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Geologic units containing slate

Earth material > Metamorphic rock > Metasedimentary rock

Slate

A compact, fine-grained metamorphic rock that possesses slaty cleavage and hence can be split into slabs and thin plates

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Alabama - Arizona - California - Colorado - Georgia - Iowa - Idaho - Massachusetts - Maryland - Maine - Michigan - Minnesota - North Carolina - New Hampshire - New Jersey - New York - Oregon - Pennsylvania - Rhode Island - South Dakota - Tennessee - Texas - Virginia - Vermont - Washington - Wisconsin

Alabama

Kahatchee Mountain Group; Brewer Phyllite (Precambrian?-Cambrian?): Brewer Phyllite - dusky-red micaceous slate and phyllite, locally containing interbedded micaceous arkosic quartzite and metasiltstone; locally at the base is interbedded calcite and dolomite marble.
Kahatchee Mountain Group; Wash Creek Slate (Precambrian?-Cambrian?): Wash Creek Slate - grayish-green to black micaceous, partly carbonaceous to graphitic slate and metasiltstone containing interbedded light-gray to light-brown fine to coarse-grained metasandstone.
Kahatchee Mountain Group; Waxahatchee Slate (Precambrian?-Cambrian?): Waxahatchee Slate - dark-gray to grayish-green thin-bedded, micaceous metasiltstone, slate, and fine-grained quartzite.
Metaclastic rocks of unknown affinity (Precambrian to Paleozoic): Metaclastic rocks of unknown affinity - in the area south of Talladega, Talladega County, the unit includes greenish-gray chlorite-sericite phyllite; in small area south of Childersburg the unit consists of greenish-gray chlorite-sericite phyllite and slate locally containing interbeds of metagraywacke; and in the area east of Columbiana, Shelby County, the unit includes dark-greenish-gray slate and metasiltstone containing interbedded coarse-grained to conglomerate quartzite.
Sylacauga Marble Group; Fayetteville Phyllite (Cambrian?-Ordovician?): Fayetteville Phyllite - dusky-red and medium-gray phyllite and slate interlayered with light-brown to light-gray feldspathic metasiltstone, fine-grained metasandstone and dolomite marble.
Talladega Group; Lay Dam Formation (Silurian?-Devonian): Lay Dam Formation (Talladega Group) - interbedded dark-green phyllite, medium-gray to light-brown and black metasiltstone, dark-green feldspathic metagraywacke, and light-gray and dark-gray medium to coarse-grained arkosic quartzite and metaconglomerate; graphitic phyllite common in upper part. In Cleburne and Calhoun Counties, rocks mapped as the Lay Dam include the Abel Gap Formation of Bearce (1973) and consist of interbedded greenish-gray metasiltstone and quartzite, black phyllitic metasiltstone, medium-gray to greenish-gray arkosic quartzite, and dark-gray pyritic quartzite. In Clay Chounty the upper part of the Lay Dam includes black graphitic sericite phyllite and slate reportedly containing plant fossils (Erin Slate Member).

Arizona

Early Proterozoic metasedimentary rocks (Early Proterozoic): Metasedimentary rocks, mostly derived from sandstone and shale, with minor conglomerate and carbonate rock. Includes quartz-rich, mostly nonvolcanic Pinal Schist in southeastern Arizona and variably volcanic-lithic sedimentary rocks in the Yavapai and Tonto Basin supergroups in central Arizona. (1600-1800 Ma)

California

Carboniferous marine rocks, unit 6 (Northeastern Sierra Nevada) (Mississippian to Early Permian): Shale, sandstone, conglomerate, limestone, dolomite, chert, hornfels, marble, quartzite; in part pyroclastic rocks
Jurassic marine rocks, unit 1 (Western Sierra Nevada and Western Klamath Mountains) (Triassic to Late Jurassic): Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks
Jurassic marine rocks, unit 5 (Northern Sierra Nevada and Eastern Klamath Mountains) (Devonian to Late Jurassic): Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks
Paleozoic marine rocks, undivided, unit 2 (Northern Mojave Desert and Southeastern Sierra Nevada) (Cambrian to Jurassic): Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite
Paleozoic marine rocks, undivided, unit 6 (Northwestern Sierra Nevada) (Permian(?) to Jurassic(?)): Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite
Permian marine sedimentary rocks, unit 3 (Northeastern Sierra Nevada) (Early to Late Permian): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks
pre-Cenozoic metasedimentary and metavolcanic rocks undivided (Early Proterozoic to Cretaceous): Undivided pre-Cenozoic metasedimentary and metavolcanic rocks of great variety. Mostly slate, quartzite, hornfels, chert, phyllite, mylonite, schist, gneiss, and minor marble.
Schist of various types and ages, unit 5 (Slate Range) (Mesozoic): Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.
Silurian and/or Ordovician marine rocks, unit 2 (Bishop) (Late Cambrian(?) to Early Permian(?)): Sandstone, shale, conglomerate, chert, slate, quartzite, hornfels, marble, dolomite, phyllite; some greenstone
Silurian and/or Ordovician marine rocks, unit 4 (Northern Sierra Nevada) (Ordovician to Devonian): Sandstone, shale, conglomerate, chert, slate, quartzite, hornfels, marble, dolomite, phyllite; some greenstone
Triassic marine rocks, unit 3 (Lake Almanor) (Permian to Jurassic): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks
Triassic marine rocks, unit 5 (Northern Sierra Nevada) (Middle to Late Triassic): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks
Triassic marine rocks, unit 6 (Southern Sierra Nevada) (Late Triassic to Early Jurassic): Shale, conglomerate, limestone and dolomite, sandstone, slate, hornfels, quartzite; minor pyroclastic rocks

Colorado

Uncompahgre Fm (Proterozoic | Paleoproterozoic Mesoproterozoic): Quartzite, slate, and phyllite

Georgia

Chickamauga Group; Middle Ordovician rocks; Rockmart Slate (Middle Ordovician): Chickamauga Group; Middle Ordovician rocks; Rockmart Slate
Slate/ Quartzite/ Conglomerate (Precambrian-Paleozoic): Slate/ Quartzite/ Conglomerate

Iowa

Sioux Quartzite (Proterozoic | Mesoproterozoic): Pink-colored fine grains of quartz sand cemented to non-porous quartzite of silica; contains some red slate; Rb-Sr dates > 1200 M.Y.

Idaho

Limestone, slate; Upper Triassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex; (Late Triassic): Upper Triassic shale overlying reefal limestone and dolomite in west-central Idaho.

