USGS Home
Contact USGS
Search USGS

Mineral Resources > Online Spatial Data > Geology > by state

Geologic units containing metavolcanic rock

Arizona

Cretaceous to Late Jurassic sedimentary rocks with minor volcanic rocks (Late Jurassic to Cretaceous)

Sandstone and conglomerate, rarely forms prominent outcrops; massive conglomerate is typical near base of unit and locally in upper part. These deposits are nonmarine except in southeastern Arizona, where prominent gray marine limestone (Mural Limestone) forms the middle of the Bisbee Group. Sandstones are typically medium-bedded, drab brown, lithic-feldspathic arenites. Includes Bisbee Group (largely Early Cretaceous) and related rocks, Temporal, Bathtub, and Sand Wells formations, rocks of Gu Achi, McCoy Mountains Formation, and Upper Cretaceous Fort Crittenden Formation and equivalent rocks. (80-160 Ma)

Early Proterozoic metavolcanic rocks (Early Proterozoic)

Weakly to strongly metamorphosed volcanic rocks. Protoliths include basalt, andesite, dacite, and rhyolite deposited as lava or tuff, related sedimentary rock, and shallow intrusive rock. These rocks, widely exposed in several belts in central Arizona, include metavolcanic rocks in the Yavapai and Tonto Basin supergroups. (1650 to 1800 Ma)

Jurassic sedimentary and volcanic rocks (Jurassic)

Sandstone and conglomerate derived from volcanic rocks with associated intermediate-composition lava flows, breccias, and tuffs. In southern Arizona this unit includes rocks of the Artesa sequence, Pitoikam Formation, Mulberry Wash volcanics, Rudolfo Red Beds, Recreation Red Beds, and Gardner Canyon Formation. In western Arizona it includes the Harquar Formation, rocks of Slumgullion, and related(?) unnamed units in the Kofa and Middle Mountains. This unit is characterized by maroon, brown, and purplish-gray volcanic-lithic sandstone and siltstone, with subordinate to abundant conglomerate, quartz-rich sandstone and sparse limestone. (150-170 Ma)

Jurassic to Cambrian metamorphosed sedimentary rocks (Cambrian to Jurassic)

Highly faulted and folded rocks of units Jv, J_, and Pz, deformed and metamorphosed in Jurassic, Cretaceous and Tertiary time. This unit is restricted to west-central Arizona. (160-540 Ma)

Jurassic volcanic rocks (Jurassic)

Massive quartz-feldspar porphyry, generally interpreted as thick, welded rhyolitic tuffs, with locally abundant lava, and sandstone and conglomerate derived from volcanic rocks. Rare eolian quartzite units are interbedded in southern Arizona. Includes Ali Molina Formation, Mount Wrightson Formation, part of the Canelo Hills Volcanics, Cobre Ridge tuff, Black Rock volcanics, Planet Volcanics, and equivalent rocks. (160-200 Ma)

California

Franciscan schist (Early Cretaceous)

Blueschist and semi-schist of Franciscan complex

Paleozoic marine rocks, undivided, unit 5 (Northeastern Sierra Nevada) (Ordovician to Jurassic)

Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite

Paleozoic metavolcanic rocks, unit 4 (Western Sierra Nevada Foothills) (Paleozoic or Mesozoic)

Undivided Paleozoic metavolcanic rocks. Mostly flows, breccia and tuff, including greenstone, diabase, and pillow lavas; minor interbedded sedimentary rocks

Precambrian rocks, undivided, unit 1 (Death Valley) (Early Proterozoic to Mesozoic)

Conglomerate, shale, sandstone, limestone, dolomite, marble, gneiss, hornfels, and quartzite; may be Paleozoic in part

pre-Cenozoic granitic and metamorphic rocks undivided (Early Proterozoic to Late Cretaceous)

Granitic and metamorphic rocks, mostly gneiss and other metamorphic rocks injected by granitic rocks. Mesozoic to Precambrian.

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 1 (Peninsular Ranges) (Triassic(?))

Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian

Schist of various types and ages, unit 3 (Santa Cruz Island) (Jurassic)

Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.

Connecticut

Collinsville Formation (Middle Ordovician)

Collinsville Formation - Mixture of rock types as described for the two members; in many areas felsic and mafic striped metavolcanic rocks predominate.

