Geologic units in Lehigh county, Pennsylvania

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

Gray to dark-gray shale and slate.

Allentown Formation (Cambrian) at surface, covers 14 % of this area

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.

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

Shale containing conspicuous graywacke; includes autochthonous sandstone and shale of Shochary Ridge.

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

Light, medium grained; predominantly quartz and feldspar of igneous origin.

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

Thick-bedded, medium- to medium-dark-gray, finely crystalline limestone, weathering light gray; yellow dolomitic laminae; interbedded medium-dark-gray, finely crystalline dolomite, weathering yellowish gray; edgewise conglomerate; fossil-fragment and oolitic lenses.

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

Shale containing zones of conspicuous graywacke.

Beekmantown Group (Ordovician) at surface, covers 5 % of this area

Includes, in descending order, the Ontelaunee (Oo), Epler (Oe), Rickenbach (Ori), and Stonehenge (Os) Formations.

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

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

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

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.

Jacksonburg Formation (Ordovician) at surface, covers 3 % of this area

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

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

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

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

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.

Brunswick Formation (Triassic) at surface, covers 2 % of this area

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.

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

Medium- to dark-gray, coarsely crystalline dolomite in lower part; medium- to medium-light-gray, finely crystalline dolomite in upper part; chert lenses, beds, and nodules.

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

Medium-dark-gray, finely crystalline dolomite, massive to finely laminated; weathers grayish yellow; thick-bedded, dark-gray chert at base.

Shawangunk Formation (Silurian) at surface, covers 0.8 % of this area

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.

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

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

Diabase (Jurassic) at surface, covers 0.4 % of this area

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.

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

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

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

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.

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

Medium-light-gray to medium-gray, finely crystalline, thick-bedded limestone, containing dark siliceous laminae, edgewise conglomerate beds, and fossil-fragment lenses; dolomite beds increase in number eastward.

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

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.

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

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

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

Dark-gray, slaty to phyllitic shale, calcareous at base. Probably only lower part of Martinsburg Formation is present; overlain by Hamburg sequence rocks.