Massachusetts

Coal Mine Brook Formation (Middle Pennsylvanian): Coal Mine Brook Formation - Fossiliferous, carbonaceous slate and garnet phyllite with a lens of meta-anthracite; conglomerate and arkose.
Green Lodge Formation of Rhodes and Graves (Upper Cambrian?): Green Lodge Formation of Rhodes and Graves - Quartzite and slate; contains fossils of questionable Late Cambrian age.
Hatch Hill Formation (Upper Cambrian): Hatch Hill Formation - Bluish-gray weathering black sulfidic slate and chert.
Poultney Formation (Middle and Lower Ordovician): Poultney Formation - White weathering, well-laminated gray slate and chert.
West Castleton and Nassau Formations, undivided (Lower Cambrian and Proterozoic Z): West Castleton and Nassau Formations, undivided - Dark-gray to black calcareous slate interlayered with greenish-gray phyllite.
Worcester Formation (Lower Devonian and Silurian): Worcester Formation - Carbonaceous slate and phyllite and minor metagraywacke.

Maryland

Chilhowee Group; Harpers Formation (Cambrian): Harpers Formation - Brown to dark bluish-gray banded shale, to light bluish-gray, finely laminated phyllite; distinctively pale purple in basal part; bedding obscured by cleavage; increasingly metamorphosed toward east from shale to slate and phyllite; estimated thickness 2,000 feet.
Ijamsville Formation (Late Precambrian (?)): Ijamsville Formation - Blue, green, or purple phyllite and phyllitic slate, with interbedded metasiltstone and metagraywacke; flattened pumiceous blebs occur locally.
Ijamsville Formation and Marburg Schist (Late Precambrian (?)): Ijamsville Formation - Blue, green, or purple phyllite and phyllitic slate, with interbedded metasiltstone and metagraywacke; flattened pumiceous blebs occur locally; and Marburg Schist - Bluish-gray to silvery-green, fine-grained, muscovite-chlorite-albite-quartz schist; intensely cleaved and closely folded; contains interbedded quartzites.
Libertytown Metarhyolite (Late Precambrian (?)): Libertytown Metarhyolite - Purple, bluish-black, and red, dense, fine-grained metarhyolite with feldspar phenocrysts; interbedded with blue and purple amygdaloidal metaandesite; both rhyolite and andesite interbedded with blue, purple, and green phyllitic slates.
Metarhyolite and Aasociated Pyroclastic Sediments (Late Precambrian): Metarhyolite and Assoicated Pyroclastic Sediments - Metarhyolite - Dense, blue, cryptocrystalline, with white feldspar phenocrysts and glassy quartz; red porphyritic metarhyolite at contact with Catoctin Metabasalt; and Pyroclastic sediments - tuff breccia, blue slaty tuff, white tuffaceous sericitic schist, and banded green slate.
Peach Bottom Slate (Ordovician (?)): Peach Bottom Slate - Hard, bluish-black graphitic slate; thin beds of fine-grained black quartzite near base; apparent maximum thickness 1,000 feet.
Silver Run Limestone (Late Precambrian (?)): Silver Run Limestone - Blue, thin-bedded, finely crystalline schistose limestone and calcareous slate.
Sugarloaf Mountain Quartzite (Late Precambrian (?)): Sugarloaf Mountain Quartzite - Massive white quartzite interbedded with softer sericitic quartzite, slate, and phyllite.
Swift Run Formation (Late Precambrian): Swift Run Formation - Sericitic quartzite and phyllite; blue and green tuffaceous slate with sericitic blebs; some white marble with interbedded phyllite.

Maine

Devonian Ironbound Mountain Formation (Devonian): Devonian Ironbound Mountain Formation
Devonian Matagamon Sandstone (Devonian): Devonian Matagamon Sandstone
Devonian - Ordovician Flume Ridge Formation (Devonian - Ordovician): Devonian - Ordovician Flume Ridge Formation
Devonian Tarratine Formation (Devonian): Devonian Tarratine Formation
Devonian Tarratine Formation McKenny Pond Limestone (Devonian): Devonian Tarratine Formation McKenny Pond Limestone
Devonian Tomhegan Formation (Devonian): Devonian Tomhegan Formation
Ordovician Belle Lake Slate (Ordovician): Ordovician Belle Lake Slate
Ordovician - Cambrian Chase Brook Formation (Ordovician - Cambrian): Ordovician - Cambrian Chase Brook Formation
Ordovician - Cambrian Cookson formation (Ordovician - Cambrian): Ordovician - Cambrian Cookson formation
Ordovician - Cambrian Dead River formation (Ordovician - Cambrian): Ordovician - Cambrian Dead River formation
Ordovician Chandler Ridge Formation (Ordovician): Ordovician Chandler Ridge Formation
Ordovician Chase lake formation (Ordovician): Ordovician Chase lake formation
Ordovician Chase Lake Formation sandstone and pelite member (Ordovician): Ordovician Chase Lake Formation sandstone and pelite member
Ordovician - Precambrian Z Cape Elizabeth Formation (Ordovician - Precambrian Z): Ordovician - Precambrian Z Cape Elizabeth Formation
Ordovician sandstone and pelite of the Depot Mountain sequence (Ordovician): Ordovician sandstone and pelite of the Depot Mountain sequence
Penobscot Formation (Ordovician - Cambrian): Penobscot Formation
Silurian Capens Formation (Silurian): Silurian Capens Formation
Silurian Hardwood Mountain Formation (Silurian): Silurian Hardwood Mountain Formation
Silurian - Ordovician Aroostook River Formation (Silurian - Ordovician): Silurian - Ordovician Aroostook River Formation
Silurian - Ordovician Carys Mills Formation (Silurian - Ordovician): Silurian - Ordovician Carys Mills Formation
Silurian - Ordovician Carys Mills Formation lower member (Silurian - Ordovician): Silurian - Ordovician Carys Mills Formation lower member
Silurian - Ordovician Frontenac Formation (Silurian - Ordovician): Silurian - Ordovician Frontenac Formation
Silurian - Ordovician Lobster Lake Formation (Silurian - Ordovician): Silurian - Ordovician Lobster Lake Formation
Silurian - Precambrian Z Berwick Formation (Silurian - Precambrian Z): Silurian - Precambrian Z Berwick Formation
Silurian Smyrna Mills Formation (Silurian): Silurian Smyrna Mills Formation
Silurian undifferentiated pelites and sandstones (Silurian): Silurian undifferentiated pelites and sandstones, in part of the Allsbury Formation and in part unnamed
Silurian Waterville Formation (Silurian): Silurian Waterville Formation
Silurian Waterville Formation limestone member (Silurian): Silurian Waterville Formation limestone member