Gneiss (metavolcanic) member [of Brimfield Schist] (Upper? and Middle Ordovician)

Gneiss (metavolcanic) member [of Brimfield Schist] - Medium-gray, medium-grained, layered gneiss and schist, composed of oligoclase, quartz, and biotite; some gneiss and most schist layers contain garnet and sillimanite; some gneiss layers contain garnet, hornblende or pyroxene or grade into amphibolite or calc-silicate rock. Probably includes metavolcanic rocks.

Lower part [of Maltby Lakes Metavolcanics] (Middle? Ordovician)

Lower part [of Maltby Lakes Metavolcanics] - Gray-green to green, fine-grained, generally well foliated greenschist, greenstone, and schist or phyllite, composed of albite and chlorite, plus quartz and sericite or epidote and actinolite. Mixed metavolcanics and metasedimentary rocks.

Taine Mountain and Collinsville Formations undivided (Middle to Lower? Ordovician)

Taine Mountain and Collinsville Formations undivided - see Ot and Oc.

Upper part [of Maltby Lakes Metavolcanics] (Middle? Ordovician)

Upper part [of Maltby Lakes Metavolcanics] - Green to gray-green, fine-grained, layered and foliated to massive greenstone and greenschist, composed of epidote, albite, actinolite, and chlorite, and locally minor quartz, sericite, garnet, pyrite, or calcite. Mainly metavolcanic.

Georgia

Meta-argillite/ Sericite phyllite/ Metavolcanics (Precambrian-Paleozoic)

Meta-argillite/ Sericite phyllite/ Metavolcanics

Metadacite (Precambrian-Paleozoic)

Metadacite

Undifferentiated Metavolcanics/ Sericite phyllite/ Meta-argillite/ Quartz mica schist (Precambrian-Paleozoic)

Undifferentiated Metavolcanics/ Sericite phyllite/ Meta-argillite/ Quartz mica schist

Idaho

Metavolcanic and metasedimentary rocks, diorite, trondhjemite, and migmatite; Cretaceous to Jurassic quartz dioritic plutons in Mesozoic to Permian greenschist-facies rocks; western Idaho, Blue Mountains island-arc complex (Cretaceous to Permian)

Triassic and possibly Permian submarine metavolcanic rocks of west-central Idaho.

Quartz diorite, metasedimentary rock, metavolcanic rock, and migmatite; Cretaceous to Jurassic plutons in Triassic to Permian metamorphic host rocks, undivided; western Idaho (Cretaceous to Permian)

Mixed, highly altered and migmatitic rocks; derived from imbrication and dynamic events

Quartzite, siltstone, conglomerate, and metavolcanic rocks; Late and Middle Proterozoic, undivided; Atlanta batholith roof pendants (Late and Middle Proterozoic, undivided)

Precambrian, high-grade metamorphic rock

Shale, arenite, conglomerate, intermediate and felsic volcanic rocks; Late Proterozoic rifted continental margin; southeastern Idaho (Late Proterozoic)

Younger Precambrian volcanic and diamictic units of central and southeastern Idaho.

Massachusetts

Blackstone Group (Proterozoic Z)

Blackstone Group - Undivided - Quartzite, schist, phyllite, marble, and metavolcanic rocks.

Diorite and gabbro (Proterozoic Z)

Diorite and gabbro - Complex of diorite and gabbro, subordinate metavolcanic rocks and intrusive granite and granodiorite.

Metamorphosed mafic to felsic flow, and volcaniclastic and hypabyssal intrusive rocks (Proterozoic Z)

Metamorphosed mafic to felsic flow, and volcaniclastic and hypabyssal intrusive rocks - Includes some diorite and gabbro north and northwest of Boston.

Reubens Hill Formation (Silurian or Ordovician)

Reubens Hill Formation - Amphibolite, hornblende-chlorite schist, and feldspathic schist. Includes metamorphosed diorite.

Washington Gneiss (Proterozoic Y)

Washington Gneiss - Rusty-weathering, muscovite-biotite-sillimanite and/or kyanite-garnet schist; blue-quartz ribbed conglomerate, interlayered garnet-plagioclase-quartz metadacite.

Maryland

Volcanic Complex of Cecil County (Late Precambrian (?))

Volcanic Complex of Cecil County - Metamorphosed andesitic and dacitic volcanic rocks (greenstone, greenschist, quartz amphibolite, and schistose felsite); amygdules and volcano-clastic textures locally preserved; thickness unknown.

