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

Geologic units in York county, Pennsylvania

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

Vintage Formation - Dark-gray, knotty, argillaceous dolomite; impure light-gray marble at base locally.

Lithology: dolostone (dolomite); marble

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

Peach Bottom Slate and Cardiff Conglomerate, undivided (Probably lower Paleozoic) at surface, covers 0.2 % of this area

Peach Bottom Slate and Cardiff Conglomerate, undivided - Bluish-black slate (Peach Bottom); quartz conglomerate having a matrix of sericite and chlorite (Cardiff).

Lithology: slate; conglomerate

St. Paul Group (Ordovician) at surface, covers < 0.1 % 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)

Cardiff Metaconglomerate (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Cardiff Metaconglomerate - Silvery-gray, well foliated, micaceous quartz-pebble metaconglomerate and quartzite; apparent maximum thickness 700 feet.

Lithology: meta-conglomerate; quartzite

Diabase (Jurassic) at surface, covers 5 % 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

Metabasalt (Precambrian) at surface, covers 0.2 % of this area

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

Lithology: meta-basalt

Ultramafic rocks (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Ultramafic rocks - Includes serpentine, steatite, and other products of alteration of peridotites and pyroxenites.

Lithology: serpentinite; pyroxenite; peridotite

Marburg Schist (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Marburg Schist - Bluish-gray to silvery-green, fine-grained, muscovite-chlorite-albite-quartz schist; intensely cleaved and closely folded; contains interbedded quartzites.

Lithology: mica schist; quartzite

Montalto Member of Harpers Formation (Cambrian) at surface, covers 0.2 % of this area

Montalto Member of Harpers Formation - Gray quartzite.

Lithology: quartzite

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

Tomstown Formation - Massive dolomite containing thin shaly interbeds.

Lithology: dolostone (dolomite); shale

Gettysburg conglomerate (Triassic) at surface, covers 3 % of this area

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

Lithology: conglomerate; sandstone; siltstone; mudstone

Marburg Schist (Probably lower Paleozoic) at surface, covers 12 % of this area

Marburg Schist - Gray-green phyllite, mica-chlorite schist, and conglomerate.

Lithology: phyllite; mica schist; conglomerate

Wakefield Marble (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Wakefield Marble - White, fine-grained marble; subordinate white, green, and pink variegated marble; and blue marble.

Lithology: marble

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

Peach Bottom Slate (Ordovician (?)) at surface, covers < 0.1 % of this area

Peach Bottom Slate - Hard, bluish-black graphitic slate; thin beds of fine-grained black quartzite near base; apparent maximum thickness 1,000 feet.

Lithology: slate; quartzite

Conestoga Formation (Ordovician and Cambrian) at surface, covers 3 % of this area

Conestoga Formation - Light-gray, thin-bedded, impure, contorted limestone having shale partings; conglomeratic at base; in Chester Valley, includes micaceous limestone in upper part, phyllite in middle, and alternating dolomite and limestone in lower part.

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

Sams Creek Metabasalt (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Sams Creek Metabasalt - Grayish-green, massive to schistose, amygdaloidal metabasalt.

Lithology: meta-basalt

Gettysburg Formation (Triassic) at surface, covers 12 % 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

Antietam Formation (Cambrian) at surface, covers 0.4 % of this area

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

Lithology: quartzite; schist

Antietam and Harpers Formations, undivided (Cambrian) at surface, covers 10 % of this area

Antietam and Harpers Formations, undivided - Includes, in descending order, the Antietam (CAa) and Harpers (CAh) Formations. Antietam Formation - gray, buff-weathering quartzite. Harpers Formation - Dark-greenish-gray phyllite and schist containing thin quartzite layers; includes Montalto Member (CAhm) - gray quartztite

Lithology: quartzite; schist; phyllite

Octoraro Formation (Probably lower Paleozoic) at surface, covers 28 % of this area

Octoraro Formation - Includes albite-chlorite schist, phyllite, some hornblende gneiss, and granitized members.

Lithology: schist; phyllite; gneiss; granitoid

Buffalo Springs Formation (Cambrian) at surface, covers < 0.1 % of this area

Buffalo Springs Formation - Light-gray to pinkish-gray, finely to coarsely crystalline limestone and interbedded dolomite; numerous siliceous and clayey laminae; stromatolitic limestone beds near top; some thin sandy beds.