Michigan

Baraga Group; Copps Formation (Early Proterozoic): Baraga Group; Copps Formation - Fine- to medium-grained graywacke and less abundant gray to black slate. Thin basal conglomerate west of Lake Gogebic contains clasts of underlying Archean rocks in a quartzitic and argillaceous matrix.
Baraga Group; Michigamme Formation; Gray to black slate (Early Proterozoic): Baraga Group; Michigamme Formation; Gray to black slate - Strongly cleaved. Represents lower stratigraphic part of formation
Chocolay Group, undivided (Early Proterozoic): Chocolay Group, undivided - In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation
Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite (Early Proterozoic): Menominee Group; Composite unit of Siamo Slate and Ajibik Quartzite - Siamo Slate is laminated green siltstone and argillite. Ajibik Quartzite is white, buff, and pink orthoquartzite and less abundant sericite quartzite.
Menominee Group; Hemlock Formation (Early Proterozoic): Menominee Group; Hemlock Formation - Predominantly mafic to intermediate volcanic flows and pyroclastic rocks with interlayered slate and tuff beds
Menominee Group; Ironwood Iron-formation (Early Proterozoic): Menominee Group; Ironwood Iron-formation - Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate
Menominee Group, undivided (Early Proterozoic): Menominee Group, undivided - Includes Negaunee Iron-formation, Siamo Slate, and Ajibik Quartzite in areas where units are too thin to map individually.
Menominee Group; unexposed magnetic unit (Early Proterozoic): Menominee Group; unexposed magnetic unit- Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).
Metagraywacke (Late Archean) (Late Archean): Metagraywacke (Late Archean) - Gray, fine-grained, thin- to thick-bedded, commonly graded graywacke and slate in Marenisco, Mich. area
Paint River Group; Lower part (Early Proterozoic): Paint River Group; Lower part - Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group
Paint River Group; Upper part (Early Proterozoic): Paint River Group; Upper part - Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

Minnesota

Little Falls Formation; Quartz-rich slate, argillite, and schist in the northwestward extent of the unit and coarse-grained megacrystic garnet-staurolite-schist in the southwestward extent (Early Proterozoic): Little Falls Formation; Quartz-rich slate, argillite, and schist in the northwestward extent of the unit and coarse-grained megacrystic garnet-staurolite-schist in the southwestward extent - Unit as an uncertain stratigraphic position relative to other Paleoproterozoic stratified units but is apparently younger than the Mille Lacs and North Range Groups.
Metasedimentary rocks, undivided (Late Archean): Metasedimentary rocks, undivided - Graywacke, slate, local units of conglomerate, arenite, graphitic slate, fine-grained felsic volcanogenic, and volcaniclastic rocks, lean oxide iron-formation and its metamorphic equivalents. Includes the Knife Lake Group and the Lake Vermilion Formation in northeastern Minnesota.
Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Graphitic schist, slate, and silicate iron-formation metamorphosed to the lower greenschist facies and related conditions (Early Proterozoic): Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Graphitic schist, slate, and silicate iron-formation metamorphosed to the lower greenschist facies and related conditions - Includes substantial quantities of mafic to intermediate igneous rocks
Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Slate, argillite, and metasiltstone metamorphosed to the lower greenschist facies (Early Proterozoic): Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Slate, argillite, and metasiltstone metamorphosed to the lower greenschist facies - Includes lesser amounts of mafic hypabyssal intrusions, and fragmental mafic volcanic rocks
Mille Lacs Group and related rocks of the Penokean fold-and-thrust bets; Graphitic schist, phyllite and slate interbedded on a fine scale (Early Proterozoic): Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Graphitic schist, phyllite and slate interbedded on a fine scale

North Carolina

Blowing Rock Gneiss (Middle Proterozoic): Blowing Rock Gneiss (1000 my) - unconformity; abundant white potassic feldspar megacrysts in finely banded biotite schist, locally calcareous; interlayered with quartz-feldspar schist, calcareous biotite schist, phyllite, black slate, calcareous quartzite, sulfidic greenstone, and siliceous tuff.
Chilhowee Group, Grandfather Mountain Formation; Meta-arkose (Late Proterozoic): Meta-arkose - sericitic, conglomeratic, locally cross-bedded; interlayered metasiltstone and slate.
Chilhowee Group; Lower Chilhowee (Cambrian): Lower Chilhowee - feldspathic quartzite, white to yellowish gray. Minor silty slate, feldspathic metasiltstone, and metaconglomerate in lower part.
Chilhowee Group; Upper Chilhowee (Cambrian): Upper Chilhowee - vitreous quartzite, white to light gray; interbedded sandy metasiltstone and slate.
Mineral Bluff Formation (Late Proterozoic): Mineral Bluff Formation - quartz-chlorite-sericite schist and phyllite with thin quartzite layers and minor interbedded graphitic schist, garnet-mica schist, staurolite schist, cross-biotite schist, and dark slate.
Mount Rogers Formation; Metagraywacke (Late Proterozoic): Metagraywacke - interlayered with metaconglomerate, laminated metasiltstone, and slate; minor calcareous metasandstone, greenstone, and metarhyolite.
Murphy Marble, Andrews Formation, and Nottely Quartzite, undivided (Late Proterozoic): Murphy Marble, Andrews Formation, and Nottely Quartzite, undivided - Murphy Marble: calcareous to dolomitic; Andrews Formation: calcareous cross-biotite schist; Nottely Quartzite: meta-orthoquartzite with slate.
Nantahala Formation and Tusquitee Quartzite, undivided (Late Proterozoic): Nantahala Formation and Tusquitee Quartzite, undivided - Nantahala Formation: slate and metasiltstone, dark gray, laminated to thin bedded, sulfidic; Tusquitee Quartzite: white to light yellowish gray, numerous, thin slate layers.
Ocoee Supergroup, Great Smokey Group; Anakeesta Formation (Late Proterozoic): Anakeesta Formation - slate to schist, dark gray, graphitic and sulfidic; includes interbedded argillaceous, feldspathic metagraywacke.
Ocoee Supergroup, Great Smokey Group; Boyd Gap Formation (Late Proterozoic): Boyd Gap Formation - dark gray, highly-sulfidic slate and metasiltstone interbedded and gradational with metagraywacke. Stratigraphic position uncertain. In Cherokee County includes upper part of Buck Bald Formation.
Ocoee Supergroup, Great Smokey Group; Copperhill Formation (Late Proterozoic): Copperhill Formation - metagraywacke, massive, graded bedding common; includes dark-gray slate, mica schist, and nodular calc-silicate rock.
Ocoee Supergroup, Great Smokey Group; Slate of Copperhill Formation (Late Proterozoic): Slate of Copperhill Formation - slate to phyllite, dark gray, graphitic, sulfidic; includes metagraywacke with local graded bedding.
Ocoee Supergroup; Great Smokey Group, undivided (Late Proterozoic): Great Smokey Group, undivided - thick metasedimentary sequence of massive to graded beds of metagraywacke and metasiltstone with interbedded graphitic and sulfidic slate and schist.
Ocoee Supergroup, Great Smokey Group; Wehutty Formation (Late Proterozoic): Wehutty Formation - slate to schist, dark gray, graphitic and sulfidic; includes mica schist, metagraywacke, and metaconglomerate.
Ocoee Supergroup, Snowbird Group; Longarm Quartzite (Late Proterozoic): Longarm Quartzite - cross-bedded, feldspathic, locally conglomeratic; includes dark slate and metasiltstone.
Ocoee Supergroup, Snowbird Group; Wading Branch Formation (Late Proterozoic): Wading Branch Formation - sandy slate to coarse-grained pebbly metagraywacke with local graded bedding. Basal quartz-sericite schist or phyllite.
Ocoee Supergroup, Walden Creek Group; Sandsuck Formation (Late Proterozoic): Sandsuck Formation - slate and metasiltstone, dark green to black. Metaconglomerate lentils in upper part; calcareous metasandstone, sandy metalimestone, and quartzite in lower part.
Ocoee Supergroup; Walden Creek Group, undivided (Late Proterozoic): Walden Creek Group, undivided - slate to metasiltstone, locally limy beds and pods; interbedded with quartz-pebble metaconglomerate and metasandstone.

