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

Geologic units in Lancaster county, Pennsylvania

Ledger Formation (Cambrian) at surface, covers 7 % of this area

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

Lithology: dolostone (dolomite)

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

Millbach Formation - Pink to white and gray, finely laminated limestone and interbedded finely crystalline dolomite; numerous stromatolitic limestone beds.

Lithology: limestone; dolostone (dolomite)

Felsic and intermediate gneiss (Precambrian) at surface, covers 0.4 % of this area

Felsic and intermediate gneiss - Medium grained, light pink to greenish gray; largely quartz, feldspar, and mica; commonly gneissic, containing alteration minerals; interfingers with gabbroic gneiss.

Lithology: felsic gneiss; gneiss

Banded mafic gneiss (Precambrian) at surface, covers 0.5 % of this area

Banded mafic gneiss - Dark, fine to medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh."

Lithology: mafic gneiss; paragneiss

Stonehenge Formation (Ordovician) at surface, covers 3 % 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

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

Annville Formation - Light-gray, massive, high-calcium limestone; mottled at base.

Lithology: limestone

New Oxford Formation (Triassic) at surface, covers 5 % 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

Snitz Creek and Buffalo Springs Formations, undivided (Cambrian) at surface, covers 2 % 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 < 0.1 % of this area

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

Lithology: meta-basalt

Kinzers Formation (Cambrian) at surface, covers 1 % 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

Epler Formation (Ordovician) at surface, covers 6 % of this area

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

Lithology: limestone; dolostone (dolomite)

Gettysburg Formation (Triassic) at surface, covers 0.8 % 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

Ontelaunee Formation (Ordovician) at surface, covers 0.6 % of this area

Ontelaunee Formation - Light- to dark-gray, very finely to medium-crystalline dolomite containing interbeds of light-gray limestone; interbedded nodular, dark-gray chert at base.

Lithology: dolostone (dolomite); limestone; chert

Zooks Corner Formation (Cambrian) at surface, covers 4 % of this area

Zooks Corner Formation - Medium-gray, finely crystalline dolomite; silty to sandy, containing numerous siliceous to argillaceous laminae.

Lithology: dolostone (dolomite)

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

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

Lithology: quartzite; schist

Graphitic felsic gneiss (Precambrian) at surface, covers 0.3 % of this area

Graphitic felsic gneiss - Includes Pickering Gneiss and small areas of marble; dominantly quartz and feldspar with varying amounts of graphite and various metamorphic minerals; medium grained, light to dark gray and greenish gray; sedimentary origin.

Lithology: gneiss; marble; paragneiss

Antietam and Harpers Formations, undivided (Cambrian) at surface, covers 3 % 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

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

Peters Creek Schist (Probably lower Paleozoic) at surface, covers 9 % of this area

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

Lithology: schist; quartzite

Graphitic felsic gneiss (Precambrian) at surface, covers < 0.1 % of this area

Graphitic felsic gneiss - Medium grained, medium to dark gray; locally gneissic, predominantly feldspar and quartz, plus dark accessories and various alteration minerals.

Lithology: felsic gneiss; mafic gneiss

Octoraro Formation (Probably lower Paleozoic) at surface, covers 11 % 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 3 % 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

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

Hardyston Formation - Typically light-gray, fine- to medium-grained quartzite, and feldspathic sandstone; color ranges from nearly white to dark gray; massive bedded; Scolithus present in upper part; quartz-pebble conglomerate occurs at base.

Lithology: quartzite; sandstone; conglomerate

Harpers Formation (Cambrian) at surface, covers 0.4 % 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 0.6 % 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 2 % 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

Felsic to mafic gneiss (Precambrian) at surface, covers 2 % of this area

Felsic to mafic gneiss - Light, medium grained; predominantly quartz and feldspar of igneous origin.

Lithology: felsic gneiss; mafic gneiss; orthogneiss

Marburg Schist (Probably lower Paleozoic) at surface, covers 0.1 % of this area

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

Lithology: phyllite; mica schist; conglomerate

Hershey Formation through Annville Formation, undivided (Ordovician) at surface, covers 0.2 % of this area

Hershey Formation through Annville Formation, undivided - Includes, in descending order, the Hershey and Myerstown Formations, undivided (Ohm) and Annville Formation (Oan).

Lithology: limestone

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

Snitz Creek Formation - Thick-bedded, medium- to coarsely crystalline dolomite, in part oolitic, containing laminated limestone and sandstone interbeds.

Lithology: dolostone (dolomite); limestone; sandstone

Hornblende gneiss (Precambrian) at surface, covers 0.1 % of this area

Hornblende gneiss - Dark, medium grained; includes some rocks of probable sedimentary origin.

Lithology: mafic gneiss; paragneiss

Cocalico Formation (Ordovician) at surface, covers 6 % of this area

Cocalico Formation - Gray phyllitic shale, maroon shale, siltstone, and silty, siliceous shale; some interbedded argillaceous and quartzose sandstone; predominantly allochthonous, and probably closely related to Hamburg sequence, but includes some autochthonous elements.

Lithology: shale; siltstone; sandstone

Conestoga Formation (Ordovician and Cambrian) at surface, covers 13 % 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

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

Richland Formation - Gray dolomite, in part oolitic, interbedded with medium-gray limestone and dark-gray oolitic chert.

Lithology: dolostone (dolomite); limestone; chert

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

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

Lithology: dolostone (dolomite); marble

Stockton Formation (Triassic) at surface, covers 0.1 % of this area

Stockton Formation - Light-gray to buff, coarse-grained, arkosic sandstone; includes reddish-brown to grayish-purple sandstone, siltstone, and mudstone.

Lithology: arkose; siltstone; sandstone; mudstone

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

Hammer Creek Formation (Triassic) at surface, covers 7 % of this area

Hammer Creek Formation - Gray and pale red, fine- to coarse-grained quartzose sandstone, siltstone, and mudstone.

Lithology: sandstone; siltstone; mudstone

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

Metagabbro - Ranges from fine- to medium-grained, altered gabbro to hornblende gneiss.

Lithology: mafic gneiss; gabbro

Hammer Creek conglomerate (Triassic) at surface, covers 2 % of this area

Hammer Creek conglomerate - Cobble and pebble quartz conglomerate interbedded with red sandstone.

Lithology: conglomerate; sandstone

Peach Bottom Slate and Cardiff Conglomerate, undivided (Probably lower Paleozoic) at surface, covers 0.3 % 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

Diabase (Jurassic) at surface, covers 2 % 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

Ultramafic rocks (Probably lower Paleozoic) at surface, covers 0.4 % of this area

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

Lithology: serpentinite; pyroxenite; peridotite

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

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

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

Lithology: shale