Skip to main content

Geologic units containing Gneiss

Gneiss
A foliated rock formed by regional metamorphism, in which bands or lenticles of granular minerals alternate with bands or lenticles in which minerals having flaky or elongate prismatic habits predominate. Generally less than 50% of the minerals show preferred orientation.
This category is also used for mica gneiss.
Subtopics:
Felsic gneiss
Mafic gneiss
Migmatite
Orthogneiss
Paragneiss

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

Alabama

Motts Gneiss, Unnamed unit (Precambrian to Paleozoic)
Motts Gneiss, Unnamed unit - unnamed unit comprised of masses of epidote-hornblende-oligoclase mylonitic gneiss and amphibolite.
Mylonitic and Cataclastic Rocks in the Brevard, Towaliga, and Goat Rock Fault Zones (Precambrian to Paleozoic)
Mylonitic and Cataclastic Rocks in the Brevard, Towaliga, and Goat Rock Fault Zones - mylonite and blastomylonite; contains minor ultramylonite, mylonite schist, and mylonite gneiss.
Mylonitic and Cataclastic Rocks in the Brevard, Towaliga, and Goat Rock Fault Zones (Precambrian to Paleozoic)
Mylonitic and Cataclastic Rocks in the Brevard, Towaliga, and Goat Rock Fault Zones - blastomylonite, mylonite gneiss, locally includes mylonite schist and mylonite quartzite in Towaliga fault zone.
Poe Bridge Mountain Group (Precambrian to Paleozoic)
Poe Bridge Mountain Group - coarse to fine-grained feldspathic graphite schist, +/- staurolite +/- kyanite +/- sillimanite-muscovite-biotite schist, and garnet-biotite-muscovite schist, and gneiss; locally common pegmatites. Rocks in the area of Turkey Heaven Mountain in Cleburne and Randolph Counties that are here assigned to the Poe Bridge Mountain Group also have been interpreted as part of the Wedowee Group.
Talladega Group; Lay Dam Formation, unnamed diamictite facies (Silurian?-Devonian)
Talladega Group; Lay Dam Formation, unnamed diamictite facies - Unnamed diamictite facies of Lay Day Formation in Coosa and Chilton Counties consists of cobbles and boulders of carbonate, pelitic rocks, quartzite, chert, felsic plutonic rocks, and gneiss in a metagraywacke matrix.
Wacoochee Complex; Halawaka Schist (Precambrian to Paleozoic)
Halawaka Schist - feldspathic muscovite-biotite schist and quartz-diorite gneiss; locally contains lenses of muscovite-graphite schist and amphibolite; commonly cut by feldspathic veins and pegmatites.
Wedowee Group; Wedowee Group undifferentiated (Precambrian to Paleozoic)
Wedowee Group undifferentiated - Wedowee Group undifferentiated includes the Cragford Phyllite and Cutnose Gneiss. Cragford Phyllite -- interbedded fine-grained graphite-chlorite-sericite schist and phyllite, garnet-sericite schist and phyllite, graphite-quartz-sericite phyllite, locally feldspathic biotite gneiss, calc-silicate rock, and quartzite. Cutnose Gneiss -- cyclically interbedded fine-grained quartz-biotite feldspathic gneiss, graphite-chlorite-sericite schist, locally thin interbeds of graphite-quartz-sericite phyllite, and quartzite. Rocks in the area northeast of Clanton in Chilton and Coosa Counties that are here assigned to the Wedowee Group also have been interpreted as part of the Higgins Ferry Group.

Arizona

Early Proterozoic granitic rocks (Early Proterozoic)
Wide variety of granitic rocks, including granite, granodiorite, tonalite, quartz diorite, diorite, and gabbro. These rocks commonly are characterized by steep, northeast-striking foliation. (1600-1800 Ma)
Early Proterozoic metamorphic rocks (Early Proterozoic)
Undivided metasedimentary, metavolcanic, and gneissic rocks. (1600-1800 Ma)
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)
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)
Paleozoic sedimentary rocks (Paleozoic)
Undivided Paleozoic limestone, dolostone, quartzite, shale, and related sedimentary rocks. (248-544 Ma)
Proterozoic granitic rocks (Proterozoic)
Undivided Early and Middle Proterozoic granitic rocks (units Xg and Yg). (1400-1800 Ma)
Tertiary to Early Proterozoic gneissic rocks (Early Proterozoic to Tertiary)
Gneissic rocks with complex histories, typically with well developed, light-colored granitoid layers and dark-colored biotite- and amphibole-rich layers. Protoliths are of Tertiary to Proterozoic age. This unit includes variably mylonitic gneisses in metamorphic core complexes that have been exhumed from middle crustal levels by large-displacement middle Tertiary normal faults, and gneiss exposed at scattered locations near the Colorado River in southwestern Arizona. These rocks are interpreted to record Proterozoic, Mesozoic, and Tertiary metamorphism and deformation. (15-1800 Ma)