New Hampshire

Frontenac Formation, undivided (Silurian?): Frontenac Formation, undivided - Interbedded thick feldspathic wackes, tan and green slates, and minor calcareous lenses.
Gile Mountain Formation, Interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone (Lower Devonian): Interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone - Contains minor marble and quartzite. Resembles Waits River Formation in Vermont.
Gile Mountain Formation, undivided (Lower Devonian): Gile Mountain Formation, undivided - Gray to tan metawacke and schist or phyllite; gradational into Meetinghouse Slate Member but more thickly bedded and less pelitic than the member. Includes minor metavolcanic lentils.
Hurricane Mountain Formation (Upper Cambrian?): Hurricane Mountain Formation - Rusty-weathered, dark siliceous scaly slate or schist of flaser structure, polymictic fragments from a few mm to (in Maine) several hundred meters. A melange consisting of metasedimentary, felsic/mafic metavolcanics, and ultramafic rocks..
Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire (Lower Devonian): Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire - Thickly bedded feldspathic volcaniclastic grit and interbedded gray slate. Equivalent to Grenier Ponds Member of the Ironbound Mountain Formation in western Maine.
Partridge Formation, undivided (Middle - Upper Ordovician): Partridge Formation, undivided - Black, rusty-weathering sulfidic-graphitic slate or schist and sparse to abundant metagraywacke. Lies stratigraphically between upper and lower parts of the Ammonoosuc Volcanics.

New Jersey

Bushkill Member (Middle Ordovician): Bushkill Member (Drake and Epstein, 1967) - Interbedded medium- to dark gray, thinly laminated to thick-bedded shale and slate and less abundant medium-gray to brownish-gray, laminated to thin-bedded siltstone. To the southwest, fine-grained, thin dolomite lenses occur near base. Complete turbidite sequences (Bouma, 1962) occur locally, but basal cutout sequences (Tbcde, Tcde or Tde) dominate. Conformable lower contact is placed at top of highest shaly limestone; elsewhere, lower contact is commonly strain slipped. Correlates with graptolite Climacograptus bicornis to Corynoides americanus zones of Riva (1969, 1974) (Parris and Cruikshank, 1992). Thickness ranges from 1,250 m (4,100 ft) in Delaware River Valley to 457 m (1,500 ft) at New York State line.
Martinsburg Formation, undivided (Upper and Middle Ordovician): Martinsburg Formation, undivided (Bayley and others, 1914) - Interbedded light-olive-gray, greenish-gray-, or dark-yellowish-brown- weathering, medium-dark- to dark-gray, laminated to medium-bedded graywacke and siltstone and olive-gray- to dark-yellowish-brown-weathering, medium-dark- to dark-gray slate. Turbidite cycles are common. Mapped only east of Lafayette and west of Lake Grinnell where thickness is at least 305 m (1000 ft).
Ramseyburg Member (Upper and Middle Ordovician): Ramseyburg Member (Drake and Epstein, 1967) - Interbedded medium- to dark-gray, to brownish-gray, fine- to medium-grained, thin- to thick-bedded graywacke sandstone and siltstone and medium- to dark-gray, laminated to thin-bedded shale and slate. Unit may form complete turbidite sequences, Tabcde (Bouma, 1962), but basal cutout sequences Tcde dominate. Basal scour, sole marks, and soft-sediment distortion of beds are common in graywacke. Thermally metamorphosed near intrusive bodies. Lower contact placed at bottom of lowest thick- to very thick bedded graywacke, but contact locally grades through sequence of dominantly thin-bedded shale and slate and minor thin- to medium-bedded discontinuous and lenticular graywacke beds in the Bushkill member. Parris and Cruikshank (1992) correlate unit with Orthograptus ruedemanni to lowest part of Climacograptus spiniferus zones of Riva (1969, 1974). Thickness ranges from 640 m (2,100 ft) in Delaware River Valley, to 1,524 m (5,000 ft) near Stillwater, to 1067 m (3,500 ft) at New York State line.

New York

Mettawee Slate (Cambrian ?): Mettawee Slate - north of 43 degrees includes Castleton (North Brittain) Conglomerate. Mudd Pond Quartzite, Zion Hill Quartzite, and Bomoseen Graywacke Members.
Mettawee Slate (Cambrian?): Mettawee Slate (Bull in Vermont) - includes Castleton (North Brittain) Conglomerate. Mudd Pond Quartzite, Zion Hill Quartzite, and Bomoseen Graywacke Members.
Mount Merino and Indian River Formations (Ordovician): Mount Merino and Indian River Formations - shale, slate, cherts.
Mount Merino and Indian River Formations (Ordovician): Mount Merino and Indian River Formations - shale, slate, cherts.
Nassau Formation (Cambrian ?): Nassau Formation - south of 43 degrees; slate, shale, thin quartzite, includes Stuyvesant Conglomerate, Diamond Rock Quartzite, Curtis Mountain Quartzite, and Bomoseen Graywacke Members.
Poultney Formation ("B" and "C" Members) (Ordovician): Poultney Formation ("B" and "C" Members) - shale, slate, siltstone.
Poultney Formation ("B" and "C" Members) (Ordovician): Poultney Formation ("B" and "C" Members) - north of Troy; shale, slate, siltstone.
Walloomsac Formation (Middle Ordovician): Walloomsac Formation - slate, phyllite, schist, metagraywacke.

