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.
Includes albite-chlorite schist, phyllite, some hornblende gneiss, and granitized members.
Chlorite-sericite schist containing interbedded quartzite.
Light-gray, locally mottled, massive, pure, coarsely crystalline dolomite; siliceous in middle part.
Gray and pale red, fine- to coarse-grained quartzose sandstone, siltstone, and mudstone.
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.
Very finely crystalline, light-gray limestone interbedded with gray dolomite; coarsely crystalline limestone lenses present.
Light-gray to buff, commonly arkosic sandstone interbedded with red shale, mudstone, and fine-grained sandstone
Medium-gray, finely crystalline dolomite; silty to sandy, containing numerous siliceous to argillaceous laminae.
Dark-gray, knotty, argillaceous dolomite; impure light-gray marble at base locally.
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
Gray, finely crystalline limestone containing dark-gray silty laminations; numerous edgewise conglomerate beds.
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.
Light, medium grained; predominantly quartz and feldspar of igneous origin.
Cobble and pebble quartz conglomerate interbedded with red sandstone.
Light-gray, hard, massive, Scolithus-bearing quartzite and quartz schist; thin, interbedded dark slate at top; conglomerate (Hellam Member) at base.
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.
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.
Pink to white and gray, finely laminated limestone and interbedded finely crystalline dolomite; numerous stromatolitic limestone beds.
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.
Gray, buff-weathering quartzite and quartz schist.
Reddish-brown to maroon, silty mudstone and shale containing thin red sandstone interbeds; several thin beds of impure limestone.
Light- to dark-gray, very finely to medium-crystalline dolomite containing interbeds of light-gray limestone; interbedded nodular, dark-gray chert at base.
Quartz or quartzite pebbles, cobbles, and rare boulders set in a red, sandy, ferruginous matrix; some silica cement; some feldspar clasts.
Thick-bedded, medium- to coarsely crystalline dolomite, in part oolitic, containing laminated limestone and sandstone interbeds.
Dark, fine to medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh."
Medium grained, light pink to greenish gray; largely quartz, feldspar, and mica; commonly gneissic, containing alteration minerals; interfingers with gabbroic gneiss.
Dark-greenish-gray phyllite and schist containing thin quartzite layers.
Includes serpentine, steatite, and other products of alteration of peridotites and pyroxenites.
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.
Bluish-black slate (Peach Bottom); quartz conglomerate having a matrix of sericite and chlorite (Cardiff).
Gray dolomite, in part oolitic, interbedded with medium-gray limestone and dark-gray oolitic chert.
Includes, in descending order, the Hershey and Myerstown Formations, undivided (Ohm) and Annville Formation (Oan).
Dark, medium grained; includes some rocks of probable sedimentary origin.
In descending order: Hershey--dark-gray to black, thin-bedded, argillaceous limestone; Myerstown--medium- to dark-gray, platy, medium-crystalline limestone; carbonaceous at base.
Light-gray to buff, coarse-grained, arkosic sandstone; includes reddish-brown to grayish-purple sandstone, siltstone, and mudstone.
Gray-green phyllite, mica-chlorite schist, and conglomerate.
Medium grained, medium to dark gray; locally gneissic, predominantly feldspar and quartz, plus dark accessories and various alteration minerals.
Light-gray, massive, high-calcium limestone; mottled at base.
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.
Ranges from fine- to medium-grained, altered gabbro to hornblende gneiss.
Altered basaltic flows, some amygdaloidal; green, schistose, containing hornblende, epidote, chlorite, and quartz.
Dark-gray, slaty to phyllitic shale, calcareous at base. Probably only lower part of Martinsburg Formation is present; overlain by Hamburg sequence rocks.
Dark-gray, fine-grained intrusives; locally, mineralogy is altered and unit has greenish color.
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.