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

Geologic units in Bucks county, Pennsylvania

Hardyston Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area

Hardyston Quartzite (Lower Cambrian) (Wolff and Brooks, 1898) - Light- to medium-gray and bluish-gray conglomeratic sandstone. Varies from pebble conglomerate, to fine-grained, well-cemented quartzite, to arkosic or dolomitic sandstone. Conglomerate contains subangular to subrounded white quartz pebbles up to 2.5 cm (1 in.). Lower contact unconformable. About 0 to 9 m (1-30 ft) thick.

Lithology: quartzite; conglomerate; sandstone

Granitic gneiss and granite (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Granitic gneiss and granite - Includes Springfield Granodiorite (granitized Wissahickon) in Philadelphia area.

Lithology: granitic gneiss; granite; granodiorite

Passaic Formation Limestone-clast Conglomerate facies (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

Passaic Formation Limestone-clast Conglomerate facies - Limestone conglomerate unit (JTrpcl) is medium-bedded to massive, pebble to boulder conglomerate. Clasts are subangular dolomitic limestone in matrix of brownish- to purplish-red sandstone to mudstone; matrix weathers light-gray to white near faults. Maximum thickness unknown.

Lithology: conglomerate; limestone; sandstone; mudstone

Quartz-Oligoclase Gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Quartz-Oligoclase Gneiss - White-weathering, light-greenish-gray, medium- to coarse-grained, moderately layered to indistinctly foliated gneiss and lesser amounts of granofels composed of quartz, oligoclase or andesine, and, locally, biotite, hornblende and (or) clinopyroxene. Contains thin amphibolite layers.

Lithology: gneiss; granofels; amphibolite

Mafic gneiss (Precambrian) at surface, covers 0.5 % of this area

Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to "PZmgh" in places.

Lithology: mafic gneiss; paragneiss

Lockatong Formation (Triassic) at surface, covers 17 % of this area

Lockatong Formation - 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.

Lithology: argillite; shale; limestone; black shale

Brunswick Formation (Triassic) at surface, covers 30 % 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

Microperthite Alaskite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Microperthite Alaskite - Pink- to buff-weathering, light-pinkish-gray or pinkish-white, medium- to coarse-grained, gneissoid to indistinctly foliated granite composed principally of microcline microperthite, quartz and oligoclase. Includes small bodies of amphibolite not shown on map.

Lithology: granite; amphibolite

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

Wissahickon Formation (Probably lower Paleozoic) at surface, covers 2 % of this area

Wissahickon Formation - Includes oligoclase-mica schist, some hornblende gneiss, some augen gneiss, and some quartz-rich and feldspar-rich members due to various degrees of granitization.

Lithology: mica schist; mafic gneiss; augen gneiss; granitoid

Hornblende Granite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Hornblende Granite - Pinkish-gray- to medium-buff-weathering, pinkish-white or light-pinkish-gray, medium- to coarse-grained, gneissoid to indistinctly foliated granite and sparse granite gneiss composed principally of microcline microperthite, quartz, oligoclase, and hornblende. Some phases are quartz syenite or quartz monzonite. Includes small bodies of pegmatite and amphibolite not shown on map. U-Pb age approximately 1,090 Ma (Drake and others, 1991b).

Lithology: granite; paragneiss; quartz syenite; quartz monzonite; pegmatite; amphibolite

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

Franklin Marble - White, coarsely crystalline; disseminated graphite flakes.

Lithology: marble

Stockton Formation (Upper Triassic) at surface, covers 0.1 % of this area

Stockton Formation - Predominantly medium- to coarse-grained, light-gray, light-grayish-brown, or yellowish- to pinkish-gray arkosic sandstone and medium- to fine-grained, violet-gray to reddish-brown arkosic sandstone; with lesser, reddish to purplish-brown, silty mudstone, argillaceous siltstone, and shale. Some coarse-grained sandstone in lower part contains thick beds of conglomerate (Trsc) which have been mapped in the vicinity of Stockton. Sandstone, deposited in high-gradient stream channels, is mostly planar bedded with scoured bases containing pebble lags and mudstone rip-up clasts. Upper part of channel beds are burrowed. Large-scale trough crossbeds occur in some very coarse grained sandstone beds; smaller scale trough and climbing-ripple cross lamination occur in the upper part of channel sequences and in finer grained sandstone beds. Typical floodplain mudstones are irregularly thin bedded and extensively burrowed. Floodplain beds are thicker and more numerous in the central Newark basin, near the Delaware River. Thickness of the unit (including Trsc) near Stockton is about 1,240 m (4,068 ft).