Oregon

Sedimentary and volcanic rocks, partly metamorphosed (Triassic and Permian) (Permian to Triassic): Complexly folded, locally highly foliated and recrystallized undifferentiated sedimentary and volcanic rocks that in places are lithologically similar to Jurassic and Triassic rocks in the Aldrich Mountains of the Blue Mountains province and in other places resemble Elkhorn Ridge Argillite, Clover Creek Greenstone, and Burnt River Schist (Gilluly, 1937). Age probably mostly Late Permian to Late Triassic, but, as shown, may include some Early Jurassic rocks
Sedimentary rocks (Jurassic) (Late Jurassic ): Black and gray mudstone, shale, siltstone, graywacke, andesitic to dacitic water-laid tuff, porcelaneous tuff, and minor interlayers and lenses of limestone and fine-grained sediments metamorphosed to phyllite or slate. Locally includes some felsite, andesite and basalt flows, breccia, and agglomerate. Marine invertebrate fauna indicates age range from Early Jurassic (Hettangian) to early Late Jurassic (Oxfordian). In Klamath Mountains of southwest Oregon, includes Galice Formation (Wells and Peck, 1961) and unnamed, hornblende- and (or) pyroxene-bearing clastic rocks of Jurassic age (Smith and others, 1982)

Pennsylvania

Chickies Formation (Cambrian): Chickies Formation - Light-gray, hard, massive, Scolithus-bearing quartzite and quartz schist; thin, interbedded dark slate at top; conglomerate (Hellam Member) at base.
Martinsburg Formation (Ordovician): Martinsburg Formation - Gray to dark-gray shale and slate.
Peach Bottom Slate and Cardiff Conglomerate, undivided (Probably lower Paleozoic): Peach Bottom Slate and Cardiff Conglomerate, undivided - Bluish-black slate (Peach Bottom); quartz conglomerate having a matrix of sericite and chlorite (Cardiff).
Weverton and Loudoun Formations, undivided (Cambrian): Weverton and Loudoun Formations, undivided - In descending order: Weverton--gray to purplish-gray quartzite and quartzose conglomerate containing rounded pebbles. Loudoun--sericitic slate and purplish-gray, crumbly, poorly sorted, arkosic sandstone and conglomerate.

Rhode Island

Narragansett Bay Group - Pondville Conglomerate (Pennsylvanian): Narragansett Bay Group - Pondville Conglomerate - Gray to greenish conglomerate with sand-sized matrix, interbedded with quartz arenite and litharenite; typically lenticular and discontinuous. At type locality (Pondville Station, Massachusetts), unit consists of interbedded red and green slate, siltstone, arkose, and quartzite-pebble conglomerate.
Newport Group - Newport Neck Formation (Late Proterozoic? or older?): Newport Group - Newport Neck Formation - Sequences of gray, green, and maroon graded rocks, ranging from fine-grained feldspathic granule-conglomerate to maroon slate.
Pirate Cove Formation (Cambrian): Pirate Cove Formation - Pink to buff-white, thinly laminated marble units (~ 3 m thick) containing diagnostic hyoliths, interlayered with magenta slate. The basal marble varies from pink to red to orange, whereas the overlying 15-m-thick phyllite varies from maroon and red to green, gray and silver. Intimately associated spatially with OCAcj, such that the two units are grouped together at the presented map scale.

South Dakota

Metamorphosed Shale (Proterozoic | Paleoproterozoic): Gray to dark-gray phylite, slate, and mica schist. Estimated thickness at least 5,000 ft (1,524 m).
Metamorphosed Siltstone (Proterozoic | Paleoproterozoic): Medium-gray to dark-greenish-gray phyllite, slate, and biotite schist containing minor chert and amphibolite. Locally intruded by thin metagabbro sills. Thickness 1,000-3,000 ft (305-914 m).