Lithology: limestone; dolostone (dolomite); sandstone

Limestone fanglomerate (Triassic) at surface, covers 0.3 % 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

Quartz fanglomerate (Triassic) at surface, covers 0.2 % of this area

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

Lithology: conglomerate; quartzite; sand

Peters Creek Schist (Probably lower Paleozoic) at surface, covers 2 % of this area

Peters Creek Schist - Chlorite-sericite schist containing interbedded quartzite.

Lithology: schist; quartzite

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

New Oxford conglomerate (Triassic) at surface, covers 0.2 % of this area

New Oxford conglomerate - Quartz or quartzite pebbles, cobbles, and rare boulders set in a red, sandy, ferruginous matrix; some silica cement; some feldspar clasts.

Lithology: conglomerate; quartzite; sand

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

Chickies Formation - Light-gray, hard, massive, Scolithus-bearing quartzite and quartz schist; thin, interbedded dark slate at top; conglomerate (Hellam Member) at base.

Lithology: quartzite; schist; slate; conglomerate

Metarhyolite (Precambrian) at surface, covers 0.3 % 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 < 0.1 % 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

Wissahickon Formation; Metagraywacke (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Wissahickon Formation; Metagraywacke - (Formerly mapped as Peters Creek Formation.) Rhythmically interbedded chlorite-muscovite meta-graywacke and fine-grained chlorite-muscovite schist; graded bedding locally preserved; thickness probably 2,000 to 3,000 feet.

Lithology: metasedimentary rock; schist

Heidlersburg Member of Gettysburg Formation (Triassic) at surface, covers 0.5 % of this area

Heidlersburg Member of Gettysburg Formation - Red, green, and gray shale and argillite, and minor thin beds of gray arkosic sandstone; some quartz conglomerate and limestone conglomerate.

Lithology: shale; argillite; arkose; conglomerate; limestone

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

Hamburg sequence rocks (Ordovician) at surface, covers 0.1 % 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

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

Ledger Formation - Light-gray, locally mottled, massive, pure, coarsely crystalline dolomite; siliceous in middle part.

Lithology: dolostone (dolomite)

Ultramafic Rocks (Early Paleozoic - Late Precambrian (?)) at surface, covers < 0.1 % of this area

Ultramafic Rocks - Chiefly serpentinite with partly to completely altered dunite, peridotite, pyroxenite, and massive to schistose soapstone; talc-carbonate rock and altered gabbro are common in some bodies.

Lithology: serpentinite; dunite; peridotite; pyroxenite; gabbro

Wissahickon Formation (Undivided) (Late Precambrian (?)) at surface, covers < 0.1 % of this area

Wissahickon Formation (Undivided) - Muscovite-chlorite-albite schist, muscovite-chlorite schist, chloritoid schist, and quartzite; intensely folded and cleaved.

Lithology: schist; quartzite

Wakefield Marble (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Wakefield Marble - Light gray, coarsely crystalline; contains graphite flakes in places.

Lithology: marble

Snitz Creek and Buffalo Springs Formations, undivided (Cambrian) at surface, covers < 0.1 % of this area

Snitz Creek and Buffalo Springs Formations, undivided - Includes, in descending order, the Snitz Creek (CAsc) and Buffalo Springs (CAbs) Formations. Snitz Creek Formation - thick-bedded. medium- to coarsely crystalline dolomite; in part oolitic, containing laminated limestone and sandstone interbeds. Buffalo Springs Formation - light-gray to pinkish-gray, finely to coarsely crystalline limestone and interbedded dolomite; numerous siliceous and clayey laminae; stromatolitic limestone beds near top; some thin sandy beds.

Lithology: limestone; dolostone (dolomite); sandstone

Sams Creek Metabasalt (Probably lower Paleozoic) at surface, covers 0.8 % of this area

Sams Creek Metabasalt - Altered basaltic flows, some amygdaloidal; green, schistose, containing hornblende, epidote, chlorite, and quartz.

Lithology: meta-basalt

New Oxford Formation (Triassic) at surface, covers 10 % of this area

New Oxford Formation - Light-gray to buff, commonly arkosic sandstone interbedded with red shale, mudstone, and fine-grained sandstone

Lithology: arkose; shale; mudstone; sandstone

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)

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

Kinzers Formation - Base--dark-brown shale; middle--gray and white spotted limestone and, locally, marble having irregular partings; top--sandy limestone which weathers to a fine-grained, friable, porous, sandy mass.

Lithology: limestone; marble; shale; sand