Lithology: arkose; fine-grained mixed clastic; siltstone; shale

Potomac Formation (Upper Cretaceous, lower Cenomanian) at surface, covers < 0.1 % of this area

Potomac Formation - Predominantly clay to clay-silt, thinly laminated to thick-bedded, mottled red, white, and orange-brown, less commonly dark-gray and woody; interbedded with thin beds and lenses of very fine to medium-grained, massive, white to orange-brown, micaceous sand. Lithologies are typical of the shallow subsurface. Down dip, these lithologies interfinger with thin to thick beds of marine clay-silt, commonly glauconitic and locally shelly. Marine beds are most prevalent in the southernmost part of the southern sheet. Unit 3 was cored in its entirety at Freehold where it is approximately 75 m (246 ft) thick. In the core, the basal 6 m (20 ft) consists of red or mottled red and white clay interbedded with gravel and fine- to coarse-grained sand. The clay is pervaded by reddish-brown siderite. Most of the overlying beds consist of interbedded dark-colored clay, locally weathered to pale yellow or white, and fine- to medium-grained, light-colored sand. Layers that contain fine black carbonaceous material to large lignitized wood pieces are common in unit 3 in this core. At Toms River, the unit is about 60 m (197 ft) thick and consists of dark- to pale-gray clay, locally weathering to white or yellowish gray, and light-colored, micaceous sand. In general, the darker colored clay is more common in the upper part of the section. Locally, the sand has very small amounts of glauconite which may indicate some local marine influence during sedimentation. The age of unit 3 was determined from pollen in the nonmarine deposits and foraminifera in the marine sections. Typical forms found in Zone III in New Jersey are Ajatipollis sp. A, Tricolpites nemejci, T. vulgaris, Tricolporoidites bohemicus, Tricolporoidites sp. A, T. sp. B, and Tricolporopollenites sp. B (Doyle and Robbins, 1977). In the marine facies, Petters (1976) reports a planktic foraminiferal suite containing Praeglobotruncana delrioensis and Rotalipora greenhornensis. Both the pollen and foraminiferal assemblages suggest an early Cenomanian age.

Lithology: clay or mud; silt; sand

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 1 % 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 1 % 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

Hypersthene-Quartz-Oligoclase Gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Hypersthene-Quartz-Oligoclase Gneiss - Gray- to tan-weathering, greenish-gray to greenish-brown, medium-grained, moderately well layered and foliated, greasy-lustered gneiss of charnockitic affinity composed of andesine or oligoclase, quartz, clinopyroxene, hornblende, hypersthene, and sparse amounts of biotite. Commonly interlayered with amphibolite and mafic-rich quartz-plagioclase gneiss.

Lithology: gneiss; amphibolite

Allentown Formation (Cambrian) at surface, covers 1.0 % 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

Stockton Formation Cobble Conglomerate and Sandstone facies (Upper Triassic) at surface, covers < 0.1 % of this area

Stockton Formation Cobble Conglomerate and Sandstone facies - Predominantly medium- to coarse-grained, light-gray, light-grayish-brown, or yellowish- to pinkish-gray arkosic sandstone and medium- to fine-grained, violet-gray to reddish-brown arkosic sandstone; with lesser, reddish to purplish-brown, silty mudstone, argillaceous siltstone, and shale. Some coarse-grained sandstone in lower part contains thick beds of conglomerate (Trsc) which have been mapped in the vicinity of Stockton. Sandstone, deposited in high-gradient stream channels, is mostly planar bedded with scoured bases containing pebble lags and mudstone rip-up clasts. Upper part of channel beds are burrowed. Large-scale trough crossbeds occur in some very coarse grained sandstone beds; smaller scale trough and climbing-ripple cross lamination occur in the upper part of channel sequences and in finer grained sandstone beds. Typical floodplain mudstones are irregularly thin bedded and extensively burrowed. Floodplain beds are thicker and more numerous in the central Newark basin, near the Delaware River. Thickness of the unit (including Trsc) near Stockton is about 1,240 m (4,068 ft).