Tennessee

Great Smoky Group, includes Unnamed Sandstone Unit, Anakeesta Formation, Thunderhead Sandstone, and Elkmont Sandstone (Precambrian): Great Smoky Group - Characterized by very massive layers of coarse graywacke and arkose. The formations at right have been mapped only in region of the Great Smoky Mountains. Thickness 14,000 to about 25,000 feet; includes Unnamed Sandstone Unit - Gray, coarse sandstone and fine conglomerate, similar to Thunderhead Sandstone. Thickness about 4,500 feet; Anakeesta Formation - Dark-gray, bluish-gray, and black slate with dark-gray interbeds of fine-grained sandstone. Thickness 3,000 to 4,500 feet; Thunderhead Sandstone - Coarse, gray feldspathic sandstone, graywacke, and conglomerate; occurs in massive ledges; graded bedding and blue quartz characteristic. Thickness 5,500 to 6,300 feet; Elkmont Sandstone - Coarse to fine, gray feldspathic sandstone, graywacke, and fine conglomerate; generally finer grained beds in lower part; graded bedding typical. Thickness 1,000 to 8,000 feet.
Great Smoky Group, including Anakeesta Formation, Thunderhead Sandstone, and Elkmont Sandstone (Precambrian): Great Smoky Group - Characterized by very massive layers of coarse graywacke and arkose. The formations have been mapped only in the region of the Great Smoky Mountains. Near Ducktown, in ascending order, the Copperhill, Hughes Gap, Hothouse, and Dean Formations are recognized. Thickness 14,000 to about 40,000 feet. Includes Anakeesta Formation - Dark-gray, bluish-gray, and black slate with dark-gray interbeds of fine-grained sandstone. Thickness 3,000 to 4,500 feet; Thunderhead Sandstone - Coarse, gray feldspathic sandstone, graywacke, and conglomerate; occurs in massive ledges; graded bedding and blue quartz characteristic. Thickness 5,500 to 6,300 feet; Elkmont Sandstone - Coarse to fine, gray feldspathic sandstone, graywacke, and fine conglomerate; generally finer grained beds in lower part; graded bedding typical. Thickness 1,000 to 8,000 feet
Ocoee Supergroup, including Walden Creek Group, (including Sandsuck Formation, Wilhite Formation, Shields Formation, Licklog Formation), Cades Sandstone, and Rich Butt Sandstone (Precambrian): Ocoee Supergroup - Terrigenous clastic sedimentary rocks, for the most part poorly sorted and coarse. The groups are subdivided into formations only in the region of the Great Smoky Mountains. Thickness as much as 50,000 feet. Includes Walden Creek Group - The formations, other than the Sandsuck, have been mapped only in the region of the Great Smoky Mountains. Thickness about 8,000 feet; Sandsuck Formation - Olive-green and gray, argillaceous, micaceous shale with coarse feldspathic sandstone and quartz- pebble conglomerate. Thickness about 2,000 feet; Wilhite Formation - Gray to green siltstone and slate with interbeds of pebble conglomerate, sandstone, and quartzite. Thickness about 4,000 feet; Shields Formation - Massive conglomerate, sandstone, argillaceous slate; conglomerate (pebbles of various rock types) characteristic. Thickness about 1,500 feet; Licklog Formation - Feldspathic sandstone, greenish phyllite, and bluish-gray slate. Thickness about 1,500 feet; and the Cades Sandstone - Gray, well-bedded, fine- to medium-grained feldspathic metasandstone, with interbeds of dark slate and metasiltstone; precise stratigraphic position unknown. Thickness about 1,500 feet; and Rich Butt Sandstone - Gray, massive beds of feldspathic, fine- to medium-grained sandstone, with interbeds of dark slate and arkosic conglomerate; exact stratigraphic position unknown. Thickness about 1,500 feet.
Rich Butt Sandstone (Precambrian): Rich Butt Sandstone - Gray, massive beds of feldspathic, fine- to medium-grained sandstone, with interbeds of dark slate and arkosic conglomerate; exact stratigraphic position unknown. Thickness about 1,500 feet.
Snowbird Group, including Pigeon Siltstone, Roaring Fork Sandstone, Metcalf Phyllite, Longarm Quartzite, and Wading Branch Formation (Precambrian): Snowbird Group - The formations at right are applicable chiefly in the area of the Great Smoky Mountains. Thickness 13,000 to about 20,000 feet. Includes Pigeon Siltstone - Laminated, greenish quartzose and feldspathic siltstone; minor fine-grained gray sandstone. Thickness as much as 10,000 feet; Roaring Fork Sandstone - Interbedded massive feldspathic sandstone, greenish siltstone, and greenish phyllite. Maximum thickness 7,000 feet; Metcalf Phyllite - Lustrous, pale-green and silvery sericitic and chloritic phyllite; siltstone interbeds abundant. Thickness uncertain; at least 5,000 feet; Longarm Quartzite - Feldspathic quartzite and arkose, conspicuously light-colored, current bedded and crossbedded. Thickness about 5,000 feet; Wading Branch Formation - Medium- to dark-gray sandy slate to coarse, pebbly feldspathic sandstone and graywacke; basal part is quartz-sericite phyllite; graded bedding common. Thickness about 1,500 feet.
Walden Creek Group, including Sandsuck Formation, Wilhite Formation, Shields Formation, and Licklog Formation (Cambrian): Walden Creek Group - The formations, other than the Sandsuck, are applicable mainly in the region of the Great Smoky Mountains. Thickness about 8,000 feet, Includes Sandsuck Formation - Olive-green and gray, argillaceous, micaceous shale with coarse feldspathic sandstone and quartz- pebble conglomerate. Thickness about 2,000 feet; Wilhite Formation - Gray to green siltstone and slate with interbeds of pebble conglomerate, sandstone, and quartzite. Thickness about 4,000 feet; Shields Formation - Massive conglomerate, sandstone, argillaceous slate; conglomerate (pebbles of various rock types) characteristic. Thickness about 1,500 feet.; Licklog Formation - Feldspathic sandstone, greenish phyllite, and bluish-gray slate. Thickness about 1,500 feet.
Walden Creek Group, including Sandsuck Formation, Wilhite Formation, Shields Formation, and Licklog Formation (Precambrian): The formations, other than the Sandsuck, have been mapped only in the region of the Great Smoky Mountains. Thickness about 8,000 feet. Includes Sandsuck Formation - Olive-green and gray, argillaceous, micaceous shale with coarse feldspathic sandstone and quartz- pebble conglomerate. Thickness about 2,000 feet; Wilhite Formation - Gray to green siltstone and slate with interbeds of pebble conglomerate, sandstone, and quartzite. Thickness about 4,000 feet; Shields Formation - Massive conglomerate, sandstone, argillaceous slate; conglomerate (pebbles of various rock types) characteristic. Thickness about 1,500 feet; Licklog Formation - Feldspathic sandstone, greenish phyllite, and bluish-gray slate. Thickness about 1,500 feet.

Texas

Carrizo Mountain Group showing metasedimentary rocks (preCambrian-Proterozoic): Carrizo Mountain Group showing metasedimentary rocks

Virginia

Aaron Slate (Proterozoic Z): Aaron Slate - Phyllite and slate.
Arvonia Formation - Slate and porphyroblastic schist (Ordovician): Arvonia Formation - Slate and porphyroblastic schist
Everona Limestone (Cambrian): Everona Limestone - Limestone.
Lynchburg Group; Charlottesville Formation (Proterozoic Z): Lynchburg Group; Charlottesville Formation - Graphitic metasiltstone, feldspathic metasandstone, and quartzite.
Lynchburg Group; Graphitic phyllite and metasiltstone (Proterozoic Z): Lynchburg Group - Graphitic phyllite and metasiltstone
Quantico Formation - Slate and porphyroblastic schist (Ordovician): Quantico Formation - Slate and porphyroblastic schist
Swift Run Formation (Proterozoic Z): Swift Run Formation - Phyllite, metasandstone, and metaconglomerate.

