.

Nittany Formation (Ordovician) at surface, covers < 0.1 % of this area

Medium- to dark-gray, thick-bedded dolomite containing chert and siliceous oolites.

Hampshire Formation (Devonian) at surface, covers < 0.1 % of this area

Interbedded red shale, red mudstone, and red to brown cross-bedded siltstone and sandstone; some thin green shale; greenish-gray sandstone and shale toward top; fragmentary plant fossils; thickness 1,400 to 2,000 feet in west, increases to 3,800 feet in east.

"Chemung" Formation, Parkhead Sandstone, Brallier Formation, and Harrell Shale (Devonian) at surface, covers < 0.1 % of this area

"Chemung" Formation - Predominantly marine beds characterized by gray to olive-green graywacke, siltstone, and shale; thickened ranges from 2,000 to 3,000 feet; Parkhead Sandstone - Gray to olive-green sandy shale, conglomeratic sandstone and graywacke; present in Washington County, identification uncertain in west; thickness averages 400 feet; Brallier Fomation - (Woodmont Shale of earlier reports). Medium to dark gray, laminated shale and siltstone; weathers to light olive-gray; grain size coarsens upward; thickness about 2,000 feet in west, about 1,7000 feet in east; and Harrell Shale - Dark gray laminated shale; absent in east where Brallier lies directly on Mahantango, Tully Limestone lies near base in west, in subsurface of Garrett County; total thickness in west 140 to 300 feet.

Pocono Group, including the Purslane Sandstone and Rockwell Formation (Mississippian) at surface, covers < 0.1 % of this area

Pocono Group - Gray, white, tan, and brown, thin- to thick-bedded, cross-bedded sandstone, locally conglomeratic; interbedded gray and reddish-brown shale, mudstone, and siltstone; fragmentary plant fossils. Undifferentiated in Garrett and western Allegeny Counties. Includes Purslane Sandstone - White, thick-bedded, coarse-grained sandstone and conglomerate with thin coal beds and red shales. Eastern Allegany and Washington Counties. And also inlcudes Rockwell Formation - Coarse-grained arkosic sandstone, fine-grained conglomerate, and buff shale; dark shale with thin coal beds near base. Eastern Allegany and Washington Counties.