Lithology: conglomerate

Gneiss granofels and Migmatite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Gneiss granofels and Migmatite - Gneiss and granofels range in composition from felsic to intermediate to mafic; intermediate compositions predominate. Contains a wide variety of rock types including graphitic schist and marble. Many rocks were injected by a granitoid that has blue quartz and augen of potassic feldspar and are arteritic migmatites. One body of gneiss contains a 1 m by 0.5 m (3 by 2 ft) phacoid of gabbro that is interpreted to be an olistolith. Unit probably represents a sequence of meta-sedimentary and metavolcanic rocks that have been heavily injected and migmatized by felsic magma.

Lithology: gneiss; granofels; schist; marble; migmatite

Hardyston Formation (Cambrian) at surface, covers 0.6 % 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

Diabase (Jurassic) at surface, covers < 0.1 % of this area

Diabase - Concordant to discordant, predominantly sheet-like intrusions of medium- to fine-grained diabase and dikes of fine-grained diabase; dark-greenish-gray to black; subophitic texture. Dense, hard, sparsely fractured rock composed mostly of plagioclase (An50-70), clinopyroxene (mostly augite), and magnetite-ilmenite. Orthopyroxene (En75-80) is locally abundant in the lower part of the sheets. Accessory minerals include apatite, quartz, alkali feldspar, hornblende, sphene, zircon, and rare olivine. Diabase in the map area was derived primarily from high-titanium, quartz-tholeiite magma. Sedimentary rocks within about 300 m (984 ft) above and 200 m (656 ft) below major diabase sheets are thermally metamorphosed. Red mudstone is typically altered to indurated, bluish-gray hornfels with clots or crystals of tourmaline or cordierite. Gray argillitic siltstone is typically altered to brittle, black, very fine grained hornfels. Sills are 365 to 400 m (1,197-1,312 ft) thick. Dikes range in thickness from 3 to 10 m (10-33 ft) and are many kilometers long.

Lithology: diabase

Chickies Formation (Cambrian) at surface, covers 0.5 % of this area

Chickies Formation - Light-gray, hard, massive, Scolithus-bearing quartzite and quartz schist; thin, interbedded dark slate at top; conglomerate (Hellam Member) at base.

Lithology: quartzite; schist; slate; conglomerate

Passaic Formation (Lower Jurassic and Upper Triassic) at surface, covers 0.1 % of this area

Passaic Formation - Predominantly red beds consisting of argillaceous siltstone; silty mudstone; argillaceous, very fine grained sandstone; and shale; mostly reddish-brown to brownish-purple, and grayish-red. Red beds occur typically in 3- to 7-m (10- to 23-ft-)-thick, cyclic playa-lake-mudflat sequences and fining-upward fluvial sequences. Lamination is commonly indistinct due to burrowing, desiccation, and paleosol formation. Where layering is preserved, most bedforms are wavy parallel lamination and trough and climbing-ripple cross lamination. Calcite- or dolomite-filled vugs and flattened cavities, mostly 0.5 to 0.2 mm (0.02-0.08 in) across, occur mostly in the lower half. Sand-filled burrows, 2 to 5 mm (0.08-0.2 in) in diameter, are prevalent in the upper two-thirds of the unit. Desiccation cracks, intraformational breccias, and curled silt laminae are abundant in the lower half. Lake cycles, mostly 2 to 5 m (7-16 ft) thick, have a basal, greenish-gray, argillaceous siltstone; a medial, dark-gray to black, pyritic, carbonaceous, fossiliferous, and, in places, calcareous lake-bottom fissile mudstone or siltstone; and an upper thick-bedded, gray to reddish and purplish-gray argillaceous siltstone with desiccation cracks, intraformational breccias, burrows, and mineralized vugs. Thickness of the formation between Sourland Mountain and Sand Brook syncline is about 3,500 m (11,483 ft).