Vermont

Albee Formation (Ordovician): Albee Formation - Massive, gray, white-weathered quartzite and feldspathic quartzite interbedded with greenish-gray slate, phyllite, feldspthic phyllite and quartzose argillaceous phyllite. Micaceous quartzite, quartz-mica schist, mica schist and hornfels contining porphyroblasts of biotite, garnet, staurolite and sillimanite in the vicinity of granitic plutons. Soda-rhyolite tuff occurs locally. Micaceous quartzite characterized by thin, schistose "pinstripe" partings is common in many areas.
Bridgeman Hill Formation (Cambrian): Bridgeman Hill Formation - Undifferentiated dolomite, slate, and conglomerate, on east limb of St. Albans synclinorium, about equivalent to Dunham, Parker, Rugg Brook, and Saxe Brook Formations.
Gile Mountain Formation, Meetinghouse Slate Member (Devonian): Gile Mountain Formation, Meetinghouse Slate Member - Chiefly gray slate or phyllite characterized by beds of gray schistose quartzite 1/8 inch to 3 inches thick. Gile Mountain Formation and its Meetinghouse Slate Member were previously considered to be Early Devonian based on Emsian plant fossils from Compton Formation of QUE (Hueber and others, 1990; Hatch, 1991). Age assignment here changed to Early Devonian(?) because recent mapping indicates that Gile Mountain and Compton are not coextensive across VT-QUE border as formerly believed by Doll and others (1961, State map) and St. Julien and Slivitsky (1987). Instead, the formations are separated by Ironbound Mountain Formation. Ironbound Mountain Formation is conformably overlain by Compton, but it is not yet known whether Ironbound Mountain is overlain or underlain by Gile Mountain; this is shown by queried Ironbound Mountain-Gile Mountain contact in area of Averill 7.5-min quad, VT. Correlation of Gile Mountain and Compton is justified only if Gile Mountain in this area conclusively is shown to be underlain by Ironbound Mountain; otherwise, Gile Mountain (with possible exception of its Meetinghouse Slate Member) would be coeval with Silurian Frontenac Formation. Hatch (1988) proposed that Meetinghouse represents upper part of Gile Mountain on basis of graded bedding seen south of map area. This relationship is not proven, however, because Gile Mountain-Meetinghouse contact is difficult to define and graded beds are not always easily interpreted. On this map, Meetinghouse is tentatively shown to occur below main body of Gile Mountain on basis of remarkable similarity between it and Ironbound Mountain Formation. This relationship easily explains highly pelitic character of the Meetinghouse with upward-coarsening character of Lower Devonian sequences elsewhere in map area. Meetinghouse Slate Member includes volcanic facies (Moench and others, 1995).
Hatch Hill and West Castleton Formations, Undifferentiated (Cambrian): Hatch Hill and West Castleton Formations, Undifferentiated - The Hatch Hill, a relatively thin formation that succeeds the West Castleton, is characterized by rusty and spongy weathered gray calcareous quartzite traversed by numerous white-quartz viens. The West Castleton is a gray to black, siliceous, carbonaceous, and pyritiferous slate containing paper-thin white sandy laminae. Black slates are common to both formations. A blue-gray weathered black limestone is near the base of the West Castleton in a few places.
Highgate Formation (Ordovician): Highgate Formation - Banded blue limestone and calcareous slate; local lenses of limestone conglomerate; on west limb of St. Albans synclinorium.
Hortonville Formation (Ordovician): Hortonville Formation - Black, carbonaceous and pyritic slate and phyllite, locally sandy; brown weathered limy beds are common near base. Occurs east of Highgate Springs, Champlain, and Orwell thrusts.
Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated (Ordovician): Hortonville, or Cumberland Head, and Glens Falls Formations, Undifferentiated - Hortonville or Cumberland Head is combined with Glens Falls where the boundary with the Glens Falls is widely covered by surficial deposits, also where the Cumberland Head thins.
Littleton Formation (Devonian): Littleton Formation - Gray slate and phyllite containing interbeds of gray schistose quartzite 1/4 inch to 6 inches thick. West of Guildhall are lustrous, light to dark gray biotite-garnet phyllite and schist, some slate, and subordinate quartzite and impure quartzite. South of Bellows Falls gray phyllite passes eastward into gray mica schist containing porphyroblasts of biotite, garnet, and staurolite.
Missisquoi Formation (Ordovician): Missisquoi Formation - Carbonaceous phyllite and slate, black to light gray (where extensive enough to show on map).
Missisquoi Formation, Cram Hill Member (Ordovician): Missisquoi Formation, Cram Hill Member - Pale greenish-gray to black phyllite grades locally into gray to black slate; felsic to mafic volcanic rocks.
Missisquoi Formation, Umbrella Hill Member (Ordovician): Missisquoi Formation, Umbrella Hill Member - Quartz and slate pebble phyllitic conglomerate with interbeds of slate and phyllite - chiefly quartz-sericite-magnetite-chloritoid rocks.
Morses Line Formation (Ordovician): Morses Line Formation - Calcareous and non-calcareous slate; local lenses of thin-bedded limestone, limestone conglomerate, and dolomite; in St. Albans synclinorium.
Mount Hamilton Formation (Ordovician): Mount Hamilton Formation - White weatherd black, gray, green, purple, and red hard slates, some interbedded with thin cherty appearing quartzites and ribbon limestones a few vinches apart; smooth, soft, red slate; beds of ankeritic quartzite a few inches to several feet thick, locally containg layers of edgewise conglomerate; and a polymict limestone conglomerate. Lithic features vary laterally and are in many places indistinguishable from those of the underlying Hatch Hill and West Castleton Formations.
Northfield Formation (Devonian - Silurian): Northfield Formation - Dark gray to black quartz-sericite slate or phyllite with fairly widely-spaced interbeds a few inches thick of siltstone and silty crystalline limestone like that of the Waits River Formation; calcareous slate north of Lamoille River; phyllite passes into gray quartz-sericite schist containing abundant porphyroblasts of biotite and garnet in southern Vermont.
Parker Slate (Cambrian): Parker Slate - Gray to black micaceous shale and slate, includes dolomite, sandstone, and quartzite lenses; chiefly on west limb of St. Albans synclinorium.
Partridge Formation (Ordovician): Partridge Formation - Dull gray to sooty black carbonaceous slate and phyllite; mostly fissile, but locally massive and tough. Contains a few beds of both schistose and massive soda-rhyolite tuff (not shown on map). (Northeastern Vermont).
Pawlet Formation (Ordovician): Pawlet Formation - Silver gray to jet black, locally carbonaceous and pyritiferous, micaceous silty slate; interbedded, at intervals of a few inches to tens of feet, by beds of dark gray rusty weathered graywacke a few inches to 6 feet thick. The graywacke contains subangular grains of quartz, and less abundant feldspar and slate fragments, in a gray argillaceous matrix that is locally calcareous.
St. Catherine Formation (Cambrian): St. Catherine Formation - Purple, gray-green, and variegated slate and phyllite containing minor interbeds of white to green quartzite; locally albitic. Purple and green chloritoid-bearing slate and phyllite is within dashed line in northern Taconic Range, but not separated farther south.
Sweetsburg Formation (Cambrian): Sweetsburg Formation - Black, carbonaceous, well-cleaved slate with characteristic thin (1-5 mm) whitish silty bedding laminae; in St Albans and Hinesburg synclinoria and Cambridge syncline.
Sweetsburg Formation, Hungerford Slate Member (Cambrian): Sweetsburg Formation, Hungerford Slate Member - Black slate.
Sweetsburg Formation, Skeels Corners Slate and Mill River Conglomerate Members Undifferentiated (Cambrian): Sweetsburg Formation, Skeels Corners Slate and Mill River Conglomerate Members Undifferentiated - Black slate; local dolomite, sandstone, dolomite conglomerate, limestone bioherm, limestone, and calcareous shale. The Mill River is a basal limestone conglomerate.
Sweetsburg Formation, St. Albans Slate Member (Cambrian): Sweetsburg Formation, St. Albans Slate Member - Black, gray-black, or tan micaceous slate.
Waits River Formation, Ayers Cliff Member (Devonian): Waits River Formation, Ayers Cliff Member - Siliceous crystalline limestone containing thin beds of slate and phyllite north of the Lamoille River.

