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.
Light-gray to buff, coarse-grained, arkosic sandstone; includes reddish-brown to grayish-purple sandstone, siltstone, and mudstone.
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.
Includes oligoclase-mica schist, some hornblende gneiss, some augen gneiss, and some quartz-rich and feldspar-rich members due to various degrees of granitization.
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.
Light, medium grained; includes rocks of probable sedimentary origin.
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.
Light-gray, locally mottled, massive, pure, coarsely crystalline dolomite; siliceous in middle part.
Light-gray, hard, massive, Scolithus-bearing quartzite and quartz schist; thin, interbedded dark slate at top; conglomerate (Hellam Member) at base.
Microcrystalline limestone and, in places, marble; includes subordinate dolomite containing abundant phyllitic layers; occurs in Chester and Montgomery Counties; relation to Elbrook of Cumberland Valley sequence is uncertain.
Includes albite-chlorite schist, phyllite, some hornblende gneiss, and granitized members.
Includes Springfield Granodiorite (granitized Wissahickon) in Philadelphia area.
Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh" in places.
Intensely colored, variegated, ferruginous clay and, in places, beds of sand; occurs in isolated patches.
Dark-reddish-brown, cross-stratified, feldspathic quartz sand and some thin beds of fine gravel and rare layers of clay or silt.
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
High-level terrace deposits; reddish-brown gravelly sand and some silt. Age uncertain.
Includes serpentine, steatite, and other products of alteration of peridotites and pyroxenites.
Lithologically similar to oligoclase-mica schist of the Wissahickon Formation (PZw), but also includes lenticular amphibolite bodies having ocean-floor basalt chemistry.
Dark-gray, fine-grained intrusives; locally, mineralogy is altered and unit has greenish color.
Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgh in places.
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.
Well-rounded quartzite pebbles, cobbles, and rare boulders set in a reddish-brown, sandy matrix.
Quartz cobbles set in a poorly sorted, sandy matrix; includes conglomeratic sandstone.