Lithology: siltstone; sandstone; shale

Lockatong Formation (Upper Triassic) at surface, covers < 0.1 % of this area

Lockatong Formation - Predominantly cyclic lacustrine sequences of silty, dolomitic or analcime-bearing argillite; laminated mudstone; silty to calcareous, argillaceous very fine grained sandstone and pyritic siltstone; and minor silty limestone, mostly light- to dark-gray, greenishgray, and black. Grayish-red, grayish-purple, and dark-brownish-red sequences (Trlr) occur in some places, especially in upper half. Two types of cycles are recognized: freshwater-lake (detrital) and alkaline-lake (chemical) cycles. Freshwater-lake cycles average 5.2 m (17 ft) thick. They consist of basal, transgressive, fluvial to lake-margin deposits that are argillaceous, very fine grained sandstone to coarse siltstone with indistinct lamination, planar or cross lamination, or are disrupted by convolute bedding, desiccation cracks, root casts, soil-ped casts, and tubes. Medial lake-bottom deposits are laminated siltstones, silty mudstones, or silty limestones that are dark gray to black with calcite laminae and grains and lenses, or streaks of pyrite; fossils are common, including fish scales and articulated fish, conchostracans, plants, spores, and pollen. Upper regressive lake margin, playa lake, and mudflat deposits are light- to dark-gray silty mudstone to argillitic siltstone or very fine grained sandstone, mostly thick bedded to massive, with desiccation cracks, intraformational breccias, faint wavy laminations, burrows, euhedral pyrite grains, and dolomite or calcite specks. Alkaline-lake cycles are similar to freshwater-lake cycles, but are thinner, averaging 3 m (10 ft), have fewer fossils (mainly conchostracans), and commonly have red beds, extensive desiccation features, and abundant analcime and dolomite specks in the upper parts of cycles. Thickness near Byram is about 1,070 m (3,510 ft). The formation thins to the southeast and northeast; thickness near Princeton is less than 700 m (2,297 ft).

Lithology: argillite; mudstone; sandstone; siltstone; limestone

Passaic Formation gray bed (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

Passaic Formation gray bed - Upper Triassic gray lake deposits (Trpg) consist of gray to black silty mudstone, gray and greenish- to purplish-gray argillaceous siltstone, black shale, and medium- to dark-gray, argillaceous, fine-grained sandstone and are abundant in the lower half of the Passaic Formation. Gray lakebeds occur in groups of two to five cycles although they also occur as single cycles in some parts of the formation. Several lakebed sequences consisting of one or two thick groups of drab-colored beds as much as 30 m (98 ft) thick or more can be traced over tens of kilometers. Many gray-bed sequences are locally correlated within fault blocks; some can be correlated across major faults or intrusive rock units. Thickness of the (entire Passaic) formation between Sourland Mountain and Sand Brook syncline is about 3,500 m (11,483 ft).

Lithology: fine-grained mixed clastic; siltstone; black shale; sandstone

Felsic to mafic gneiss (Precambrian) at surface, covers 0.5 % of this area

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

Lithology: felsic gneiss; mafic gneiss; orthogneiss

Amphibolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Amphibolite - Gray- to grayish-black, medium-grained amphibolite composed of hornblende and andesine. Some phases contain biotite and (or) clinopyroxene. Ubiquitous and associated with almost all other Middle Proterozoic units. Some amphibolite is clearly metavolcanic in origin, some is metasedimentary, and some appears to be metagabbro.

Lithology: amphibolite

Passaic Formation Quatzite-clast Conglomerate facies (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

Passaic Formation Quartzite-clast Conglomerate facies - Quartzite conglomerate unit (JTrpcq) is reddish-brown pebble conglomerate, pebbly sandstone, and sandstone, in upward-fining sequences 1 to 2 m (3-6 ft) thick. Clasts are subangular to subrounded, quartz and quartzite in sandstone matrix. Sandstone is medium to coarse grained, feldspathic (up to 20 percent feldspar), and locally contains pebble and cobble layers. Conglomerate thickness exceeds 850 m (2,790 ft).

Lithology: conglomerate; sandstone

Hornblende gneiss (Precambrian) at surface, covers 0.5 % of this area

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

Lithology: mafic gneiss; paragneiss

Trenton Gravel (Quaternary) at surface, covers 8 % of this area

Trenton Gravel - Gray or pale-reddish-brown, very gravelly sand interstratified with crossbedded sand and clay-silt beds; includes areas of Holocene alluvium and swamp deposits.

Lithology: sand; clay or mud; silt; gravel; alluvium

Felsic gneiss (Precambrian) at surface, covers 2 % of this area

Felsic gneiss - Light, medium grained; includes rocks of probable sedimentary origin.

Lithology: felsic gneiss; paragneiss

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

Cocalico Formation - 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.

