Geologic units in Lebanon county, Pennsylvania

Hamburg sequence rocks (Ordovician) at surface, covers 30 % of this area

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

Hammer Creek Formation (Triassic) at surface, covers 7 % of this area

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

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

Gray dolomite, in part oolitic, interbedded with medium-gray limestone and dark-gray oolitic chert.

Graywacke of Hamburg sequence (Ordovician) at surface, covers 4 % of this area

Predominantly graywacke.

Epler Formation (Ordovician) at surface, covers 4 % of this area

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

Stonehenge Formation (Ordovician) at surface, covers 4 % of this area

Gray, finely crystalline limestone containing dark-gray silty laminations; numerous edgewise conglomerate beds.

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

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.

Millbach and Schaefferstown Formations, undivided (Cambrian) at surface, covers 3 % of this area

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

Diabase (Jurassic) at surface, covers 3 % 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.

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

Thick-bedded, medium- to coarsely crystalline dolomite, in part oolitic, containing laminated limestone and sandstone interbeds.

Hammer Creek conglomerate (Triassic) at surface, covers 3 % of this area

Cobble and pebble quartz conglomerate interbedded with red sandstone.

Mauch Chunk Formation (Mississippian) at surface, covers 2 % of this area

Grayish-red shale, siltstone, sandstone, and some conglomerate; some local nonred zones. Includes Loyalhanna Member (crossbedded, sandy limestone) at base in south-central and southwestern Pennsylvania; also includes Greenbrier Limestone Member, and Wymps Gap and Deer Valley Limestones, which are tongues of the Greenbrier. Along Allegheny Front from Blair County to Sullivan County, Loyalhanna Member is greenish-gray, calcareous, crossbedded sandstone.

Hershey and Myerstown Formations, undivided (Ordovician) at surface, covers 2 % of this area

In descending order: Hershey--dark-gray to black, thin-bedded, argillaceous limestone; Myerstown--medium- to dark-gray, platy, medium-crystalline limestone; carbonaceous at base.

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

Light- to dark-gray, very finely to medium-crystalline dolomite containing interbeds of light-gray limestone; interbedded nodular, dark-gray chert at base.

Sherman Creek Member of Catskill Formation (Devonian) at surface, covers 2 % of this area

Alternating grayish-red mudstone and siltstone in poorly defined fining-upward cycles, and minor intervals of gray sandstone; laterally equivalent to Berry Run, Sawmill Run, Packerton, and Long Run Members of eastern Pennsylvania.

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

Gray to dark-gray, buff-weathering shale.

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

Conspicuous limestone.

Pottsville Formation (Pennsylvanian) at surface, covers 1 % of this area

Gray conglomerate, fine- to coarse-grained sandstone, and siltstone and shale containing minable anthracite coals. Includes three members, in descending order: Sharp Mountain--conglomerate and conglomeratic sandstone; Schuylkill--sandstone and conglomeratic sandstone; Tumbling Run--conglomeratic sandstone and sandstone.

Llewellyn Formation (Pennsylvanian) at surface, covers 1 % of this area

Gray, fine- to coarse-grained sandstone, siltstone, shale, conglomerate, and numerous anthracite coals in repetitive sequences.

Gettysburg Formation (Triassic) at surface, covers 1 % of this area

Reddish-brown to maroon, silty mudstone and shale containing thin red sandstone interbeds; several thin beds of impure limestone.

Hamilton Group (Devonian) at surface, covers 1 % of this area

Includes, in descending order, the Mahantango (Dmh) and Marcellus (Dmr) Formations.

Trimmers Rock Formation (Devonian) at surface, covers 1 % of this area

Olive-gray siltstone and shale, characterized by graded bedding; marine fossils; some very fine grained sandstone in northeast; black shale of Harrell Formation at base in Susquehanna Valley.

Bloomsburg Formation (Silurian) at surface, covers 1 % of this area

Grayish-red and greenish-gray shale, siltstone, and very fine to coarse-grained sandstone; some calcareous mudstone in central Pennsylvania; thins to west and is replaced by Mifflintown beds; thickens eastward, replacing overlying Wills Creek and Tonoloway Formations and underlying Mifflintown Formation.