Maine

Ordovician - Precambrian Z metasedimentary and metavolcanic rocks of the Passagassawakeag block (Ordovician - Precambrian Z)

Ordovician - Precambrian Z metasedimentary and metavolcanic rocks of the Passagassawakeag block

Ordovician - Precambrian Z Spring Point Formation (Ordovician - Precambrian Z)

Ordovician - Precambrian Z Spring Point Formation

Precambrian Z Rye Formation (Precambrian)

Precambrian Z Rye Formation

Michigan

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member (Early Proterozoic)

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member - Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Baraga Group; Volcanic-sedimentary unit (Early Proterozoic)

Baraga Group; Volcanic-sedimentary unit - Interlayered fine- to medium-grained metasedimentary rocks and metavolcanic rocks in poorly exposed areas in southern Baraga County, Mich.

Menominee and Chocolay Groups, undivided (Early Proterozoic)

Menominee and Chocolay Groups, undivided - Mapped where units are too thin to show separately on map

Menominee Group; Emperor Volcanic Complex (Early Proterozoic)

Menominee Group; Emperor Volcanic Complex - Metamorphosed intermediate to mafic pyroclastic and flow rocks in easternmost part of Gogebic Range

Minnesota

Denham Formation (Early Proterozoic)

Denham Formation - Quartz arenite and siltstone, oxide iron-formation, marble, mafic hypabyssal intrusions and fragmental volcanic rocks metamorphosed to the staurolite grade of the amphibolite facies

Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower greenschist facies (Early Proterozoic)

Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower greenschist facies - Includes fragmental volcanic rocks, mafic hypabyssal intrusions, graywacke, graphitic argillite and oxide iron-formation

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; Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower amphibolite facies (Early Proterozoic)

Mille Lacs Group and related rocks of the Penokean fold-and-thrust belt; Metabasalt, metadiabase, and metasedimentary rocks metamorphosed to lower amphibolite facies - Includes fragmental volcanic rocks, mafic hypabyssal intrusions, graphitic argillite, and oxide iron-formation

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

North Range Group; Rabbit Lake Formation (Early Proterozoic)

North Range Group; Rabbit Lake Formation - Mudstone, graywacke, iron-rich strata, and associated mafic metavolcanic rocks metamorphosed to the greenschist facies. Includes thin beds of carbonate-silicate iron-formation

North Range Group; Trommald Formation (Early Proterozoic)

North Range Group; Trommald Formation - Carbonate-silicate iron-formation overlain by hematite iron-formation and associated manganese oxide deposits. Also contains substantial quantities of volcanic and hypabyssal rocks of generally mafic composition. Metamorphosed to greenschist facies.

North Carolina

Battleground Formation (Late Proterozoic)

Battleground Formation - quartz-sericite schist with metavolcanic rock, quartz-pebble metaconglomerate, kyanite-sillimanite quartzite, and garnet-quartz rock.

Cid Formation; Felsic Metavolcanic Rock (Cambrian/Late Proterozoic)

(southwest of Asheboro); Felsic Metavolcanic Rock - metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Cid Formation; Mafic Metavolcanic Rock (Cambrian/Late Proterozoic)

(Southwest of Asheboro); Mafic Metavolcanic Rock - metamorphosed basaltic flows and tuffs, dark green to black; interbedded with felsic and intermediate metavolcanic rock and metamudstone.

Cid Formation; Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic)

(Southwest of Asheboro); Metamudstone and Meta-Argillite - thin to thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone, metaconglomerate, and metavolcanic rock.

Felsic Metavolcanic Rock (Cambrian/Late Proterozoic)

Felsic Metavolcanic Rock - metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; minor mafic and intermediate metavolcanic rock.

Felsic Metavolcanic Rock (Cambrian/Late Proterozoic)

Felsic Metavolcanic Rock - metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Felsic Metavolcanic Rock (Cambrian/Late Proterozoic)

Felsic Metavolcanic Rock - metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Floyd Church Formation; Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic)

(Southwest of Asheboro); Metamudstone and Meta-Argillite - thin to thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone, metaconglomerate, and metavolcanic rock.

Intermediate Metavolcanic Rock (Cambrian/Late Proterozoic)

Intermediate Metavolcanic Rock - metamorphosed andesitic tuffs and flows, medium to dark grayish green; minor felsic and mafic metavolcanic rock.