Lithology: shale; siltstone; sandstone

Beekmantown Group (Ordovician) at surface, covers 0.2 % 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

Bryn Mawr Formation (Tertiary) at surface, covers 0.2 % of this area

Bryn Mawr Formation - High-level terrace deposits; reddish-brown gravelly sand and some silt. Age uncertain.

Lithology: gravel; sand; silt

Stockton Formation (Triassic) at surface, covers 19 % of this area

Stockton Formation - Light-gray to buff, coarse-grained, arkosic sandstone; includes reddish-brown to grayish-purple sandstone, siltstone, and mudstone.

Lithology: arkose; siltstone; sandstone; mudstone

Pensauken and Bridgeton Formations, undifferentiated (Tertiary) at surface, covers 4 % of this area

Pensauken and Bridgeton Formations, undifferentiated - Dark-reddish-brown, cross-stratified, feldspathic quartz sand and some thin beds of fine gravel and rare layers of clay or silt.

Lithology: sand; gravel; clay or mud; silt

Stockton conglomerate (Triassic) at surface, covers 0.7 % of this area

Stockton conglomerate - Quartz cobbles set in a poorly sorted, sandy matrix; includes conglomeratic sandstone.

Lithology: conglomerate; sand; sandstone

Passaic Formation Conglomerate and Sandstone facies (Lower Jurassic and Upper Triassic) at surface, covers < 0.1 % of this area

Passaic Formation Conglomerate and Sandstone facies - Conglomeratic sandstone (JTrpsc) is brownish-red pebble conglomerate, medium- to coarse-grained, feldspathic sandstone and micaceous siltstone; unit is planar to low-angle trough cross laminated, burrowed, and contains local pebble layers. Unit forms upward-fining sequences 0.5 to 2.5 m (1.6-8 ft) thick. Conglomeratic sandstone thickness exceeds 800 m (2,625 ft).

Lithology: conglomerate; sandstone; siltstone

Mafic gneiss (Probably lower Paleozoic) at surface, covers 0.2 % of this area

Mafic gneiss - Dark, medium grained; includes rocks of probable sedimentary origin; may be equivalent to pCAmgh in places.

Lithology: mafic gneiss; paragneiss

Leithsville Formation (Middle and Lower Cambrian) at surface, covers < 0.1 % of this area

Leithsville Formation (Middle and Lower Cambrian) (Wherry, 1909) - Light- to dark-gray and lightolive-gray, fine- to medium-grained, thin- to medium-bedded dolomite. Grades downward through medium-gray, grayish-yellow, or pinkish-gray dolomite and dolomitic sandstone, siltstone and shale to medium-gray, medium-grained, medium-bedded dolomite containing quartz sand grains as stringers and lenses near the base. Lower contact gradational. Thickness ranges from 0 to 56 m (0-185 ft) due to erosion.

Lithology: dolostone (dolomite); shale; siltstone; sandstone

Diabase (Jurassic) at surface, covers 11 % 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

Ultramafic rocks (Probably lower Paleozoic) at surface, covers < 0.1 % of this area

Ultramafic rocks - Includes serpentine, steatite, and other products of alteration of peridotites and pyroxenites.

Lithology: serpentinite; pyroxenite; peridotite

Manhattan Schist (Lower Cambrian and (or) Late Proterozoic) at surface, covers < 0.1 % of this area

Manhattan Schist (Hall, in press) - Medium-dark gray, medium- to coarse-grained schist and gneiss composed of biotite, muscovite, quartz, and plagioclase, and local accessory minerals sillimanite, kyanite, tourmaline, and garnet. Contains some interlayered amphibolite. Unit is not exposed in the map area, but is present in boring logs.

Lithology: schist; gneiss; amphibolite

Allentown Dolomite (Lower Ordovician and Upper Cambrian) (Wherry, 1909) (Lower Ordovician and Upper Cambrian) at surface, covers < 0.1 % of this area

Allentown Dolomite (Lowest Lower Ordovician and Upper Cambrian) (Wherry, 1909) - Medium- to very light gray, fine- to medium-grained, very thin to very thick bedded dolomite containing minor orthoquartzite and shale. Oolites and algal stromatolites occur throughout unit. Shaly dolomite increases downward towards lower conformable contact with the Leithsville Formation. Unit does not crop out but is known from subsurface borings near Flanders (Volkert and others, 1990). Thickness ranges from 0 to 73 m (0-240 ft) due to erosion.

Lithology: dolostone (dolomite); orthoquartzite; shale