Shale and graywacke of Hamburg sequence (Ordovician) at surface, covers 1 % of this area

Shale containing zones of conspicuous graywacke.

Rickenbach Formation (Ordovician) at surface, covers 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.

Jonestown Volcanic Suite (Ordovician) at surface, covers 1.0 % of this area

Andesite extrusives and dark-greenish-gray metadiabase. Metadiabase weathers medium gray to brown, forming rounded cobbles and boulders.

Irish Valley Member of Catskill Formation (Devonian) at surface, covers 0.8 % of this area

Nonmarine, grayish-red siltstone and mudstone, and gray and grayish-red sandstone interbedded with minor, thin, light-olive-gray marine siltstone; arranged in fining-upward cycles. Lower part of member has conglomeratic sandstones.

Martinsburg Formation (Ordovician) at surface, covers 0.8 % 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.

Felsic to mafic gneiss (Precambrian) at surface, covers 0.7 % of this area

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

Annville Formation (Ordovician) at surface, covers 0.7 % of this area

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

Pocono Formation (Mississippian) at surface, covers 0.6 % of this area

Light-gray to buff or light-olive-gray, medium-grained, crossbedded sandstone and minor siltstone; commonly conglomeratic at base and in middle; medial conglomerate, where present, is used to divide into Mount Carbon and Beckville Members; equivalent to Burgoon Sandstone of Allegheny Plateau.

Hornblende gneiss (Precambrian) at surface, covers 0.6 % of this area

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

Clinton Group (Silurian) at surface, covers 0.5 % of this area

Predominantly Rose Hill Formation--light-olive-gray to brownish-gray, fossiliferous shale; locally, limestone occurs near top; includes dark-reddish-gray, very fine to coarse-grained, ferruginous sandstone; east of Harrisburg, equivalent to Lizard Creek Member of Shawangunk Formation. Above Rose Hill is Keefer Formation--light- to dark-gray, fossiliferous sandstone, hematitic, oolitic sandstone, and shale; not recognized east of Harrisburg.

Shawangunk Formation (Silurian) at surface, covers 0.5 % 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.

Hardyston Formation (Cambrian) at surface, covers 0.4 % 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.

Leithsville Formation (Cambrian) at surface, covers 0.4 % 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.

Duncannon Member of Catskill Formation (Devonian) at surface, covers 0.4 % of this area

Grayish-red sandstone, siltstone, and mudstone in fining-upward cycles; conglomerate occurs at base of some cycles.

Spechty Kopf Formation (Mississippian and Devonian) at surface, covers 0.4 % of this area

Light- to olive-gray, fine- to medium- grained, crossbedded sandstone, siltstone, and local polymictic diamictite, pebbly mudstone, and laminite; arranged in crude fining-upward cycles in some places; locally has grayish-red shale near top and conglomerate at base and in middle.

Tuscarora Formation (Silurian) at surface, covers 0.4 % of this area

Light- to medium-gray quartzite and quartzitic sandstone and minor interbedded shale and siltstone, locally conglomeratic in lower part; includes (to the northwest) interbedded red and non-red sandstone (Castanea Member) at top; east of Harrisburg, equivalent to Minsi and Weiders Members of Shawangunk Formation.

Clarks Ferry Member of Catskill Formation (Devonian) at surface, covers 0.4 % of this area

Gray to yellowish-gray sandstone, siltstone, and conglomerate.

Limestone fanglomerate (Triassic) at surface, covers 0.3 % 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.

Onondaga Formation through Poxono Island Formation, undivided (Devonian and Silurian) at surface, covers 0.2 % of this area

In descending order: Onondaga Formation--gray calcareous, sandy shale; Ridgeley Formation--brown sandstone; Rondout Formation--gray interbedded limestone, dolomite, and shale; Decker Formation--gray calcareous sandstone, and Andreas Red Beds at top; Bossardville Limestone--gray, mud-cracked shaly limestone; Poxono Island Formation--olive-gray, calcareous and dolomitic shale, siltstone, and sandstone.

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

Light-gray to buff, commonly arkosic sandstone interbedded with red shale, mudstone, and fine-grained sandstone

Graphitic felsic gneiss (Precambrian) at surface, covers < 0.1 % of this area

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.