Intermediate Metavolcanic Rock (Cambrian/Late Proterozoic)

Intermediate Metavolcanic Rock - metamorphosed andesitic tuffs and flows, medium to dark grayish green; minor felsic and mafic metavolcanic rock.

Mafic Metavolcanic Rock (Cambrian/Late Proterozoic)

Mafic Metavolcanic Rock - metamorphosed basaltic flows and tuffs, dark green to black; interbedded with felsic and intermediate metavolcanic rock and metamudstone.

Mafic Metavolcanic Rock (Cambrian/Late Proterozoic)

Mafic Metavolcanic Rock - metamorphosed basaltic flows and tuffs, dark green to black; interbedded with felsic and intermediate metavolcanic rock and metamudstone.

Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic)

Metamudstone and Meta-Argillite - bedding plane and axial-planar cleavage common; interbedded with metasandstone, meta-conglomerate, and metavolcanic rock.

Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic)

Metamudstone and Meta-Argillite - thin to thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone, metaconglomerate, and metavolcanic rock.

Metavolcanic-Epiclastic Rock (Cambrian/Late Proterozoic)

Metavolcanic-Epiclastic Rock - metamorphosed argillite, mudstone, volcanic sandstone, conglomerate, and volcanic rock.

Metavolcanic-Epiclastic Rock (Cambrian/Late Proterozoic)

Metavolcanic-Epiclastic Rock - metamorphosed argillite, mudstone, volcanic sandstone, and conglomerate, and volcanic rock.

Metavolcanic Rock (Cambrian/Late Proterozoic)

Metavolcanic Rock - interbedded felsic to mafic tuffs and flowrock.

Phyllite and Schist (Cambrian/Late Proterozoic)

Phyllite and Schist - locally laminated and pyritic; includes phyllonite, sheared fine-grained metasediment, and metavolcanic rock. In Lilesville granite aureole, includes hornfels.

Phyllite and Schist (Cambrian/Late Proterozoic)

Phyllite and Schist - minor biotite and pyrite; includes phyllonite, sheared fine-grained metasediment and metavolcanic rock.

Phyllite and Schist (Cambrian/Late Proterozoic)

Phyllite and Schist - minor biotite and pyrite; includes phyllonite, sheared fine-grained metasediment and metavolcanic rock.

Tillery Formation; Metamudstone and Meta-Argillite (Cambrian/Late Proterozoic)

(Southwest of Asheboro); Metamudstone and Meta-Argillite - thin to thick bedded; bedding plane and axial-planar cleavage common; interbedded with metasandstone, metaconglomerate, and metavolcanic rock.

Uwharrie Formation; Felsic Metavolcanic Rock (Cambrian/Late Proterozoic)

(at Asheboro and to south); Felsic Metavolcanic Rock - metamorphosed dacitic to rhyolitic flows and tuffs, light gray to greenish gray; interbedded with mafic and intermediate metavolcanic rock, meta-argillite, and metamudstone.

Volcanic Metaconglomerate (Cambrian/Late Proterozoic)

Volcanic Metaconglomerate - includes metagraywacke and metamudstone.

Yadkin Formation (Cambrian/Late Proterozoic)

Yadkin Formation - metamorphosed graywacke, volcanic sandstone, and siltstone; interbedded with mafic and intermediate metavolcanic flows and tuffs.

New Hampshire

Aziscohos Formation, Lower unnamed member (Upper Cambrian? - Lower Ordovician?)

Aziscohos Formation, Lower unnamed member - Rusty, dark metapelite containing thin coticule laminations, feldspathic metatuff, and vein quartz lenses.

Frontenac Formation, Mixed volcanic and sedimentary facies (Silurian?)

Frontenac Formation, Mixed volcanic and sedimentary facies.

Frontenac Formation, Proximal bimodal volcanic facies (Silurian?)

Frontenac Formation, Proximal bimodal volcanic facies.

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.

Littleton Formation, Epiclastic metavolcanic sediments (Lower Devonian)

Littleton Formation, Epiclastic metavolcanic sediments.

Littleton Formation, Lower unnamed member (Lower Devonian)

Littleton Formation, Lower unnamed member - Thinly or poorly bedded aluminous lower part, somewhat rusty. Rare quartzite lentils. Carrabassett Formation in northwestern Maine is probably correlative.

