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

Geologic units in Berks county, Pennsylvania

Lower (Middle?) Cambrian rocks, undivided (Cambrian) at surface, covers 0.5 % of this area

Lower (Middle?) Cambrian rocks, undivided - Lower Cambrian of Berks County includes tectonic slices of many of the following rock units: Zooks Corner (CAzc), Ledger (CAl), Kinzers (CAk), Vintage (CAv), Antietam (CAa, CAah), and Harpers (CAh, CAah) Formations.

Lithology: dolostone (dolomite); limestone; shale; quartzite; phyllite; schist; marble

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

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

Lithology: shale

Juniata and Bald Eagle Formations, undivided (Ordovician) at surface, covers < 0.1 % 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

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

Hammer Creek conglomerate (Triassic) at surface, covers 6 % of this area

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

Lithology: conglomerate; sandstone

Hammer Creek Formation (Triassic) at surface, covers 4 % of this area

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

Lithology: sandstone; siltstone; mudstone

Hershey and Myerstown Formations, undivided (Ordovician) at surface, covers 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

Beekmantown Group (Ordovician) at surface, covers 1 % of this area

Beekmantown Group - Includes, in descending order, the Pinesburg Station (Ops), Rockdale Run (Orr), and Stonehenge (Os) Formations.

Lithology: limestone; dolostone (dolomite); chert

Stockton Formation (Triassic) at surface, covers 0.8 % 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

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

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

Lithology: dolostone (dolomite); marble

Richland Formation (Cambrian) at surface, covers 1 % 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

Hornblende gneiss (Precambrian) at surface, covers 3 % of this area

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

Lithology: mafic gneiss; paragneiss

Snitz Creek Formation (Cambrian) at surface, covers < 0.1 % 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

Limestone of Hamburg sequence (Ordovician) at surface, covers 1 % of this area

Limestone of Hamburg sequence - Conspicuous limestone.

Lithology: limestone

Felsic to mafic gneiss (Precambrian) at surface, covers 10 % of this area

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

Lithology: felsic gneiss; mafic gneiss; orthogneiss

Graywacke and shale of Martinsburg Formation (Ordovician) at surface, covers 0.7 % of this area

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

Lithology: graywacke

Chickies Formation (Cambrian) at surface, covers < 0.1 % 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

Hardyston Formation (Cambrian) at surface, covers 3 % 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

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

Allentown Formation - Medium- to medium-dark-gray, thick-bedded dolomite and impure limestone; dark-gray chert stringers and nodules; laminated; oolitic and stromatolitic; some orange-brown-weathering calcareous siltstone at base.

Lithology: dolostone (dolomite); limestone; chert; siltstone

Buffalo Springs Formation (Cambrian) at surface, covers 0.4 % 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 0.9 % 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

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

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

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

Leithsville Formation - Medium- to dark-gray, crystalline dolomite, light-olive-gray in places, weathering to light gray and yellowish brown; massive bedded; oolitic; pink to gray, mottled chert and dark-gray chert; thin shale and dolomitic shale interbeds; scattered sand grains; upper part is very shaly.

Lithology: dolostone (dolomite); shale; chert; sand

Millbach and Schaefferstown Formations, undivided (Cambrian) at surface, covers < 0.1 % of this area

Millbach and Schaefferstown Formations, undivided - Includes, in descending order, the Millbach Formation (CAm), and the Schaefferstown Formation--gray limestone containing siliceous and argillaceous laminae; thin bedded.

Lithology: limestone; dolostone (dolomite); shale

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

Franklin Marble - White, coarsely crystalline; disseminated graphite flakes.

Lithology: marble

Antietam and Harpers Formations, undivided (Cambrian) at surface, covers < 0.1 % 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

Graphitic felsic gneiss (Precambrian) at surface, covers 0.5 % 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

Graywacke of Hamburg sequence (Ordovician) at surface, covers < 0.1 % of this area

Graywacke of Hamburg sequence - Predominantly graywacke.

Lithology: graywacke

Rickenbach Formation (Ordovician) at surface, covers 0.9 % of this area

Rickenbach Formation - Gray, very finely to coarsely crystalline, laminated dolomite; dark-gray chert in irregular beds, stringers, and nodules; bands of quartz sand grains in lower half.

Lithology: dolostone (dolomite); chert

Ontelaunee Formation (Ordovician) at surface, covers 2 % 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 0.2 % of this area

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

Lithology: dolostone (dolomite)

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

Jacksonburg Formation - Dark-gray shaly limestone (cement rock) having slaty cleavage; basal medium- to thick-bedded limestone (cement limestone) increases in thickness eastward.

Lithology: limestone; shale

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

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

Lithology: limestone; dolostone (dolomite)

Brunswick Formation (Triassic) at surface, covers 6 % of this area

Brunswick Formation - Reddish-brown mudstone, siltstone, and shale, containing a few green and brown shale interbeds; red and dark-gray, interbedded argillites near base. Youngest beds in Brunswick may be Jurassic in age.

Lithology: mudstone; siltstone; shale; argillite

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

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

Lithology: mafic metavolcanic rock

Shawangunk Formation (Silurian) at surface, covers 3 % of this area

Shawangunk Formation - Light- to dark-gray, fine- to very coarse grained sandstone and conglomerate containing thin shale interbeds. Includes four members, in descending order: Tammany--conglomerate and sandstone; Lizard Creek--sandstone and red or green shale; Minsi--sandstone and conglomerate; Weiders--conglomerate. Tammany and Lizard Creek Members together are approximately equivalent to Clinton Group to the west; Minsi and Weiders Members together are equivalent to Tuscarora Formation to the west.

Lithology: sandstone; conglomerate; shale

Stonehenge Formation (Ordovician) at surface, covers 0.4 % 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

Sedimentary strata at Jacksonwald and Aspers (Jurassic) at surface, covers < 0.1 % of this area

Sedimentary strata at Jacksonwald and Aspers - Arkosic sandstone; fossiliferous, gray to black shale and limestone; ripple-cross-laminated siltstone; and boulder conglomerate.

Lithology: arkose; shale; limestone; siltstone; conglomerate

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

Lockatong Formation - Dark-gray to black, thick-bedded argillite containing a few zones of thin-bedded black shale; locally has thin layers of impure limestone and calcareous shale.

Lithology: argillite; shale; limestone; black shale

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

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

Lithology: limestone

Shale and graywacke of Hamburg sequence (Ordovician) at surface, covers 20 % of this area

Shale and graywacke of Hamburg sequence - Shale containing zones of conspicuous graywacke.

Lithology: shale; graywacke

Felsic and intermediate gneiss (Precambrian) at surface, covers 0.1 % 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

Hamburg sequence rocks (Ordovician) at surface, covers 15 % 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 < 0.1 % 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 0.5 % 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)