California

Jurassic marine rocks, unit 4 (Peninsular Ranges and Western Transverse Ranges) (Paleozoic(?) to Late Jurassic)
Shale, sandstone, minor conglomerate, chert, slate, limestone; minor pyroclastic rocks
Mesozoic granitic rocks , unit 2 (Peninsular Ranges) (Middle Jurassic to Late Cretaceous)
Mesozoic granite, quartz monzonite, granodiorite, and quartz diorite
Paleozoic marine rocks, undivided, unit 7 (Southeastern Klamath Mountains) (Devonian(?))
Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite
Precambrian granitic rocks, unit 1 (Eastern Mojave Desert) (Early Proterozoic to Miocene)
Precambrian granite, syenite, anorthosite, and gabbroic rocks in the San Gabriel Mountains; also various Precambrian plutonic rocks elsewhere in southeastern California
Precambrian igneous and metamorphic rock complex (Early Proterozoic to Miocene)
Complex of Precambrian igneous and metamorphic rocks. Mostly gneiss and schist intruded by igneous rocks; may be Mesozoic in part.
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
Precambrian rocks, undivided, unit 2 (Mojave Desert and Transverse Ranges) (Early Proterozoic to Miocene)
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 5 (Slate Range) (Mesozoic)
Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.
Schist of various types and ages, unit 9 (Cargo Muchacho Mountains) (Jurassic(?))
Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.