Littleton Formation, undivided (Lower Devonian; Siegenian)

Littleton Formation undivided - Gray metapelite and metawacke and subordinate metavolcanic rocks; generally, but not everywhere, conformable with underlying Fitch or Madrid Formations. Fossiliferous in western New Hampshire.

Massabesic Gneiss Complex (Late Proterozoic)

Massabesic Gneiss Complex - Migmatite consisting of pink, foliated biotite granite intruding gneissic and granulose metasedimentary and metavolcanic rocks in southeastern New Hampshire.

Metamorphosed gabbro, diorite, and intrusive basalt dikes (Devonian? - Silurian?)

Metamorphosed gabbro, diorite, and intrusive basalt dikes - Chiefly in northern New Hampshire.

Metavolcanic and metasedimentary rocks of the lower part of Ammonoosuc Volcanics, undivided (Middle Ordovician)

Metavolcanic and metasedimentary rocks of the lower part of Ammonoosuc Volcanics, undivided.

Partridge Formation, Interstratified metavolcanic rocks (Middle - Upper Ordovician)

Partridge Formation, Interstratified metavolcanic rocks - Chiefly amphibolites, found in southwestern New Hampshire.

Perry Mountain and Rangeley Formations, undivided (Silurian)

Perry Mountain and Rangeley Formations, undivided.

Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon (Lower?- Middle? Silurian)

Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon.

Rangeley Formation, undivided (Lower Silurian (Llandoverian))

Rangeley Formation, undivided.

Rye Complex (Ordovician? - Late Proterozoic?)

Rye Complex - Migmatite of gray, foliated, sheared or mylonitized two-mica granite and pegmatite, minor hornblende-biotite diorite, intruding metapelites and metavolcanic rocks in southeastern New Hampshire.

Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments (Upper to Middle Silurian (Ludlovian and Wenlockian))

Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments.

Nevada

Conglomerate, limestone, meta-andesite, phyllite, and shale (Devonian to Mississippian)

CONGLOMERATE, LIMESTONE, META-ANDESITE, PHYLLITE, AND SHALE-Includes Grossman, Banner, Nelson, and Mountain City Formation. Northern Elko County

Havallah sequence of Silberling and Roberts (1962) (Mississippian to Permian)

HAVALLAH SEQUENCE OF SILBERLING AND ROBERTS (1962)-Chert, argillite, shale, greenstone, and minor amounts of siltstone, sandstone, conglomerate, and limestone. Includes Schoonover Formation of Fagan (1962) and Reservation Hill Formation in Elko County, Farrel Canyon Formation in southwestern Humboldt County, Havallah and Pumpernickel Formations in Pershing, Lander, and parts of Humboldt Counties, and rocks originally considered a part of the Pablo and Excelsior Formations in northern Nye, northern Esmeralda, and southern Mineral Counties. Assignment of some rocks to the Havallah sequence in the East Range, Pershing County, is highly uncertain. Includes rocks ranging in age from Late Mississippian to Early Permian

Siliceous and volcanic rocks (Mississippian)

SILICEOUS AND VOLCANIC ROCKS-In Humboldt County, consists of altered pillow lavas, coarse volcanic breccias, clastic limestone, and minor amounts of sandstone, shale, siliceous shale, and chert of the Goughs Canyon Formation (Lower and Upper Mississippian). In the East Range, Pershing County, consists of quartzite, conglomerate, slate, limestone, chert, and greenstone of the Inskip Formation (Mississippian?).

New York

Gabbroic or noritic metanorthosite (Middle Proterozoic)

Gabbroic or noritic metanorthosite - dark mineral content in excess of 10 percent (part of unit Ya).

Gabbroic or noritic metanorthosite (Middle Proterozoic)

Gabbroic or noritic metanorthosite - dark mineral content in excess of 10 percent (part of unit Ya).

Interlayered gabbroic or noritic metanorthosite (Middle Proterozoic)

Interlayered gabbroic or noritic metanorthosite - mangerite or charnockite, and the Yach lithology.

Metanorthosite and anorthositic gneiss (Middle Proterozoic)

Metanorthosite and anorthositic gneiss.

Metanorthosite and anorthositic gneiss (Middle Proterozoic)

Metanorthosite and anorthositic gneiss - mafic mineral percentage contoured in northwestern Marcy massif (St. Regis Quadrangle); contour value shown on high side of countoue line. See also Yach, Yack, Yamu.

