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Mineral Resources > Online Spatial Data > Geology > by state > Pennsylvania Geology

Geologic units in Franklin county, Pennsylvania

Hamilton Group (Devonian) at surface, covers 0.6 % of this area

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

Lithology: black shale; shale; siltstone; limestone; sandstone; bentonite

St. Paul Group (Ordovician) at surface, covers 7 % of this area

St. Paul Group - Very finely crystalline, "birdseye" limestone at top and base, granular fossiliferous limestone, black chert, and dolomite in middle.

Lithology: limestone; chert; dolostone (dolomite)

Reedsville Formation (Ordovician) at surface, covers < 0.1 % 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

Clinton Group (Silurian) at surface, covers 4 % 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

Elbrook Formation (Cambrian) at surface, covers 6 % of this area

Elbrook Formation - Microcrystalline limestone and, in places, marble; includes subordinate dolomite containing abundant phyllitic layers; occurs in Chester and Montgomery Counties; relation to Elbrook of Cumberland Valley sequence is uncertain.

Lithology: limestone; dolostone (dolomite); phyllite; marble

Metabasalt (Precambrian) at surface, covers 0.3 % of this area

Metabasalt - Dark-gray, fine-grained intrusives; locally, mineralogy is altered and unit has greenish color.

Lithology: meta-basalt

Pinesburg Station Formation (Ordovician) at surface, covers 2 % of this area

Pinesburg Station Formation - Light-colored, thick-bedded, finely laminated dolomite; some limestone.

Lithology: dolostone (dolomite); limestone

Juniata and Bald Eagle Formations, undivided (Ordovician) at surface, covers 4 % of this area

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

Lithology: sandstone; siltstone; shale; conglomerate

Martinsburg Formation (Ordovician) at surface, covers 34 % of this area

Martinsburg Formation - Gray to dark-gray, buff-weathering shale.

Lithology: shale

Shadygrove Formation (Cambrian) at surface, covers 0.9 % of this area

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

Lithology: limestone; chert

Brallier and Harrell Formations, undivided (Devonian) at surface, covers < 0.1 % 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 2 % 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

Wills Creek Formation (Silurian) at surface, covers 0.6 % 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)

Montalto Member of Harpers Formation (Cambrian) at surface, covers 3 % of this area

Montalto Member of Harpers Formation - Gray quartzite.

Lithology: quartzite

Tomstown Formation (Cambrian) at surface, covers 3 % of this area

Tomstown Formation - Massive dolomite containing thin shaly interbeds.

Lithology: dolostone (dolomite); shale

Onondaga and Old Port Formations, undivided (Devonian) at surface, covers 0.3 % 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).

Lithology: shale; sandstone; limestone; chert; shale; siltstone; bentonite

Keyser Formation through Mifflintown Formation, undivided (Devonian and Silurian) at surface, covers < 0.1 % 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)

Rockdale Run Formation (Ordovician) at surface, covers 7 % of this area

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

Lithology: limestone; dolostone (dolomite); chert

Tuscarora Formation (Silurian) at surface, covers 4 % 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

Harpers Formation (Cambrian) at surface, covers 0.9 % of this area

Harpers Formation - Dark-greenish-gray phyllite and schist containing thin quartzite layers.

Lithology: phyllite; schist; quartzite

Graywacke and shale of Martinsburg Formation (Ordovician) at surface, covers 3 % of this area

Graywacke and shale of Martinsburg Formation - Abundant impure sandstone (graywacke) interbeds.

Lithology: graywacke

Weverton and Loudoun Formations, undivided (Cambrian) at surface, covers 2 % of this area

Weverton and Loudoun Formations, undivided - In descending order: Weverton--gray to purplish-gray quartzite and quartzose conglomerate containing rounded pebbles. Loudoun--sericitic slate and purplish-gray, crumbly, poorly sorted, arkosic sandstone and conglomerate.

Lithology: quartzite; slate; conglomerate; arkose

Metarhyolite (Precambrian) at surface, covers 1 % of this area

Metarhyolite - Light gray, green, and purple; commonly schistose, containing quartz augen and veins.

Lithology: meta-rhyolite

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

Zullinger Formation - Interbanded and interlaminated limestone and dolomite, thin- to thick-bedded; stromatolitic limestone; several thin, local quartz sandstone beds.

Lithology: limestone; dolostone (dolomite); sandstone

Antietam Formation (Cambrian) at surface, covers 1 % of this area

Antietam Formation - Gray, buff-weathering quartzite and quartz schist.

Lithology: quartzite; schist

Bellefonte Formation (Ordovician) at surface, covers 2 % of this area

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

Lithology: dolostone (dolomite); sandstone

Stonehenge Formation (Ordovician) at surface, covers 2 % of this area

Stonehenge Formation - Stromatolitic, fine-grained limestone; includes coarser grained and conglomeratic, siliceous, laminated Stoufferstown Formation at base in most of Cumberland Valley.

Lithology: 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

Keyser and Tonoloway Formations, undivided (Devonian and Silurian) at surface, covers 0.5 % 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

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

Chambersburg Formation - Dark-gray, cobbly, argillaceous limestone; abundant irregular shale partings; some metabentonite beds present.

Lithology: limestone; shale; metavolcanic rock

Greenstone schist (Precambrian) at surface, covers < 0.1 % of this area

Greenstone schist - Fine to medium grained, light to medium green; includes probable metavolcanic rocks.

Lithology: schist; metavolcanic rock