USGS Home
Contact USGS
Search USGS

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

Geologic units in Cumberland county, Pennsylvania

Rockdale Run Formation (Ordovician) at surface, covers 9 % 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

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

Limestone of Martinsburg Formation - Dark-gray, thin-bedded, platy argillaceous limestone containing some beds of shale.

Lithology: limestone; shale

Gettysburg conglomerate (Triassic) at surface, covers < 0.1 % of this area

Gettysburg conglomerate - Gray quartz conglomerate, sandstone, and red siltstone and mudstone.

Lithology: conglomerate; sandstone; siltstone; mudstone

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

Tomstown Formation - Massive dolomite containing thin shaly interbeds.

Lithology: dolostone (dolomite); shale

Limestone of Hamburg sequence (Ordovician) at surface, covers 0.5 % of this area

Limestone of Hamburg sequence - Conspicuous limestone.

Lithology: limestone

Montalto Member of Harpers Formation (Cambrian) at surface, covers 8 % of this area

Montalto Member of Harpers Formation - Gray quartzite.

Lithology: quartzite

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

Hershey and Myerstown Formations, undivided (Ordovician) at surface, covers < 0.1 % of this area

Hershey and Myerstown Formations, undivided - In descending order: Hershey--dark-gray to black, thin-bedded, argillaceous limestone; Myerstown--medium- to dark-gray, platy, medium-crystalline limestone; carbonaceous at base.

Lithology: limestone

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

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

Lithology: limestone; chert

Juniata and Bald Eagle Formations, undivided (Ordovician) at surface, covers 2 % 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 25 % of this area

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

Lithology: shale

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

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

Lithology: dolostone (dolomite); limestone

Clinton Group (Silurian) at surface, covers 0.6 % 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

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

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

Lithology: meta-basalt

Elbrook Formation (Cambrian) at surface, covers 7 % 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

Diabase (Jurassic) at surface, covers < 0.1 % of this area

Diabase - Medium- to coarse-grained, quartz-normative tholeiite; composed of labradorite and various pyroxenes; occurs as dikes, sheets, and a few small flows. Includes the dark-gray York Haven Diabase (high titanium oxide) and the slightly younger Rossville Diabase (low titanium oxide). In chilled margins, the Rossville is distinguished from the York Haven by its lighter gray color and distinctive, sparse, centimeter-sized calcic-plagioclase phenocrysts.

Lithology: diabase

St. Paul Group (Ordovician) at surface, covers 6 % 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)

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

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

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

Lithology: limestone; shale; metavolcanic rock

Hamburg sequence rocks (Ordovician) at surface, covers 6 % of this area

Hamburg sequence rocks - Predominantly greenish gray, gray, purple, and maroon shale, siltstone, and graywacke; includes some wildflysch having Martinsburg matrix.

Lithology: shale; siltstone; graywacke; conglomerate

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

Epler Formation - Very finely crystalline, light-gray limestone interbedded with gray dolomite; coarsely crystalline limestone lenses present.

Lithology: limestone; dolostone (dolomite)

Stonehenge Formation (Ordovician) at surface, covers 1 % 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

Antietam Formation (Cambrian) at surface, covers 1.0 % of this area

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

Lithology: quartzite; schist

Graywacke of Hamburg sequence (Ordovician) at surface, covers 0.4 % of this area

Graywacke of Hamburg sequence - Predominantly graywacke.

Lithology: graywacke

Zullinger Formation (Cambrian) at surface, covers 7 % 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

Gettysburg Formation (Triassic) at surface, covers 0.7 % of this area

Gettysburg Formation - Reddish-brown to maroon, silty mudstone and shale containing thin red sandstone interbeds; several thin beds of impure limestone.

Lithology: mudstone; silt; shale; sandstone; limestone

Metarhyolite (Precambrian) at surface, covers 4 % of this area

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

Lithology: meta-rhyolite

Weverton and Loudoun Formations, undivided (Cambrian) at surface, covers 4 % 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

Harpers Formation (Cambrian) at surface, covers 0.1 % 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 2 % of this area

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

Lithology: graywacke

Tuscarora Formation (Silurian) at surface, covers 1 % 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

Bloomsburg Formation (Silurian) at surface, covers < 0.1 % of this area

Bloomsburg Formation - Grayish-red siltstone, shale, and sandstone arranged in fining-upward cycles.

Lithology: siltstone; shale; sandstone

Quartz fanglomerate (Triassic) at surface, covers < 0.1 % of this area

Quartz fanglomerate - Well-rounded quartzite pebbles, cobbles, and rare boulders set in a reddish-brown, sandy matrix.

Lithology: conglomerate; quartzite; sand

Limestone fanglomerate (Triassic) at surface, covers < 0.1 % of this area

Limestone fanglomerate - Yellowish-gray to medium-gray, angular limestone and dolomite pebbles, cobbles, and fragments set in a red, very fine grained quartz matrix; a few shale-clast interbeds.

Lithology: conglomerate; dolostone (dolomite); limestone; shale