Oregon

Melange of Dutchmans Peak (Triassic or Paleozoic) (Paleozoic(?) to Jurassic(?))

Heterogeneous mixture of interlayered metasedimentary and metavolcanic rocks metamorphosed to upper greenschist and (or) almandine-amphibolite facies, and serpentinite, gabbro, and metagabbro (Smith and others, 1982)

Pennsylvania

Benner Formation through Loysburg Formation, undivided (Ordovician)

Benner Formation through Loysburg Formation, undivided - In descending order: Benner Formation--light- to dark-gray, thick-bedded limestone (calcilutite); includes chemically pure Valentine Member (Obv) at top, and, below, the less pure Valley View Member, which contains metabentonite beds--all laterally equivalent to impure limestones of Oak Hall Member; Stover Member at base is dark-gray limestone (calcilutite) having dolomite streaks; Benner is called "Linden Hall" by some workers. Snyder Formation--light- to medium-gray limestone, laminated to medium-bedded; has mud cracks, oolites, and dolomitic layers. Hatter Formation--medium-gray, fossiliferous, argillaceous limestone, laminated and dolomitic. Loysburg Formation--light- to medium-gray, medium-bedded limestone (Clover Member) overlying laminated, alternating limestone, dolomitic limestone, and dolomite (Milroy ["tiger-striped"] Member).

Chambersburg Formation (Ordovician)

Chambersburg Formation - Dark-gray, cobbly, argillaceous limestone; abundant irregular shale partings; some metabentonite beds present.

Coburn Formation through Loysburg Formation, undivided (Ordovician)

Coburn Formation through Loysburg Formation, undivided - Includes, in descending order, the Coburn Formation through Nealmont Formation, undivided (Ocn) and Benner Formation through Loysburg Formation, undivided (Obl).

Coburn Formation through Nealmont Formation, undivided (Ordovician)

Coburn Formation through Nealmont Formation, undivided - In descending order: Coburn Formation--medium-gray to very dark gray, very fossiliferous limestone and shaly limestone; Salona Formation--very dark gray to black, nonfossiliferous shaly limestone and calcareous shale containing metabentonite beds; Nealmont Formation--medium-gray fossiliferous limestone (calcarenite--Rodman Member) overlying thin-bedded shaly limestone (calcilutite--Center Hall Member).

Greenstone schist (Precambrian)

Greenstone schist - Fine to medium grained, light to medium green; includes probable metavolcanic rocks.

South Carolina

Asbill Pond Formation (Middle Cambrian)

Asbill Pond Formation: metamorphosed siltstones and sandstones having interbedded felsic to mafic metavolcanic rocks

Battleground Formation, Schistose to phyllitic volcaniclastic rocks (Neoproterozoic)

Battleground Formation, Schistose to phyllitic volcaniclastic rocks

Little River Sequence, metasedimentary rocks (Cambrian or Neoproterozoic)

Little River Sequence, metasedimentary rocks: white-mica schist and phyllite, metatuff, quartz-muscovite schist, and minor quartzite

Metavolcanic and metasedimentary rocks of Bel Air Belt (Ordovician to Neoproterozoic)

Metavolcanic and metasedimentary rocks of Bel Air Belt

Persimmon Fork Formation (Cambrian to Neoproterozoic)

Persimmon Fork Formation: predominately metatuff

Virginia

Chopawamsic Formation - Interlayered felsic and mafic metavolcanic rocks (Cambrian)

Chopawamsic Formation- Interlayered felsic and mafic metavolcanic rocks

Felsic/Mafic Volcanic Rocks (Proterozoic)

Felsic/mafic volcanic rocks as exotic blocks within melange units

Hyco Formation (Proterozoic Z)

Hyco Formation - Lithic and crystal metatuff

Mafic and Felsic Volcanic Rocks (Proterozoic)

Mafic and felsic volcanic rocks

Vermont

Metadiorite (Devonian)

Metadiorite - Dikes and sills of metagabbro, metadiabase and meta-andesite too small to show are chiefly in the Missisquoi, Albee, and Orfodville formations.

Missisquoi Formation, Coburn Hill Volcanic Member (Ordovician)

Missisquoi Formation, Coburn Hill Volcanic Member - Actinolite-epidote-chlorite-albite greenstone and hornblende-albite-epidote amphibolite; includes pillow lavas.

