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

Geologic units in Lehigh county, Pennsylvania

Martinsburg Formation (Ordovician) at surface, covers 30 % of this area

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

Lithology: shale

Diabase (Jurassic) at surface, covers 0.4 % 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

Beekmantown Group (Ordovician) at surface, covers 5 % 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

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

Felsic to mafic gneiss (Precambrian) at surface, covers 7 % of this area

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

Lithology: felsic gneiss; mafic gneiss; orthogneiss

Allentown Formation (Cambrian) at surface, covers 14 % 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

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

Quartz fanglomerate (Triassic) at surface, covers 4 % of this area

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

Lithology: conglomerate; quartzite; sand

Leithsville Formation (Cambrian) at surface, covers 4 % 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

Graywacke and shale of Martinsburg Formation (Ordovician) at surface, covers 10 % of this area

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

Lithology: graywacke

Hardyston Formation (Cambrian) at surface, covers 2 % 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

Rickenbach Formation (Ordovician) at surface, covers 1 % 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

Jacksonburg Formation (Ordovician) at surface, covers 3 % 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

Ontelaunee Formation (Ordovician) at surface, covers 1 % 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

Brunswick Formation (Triassic) at surface, covers 2 % 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 0.8 % 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 < 0.1 % 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

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

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

Lithology: limestone; dolostone (dolomite)

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

Shale and graywacke of Hamburg sequence (Ordovician) at surface, covers 6 % of this area

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

Lithology: shale; graywacke