Washington

Cambrian quartzite (Cambrian): Gritstone with conglomerate in lower part and gray, white, and buff platy quartzite in upper part grading upward into phyllite; northern Pend Oreille County. Light-gray, platy, medium- to thick-bedded quartzite in upper part and darker impure quartzite with some interbedded argillite or phyllite in lower part; north-central Stevens County. White, gray, and reddish, medium- to thick-bedded quartzite in lower part and thin interbeds of quartzite and argillite in upper part, with very low Lower Cambrian fossils (Nevadia, Hyolthellus, and three genera of brachipods) near base of upper part; Addy district of central Stevens County. Thick argillite and thin quartzite units form an uppermost zone in southwestern Stevens County. Conspicuous phyllite units near base in north-central Lincoln County.
Carboniferous-Permian sedimentary and volcanic rocks (Devonian to Permian; some Jurassic): Sedimentary and volcanic rocks, undivided. Cherty and slaty argillite, siltstone, graywacke, chert, greenstone, tuff, andesite, and spilitic volcanics.
Carboniferous-Permian sedimentary and volcanic rocks (Devonian to Permian, minor Mesozoic): Predominantly sedimentary rocks. Graywacke, argillite, and slate; includes minor marble, siltstone, arkose, conglomerate, ribbon cherts, and volcanic rocks. Some Devonian rocks may be included in northwestern Washington.
Mesozoic-Tertiary marine rocks, undivided (Miocene to Eocene): Dark-gray, massive to poorly bedded gray-wacke of the interior Olympic Peninsula; commonly with interbedded slate, argillite, volcanic rocks, and minor arkosic sandstone. Includes rocks both older and younger than Ev2, some of which may be Paleozoic.
Middle Jurassic volcanic rocks (Middle Jurassic): Andesite, dacite, and minor basalt with slate and graywacke interbeds in the Nooksack River region of Whatcom County.
Ordovician rocks (Middle Ordovician): Mainly black to gray slate or slaty argillite, argillite, black to dark-gray siltstone in north-central Stevens County and grayish olive-green silty argillite in west-central Stevens County. Many occurrences of Early and Middle Ordovician graptolites; also rare conodonts.
Permian rocks (Permian-Triassic): Conglomerate, graywacke, siltstone, argillite and interbedded fossiliferous limestone, greenstone, and minor angular conglomerate in northwestern Stevens and Ferry Counties. Impure quartzite, sandstone, graywacke, greenstone, ribbon chert, chert breccia, and limestone in Snohomish County and on San Juan Island. Lower Permian limestone on Black Mountain in northwestern Whatcom County. Middle Permian rocks in northeastern Washington.
Pre-Middle Jurassic volcanic rocks, undivided (Early Cretaceous-Late Jurassic): Predominantly greenstone and spilitic volcanic rocks; includes some slate, argillite, and graywacke.
Pre-Tertiary metamorphic rocks, undivided (Probably Permian): Schist, gneiss, marble, quartzite, amphibolite, greenstone, metaconglomerate, graywacke; includes metasedimentary, volcanic, and intrusive rocks. Some areas, as on San Juan Islands, show little if any metamorphism.
Pre-Upper Jurassic metamorphic rocks of the low-grade zone (Jurassic): Greenschist, phyllite, and slate; includes some limestone, quartzose phyllite, schistose metaconglomerate, breccia, and basic igneous rocks. Includes schist locally.
Silurian-Devonian rocks (Silurian-Devonian): Mainly black argillite; some limestone, thin beds of conglomerate, sandstone, quartzite, and dolomite. Rocks confined to northwestern Pend Oreille County and adjacent Stevens County. Silurian age based on Monograptus and corals of several unusual genera; Devonian age based on coral fauna.
Triassic sedimentary rocks, undivided (Triassic with Permian where impossible to differentiate): Predominantly limestone, marble, and dolomite near Riverside in Okanogan County. Conglomerate, shale, graywacke, gritstone, and limestone on San Juan Island. Siltstone with greenstone locally on Orcas Island. Graywacke conglomerate, cherty greenstone, and limestone in northern Ferry County.
Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Jurassic-Early Cretaceous): Predominantly sedimentary rocks. Graywacke, argillite, and siltstone with some slate and phyllite; includes graywacke breccia and ribbon chert with minor local limestone lenses and basalt flows.
Upper Jurassic-Lower Cretaceous sedimentary and volcanic rocks (Late Cretaceous-Jurassic): Sedimentary and volcanic rocks, undivided. Graywacke, argillite, siltstone, slate, volcanic rocks, phyllite, greenschist, and greenstone.

Wisconsin

Chocolay Group, undivided (Early Proterozoic): Chocolay Group, undivided - In Dickinson County, Mich., includes Randville Dolomite, Sturgeon Quartzite, and Fern Creek Formation. In Marquette range, between Marquette Bay and Champion, includes Wewe Slate, Kona Dolomite, Mesnard Quartzite, and Enchantment Lake Formation
Menominee Group; Ironwood Iron-formation (Early Proterozoic): Menominee Group; Ironwood Iron-formation- Interbedded cherty and slaty iron-formation. Locally, secondary enrichment has formed "soft ore" bodies. In eastern part of Gogebic Range, Ironwood Iron-formation is intercalated with pyroclastic rocks of Emperor Volcanic Complex, and in eastern half of T. 47 N., R. 43 W. (where mapped within unit Xip) consists entirely of black slate
Menominee Group; unexposed magnetic unit (Early Proterozoic): Menominee Group; unexposed magnetic unit - Surrounds gneiss domes in Gogebic County, Mich. and Vilas County, Wisc., and occurs in north-central Dickinson County. Probably correlative with part of Blair Creek Formation (unit Xbc). Previously correlated with uppermost unit of Blair Creek Formation (Sims and others, 1984).
Paint River Group; Lower part (Early Proterozoic): Paint River Group; Lower part- Includes Stambaugh Formation, Hiawatha Graywacke, Riverton Iron-formation, and Dunn Creek Slate (James and others, 1968). Correlated with lower part of Baraga Group
Paint River Group; Upper part (Early Proterozoic): Paint River Group; Upper part - Dominantly Fortune Lakes Slate, but includes other rocks in poorly exposed areas. Correlated with upper part of Baraga Group.

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