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.

Washington

Lower and Middle Jurassic marine rocks (Devonian-Permian)

Dark-gray, massive to thick-bedded, siliceous argillite, siltstone, and shale; includes minor graywacke and limestone. Confined to northwestern Whatcom County.

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-Carboniferous crystalline complex (Devonian)

Metahornblendite, amphibolite, gneiss, metadiorite, meta-quartz diorite, and trondhjemite. As klippes along western slope of northern Cascade Mountains.

Pre-Middle Jurassic sedimentary and volcanic rocks (Late Paleozoic deposition? with Cretaceous metamorphism?)

Sedimentary and volcanic rocks, undivided. Graywacke, argillite, slate, greenstone, and spilitic volcanic rocks.

Pre-Tertiary volcanic rocks, undivided (Probably mostly Jurassic)

Andesite and basalt flows, and greenstone; includes minor interbedded limestone, arkose, quartzite, and chert beds.

Upper Jurassic-Lower Cretaceous volcanic rocks (Jurassic-Cretaceous on San Juan Islands; possibly Eocene in King County)

Predominantly volcanic rocks, mostly metamorphosed to greenstone and greenschist; includes some sedimentary rocks

Wisconsin

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member (Early Proterozoic)

Baraga Group; Michigamme Formation; Mafic to intermediate flows and pyroclastic rocks, including Clarksburg Volcanics member - Poorly exposed. Includes Clarksburg Volcanics member which is mostly mafic to intermediate pyroclastic rocks in Marquette trough, between Marquette Bay and Champion

Felsic metavolcanic rocks of 1835- to 1845-Ma age group (Early Proterozoic)

Felsic metavolcanic rocks of 1835- to 1845-Ma age group - Rhyolite to dacite and, locally, andesite tuff, breccia, and minor sedimentary rocks, including conglomerate. Exposed in central Wisconsin.

Menominee and Chocolay Groups, undivided (Early Proterozoic)

Menominee and Chocolay Groups, undivided - Mapped where units are too thin to show separately on map

Milladore Volcanic Complex (about 1860 +/- 7 Ma) (Early Proterozoic)

Milladore Volcanic Complex (about 1860 +/- 7 Ma) - Succession of poorly exposed interlayered metavolcanic and metasedimentary rocks. Lithic units described in Sims (1990)

Wyoming

Metamorphosed mafic and ultramafic rocks (Archean)

METAMORPHOSED MAFIC AND ULTRAMAFIC ROCKS. Teton Range--Rendezvous Metagabbro; 2,875 Ma or older. Gros Ventre Range--Hornblende gneiss and serpentinite. Wind River Range--Pillowed amphibolite, metagabbro, and ultramafic sills. Wind River Canyon (cutting through Owl Creek Mountains)--Amphibolite and felsic gneiss of volcanic origin. Older than 2,700 Ma. Bighorn and Granite Mountains--Amphibolite. Seminoe Mountains--Amphibolite of volcanic origin, komatiite, and metagabbro. Casper Mountain--Amphibolite and serpentinite. Laramie Mountains--Amphibolite of volcanic origin, komatiite(?), metagabbro, and ultramafic sills.

Metasedimentary and metavolcanic rocks (Proterozoic | Paleoproterozoic )

METASEDIMENTARY AND METAVOLCANIC ROCKS. Sierra Madre--Granite gneiss, felsic gneiss, amphibolite, and metavolcanic rocks. Medicine Bow Mountains--Granite gneiss, felsic gneiss, amphibolite, and hornblende gneiss. Laramie Mountains--Pelitic schist, marble, granite gneiss, layered amphibolite, and felsic gneiss. Black Hills--Pelitic schist; includes minor amounts of granite and amphibolite.

Metasedimentary and metavolcanic rocks (Archean)

METASEDIMENTARY AND METAVOLCANIC ROCKS--Amphibolite, hornblende gneiss, biotite gneiss, quartzite, iron-formation, metaconglomerate, marble, and pelitic schist; locally preserved textures and structures suggest origin to be sedimentary or volcanic. Older than 2,875 Ma in Teton Range; older than 3,200 Ma in Granite Mountains; older than 2,600 Ma in Medicine Bow Mountains and Sierra Madre, where it is the Late Archean Phantom Lake Metamorphic Suite 3.