Connecticut

Amphibolite-bearing unit of Manhattan Schist (Cambrian?)
Amphibolite-bearing unit of Manhattan Schist - Like Manhattan Schist but with numerous lenses and layers of amphibolite.
Basal member of upper slice of Canaan Mountain Schist (Cambrian?)
Basal member of upper slice of Canaan Mountain Schist - Gray, generally rusty- or tan-weathering gneiss, composed of quartz, plagioclase, microcline, biotite, and muscovite, interlayered with feldspathic quartzite.
Beardsley Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician)
Beardsley (hornblendic) Member [of Harrison (Prospect) Gneiss] - Medium- to dark-gray, medium-grained, well-layered and lineated gneiss, composed of plagioclase, quartz, microcline, hornblende, biotite, and epidote. Microcline may occur as megacrysts 1 to 3 cm across. Minor layers of garnetiferous schist and rarely of calc-silicate rock or marble. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields crystallization ages of 428+/-2 Ma (Early Silurian) for the Pumpkin Ground and 446+/-2 Ma (Late Ordovician) for the Beardsley. Age of the Beardsley based on analysis of seven zircon and two sphene fractions. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).
Brimfield Schist (Upper? and Middle Ordovician)
Brimfield Schist (includes Hamilton Resevoir Formation) - Gray, rusty-weathering, medium- to coarse-grained, interlayered schist and gneiss, composed of oligoclase, quartz, K-feldspar, and biotite, and commonly garnet, sillimanite, graphite, and pyrrhotite. K-feldspar partly as augen 1 to 3 cm across. Minor layers and lenses of hornblende- and pyroxene-bearing gneiss, amphibolite, and calc-silicate rock.
Brimfield Schist (uncertain) (Upper? and Middle Ordovician)
Brimfield Schist (uncertain) (includes Hamilton Resevoir Formation) - Gray, rusty-weathering, medium- to coarse-grained, interlayered schist and gneiss, composed of oligoclase, quartz, K-feldspar, and biotite, and commonly garnet, sillimanite, graphite, and pyrrhotite. K-feldspar partly as augen 1 to 3 cm across. Minor layers and lenses of hornblende- and pyroxene-bearing gneiss, amphibolite, and calc-silicate rock.
Bristol Gneiss (Middle? Ordovician)
Bristol Gneiss - Light, medium-grained, massive to well-layered gneiss, composed of plagioclase, quartz, and biotite, also muscovite and garnet in many layers, interlayered in places with dark amphibolite. Bristol Member of Collinsville Formation (Stanley, 1964) is here raised in rank and revised as Bristol Gneiss in the report area. Garnet- and epidote-bearing amphibolite and hornblende gneiss assigned by Stanley to the upper part of his Bristol Member is here assigned to base of the overlying Collinsville Formation and composes the unnamed hornblende gneiss member. As defined here, the Bristol Gneiss consists of plagioclase-quartz gneiss characterized by foliae of muscovite or biotite, or locally chlorite, which in places give the unit a striking pinstriping; contains scattered small garnets and large pods of amphibolite. Average thickness may be about 2,000 ft; thickness varies due to local intense folding. Probably correlates with the Moretown Formation of central MA, in which case it would constitute a fourth member of Stanley's Taine Mountain Formation. Formational status assigned in this report based on its unique textural and lithological character. Inferred age is Middle Ordovician (Simpson, 1990).
Canterbury Gneiss (Devonian)
Canterbury Gneiss (may be equivalent to Ayer Granite of Massachusetts) - Light-gray, medium-grained, variably foliated, locally strongly lineated gneiss, composed of quartz, oligoclase, microcline, and biotite, locally also muscovite, or epidote, and generally with megacrysts 1 to 2 cm long of either or both feldspars.
Carringtons Pond Member [of Trap Falls Formation] (Middle or Lower Ordovician)
Carringtons Pond Member [of Trap Falls Formation] - Interlayered medium- to dark-gray, rusty-weathering, medium-grained schist and light-gray, fine- to medium-grained gneiss, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet; schist locally contains sillimanite or kyanite; gneiss locally contains K-feldspar; amphibolite layers common.
Collins Hill Formation (Upper? and Middle Ordovician)
Collins Hill Formation ( = Partridge Formation of New Hampshire) - Gray, rusty-weathering, medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, muscovite, biotite, and garnet, and commonly staurolite, kyanite, or sillimanite, generally graphitic, interlayered with fine-grained two-mica gneiss, especially to the west, and with calc-silicate and amphibolite layers, also rare quartz-spessartine (coticule) layers.
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.
Dalton Formation (Lower Cambrian and perhaps partly older)
Dalton Formation (including Poughquag and Lowerre Formation) - Gray, tan-weathering, medium-grained, generally well layered gneiss or feldspathic quartzite, composed of quartz, microcline, plagioclase, muscovite, biotite, and generally tourmaline; some schistose micaceous layers have sillimanite; commonly as quartz-sillimanite nodules rimmed with muscovite. Layers of purer quartzite in many areas, especially near the top or where the formation is thin.
Dioritic phase [of Preston Gabbro] (Middle Ordovician or older)
Dioritic phase [of Preston Gabbro] - Medium- to dark-gray, streaked or speckled, medium-grained diorite and quartz diorite, gneissic where sheared near contact, composed of plagioclase, hornblende, and biotite, and locally quartz and relic pyroxene.
Eastford gneiss phase [of Canterbury Gneiss] (Devonian)
Eastford gneiss phase [of Canterbury Gneiss] - Mainly light-gray, medium-grained, foliated to strongly lineated gneiss, composed of quartz, microcline, oligoclase, or albite, biotite, and muscovite.
Fly Pond (calc-silicate) Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician)
Fly Pond (calc-silicate) Member [of Tatnic Hill Formation] - Light-gray, medium-grained, layered to massive calc-silicate gneiss, composed of andesine, quartz, hornblende or actinolite, epidote, and commonly diopside, biotite, and scapolite; some layers are calcitic.
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.
Gneiss of Highlands massifs (Proterozoic Y; may contain some older rocks)
Gneiss of Highlands massifs, (including Fordham Gneiss) - Mixture of rock types described below, where not separately mapped.
Harrison Gneiss (Middle? Ordovician)
Harrison Gneiss (including Prospect Gneiss) - Interlayered dark- and light-gray, medium-grained, well-foliated gneiss, composed of andesine, quartz, hornblende, and biotite (also locally K-feldspar as megacrysts 1 to 5 cm long). Thought to be metavolcanic equivalent of unit Ob.
Harrison Gneiss (including Prospect Gneiss) (Middle? Ordovician)
Harrison Gneiss (including Prospect Gneiss) - Interlayered dark- and light-gray, medium-grained, well-foliated gneiss, composed of andesine, quartz, hornblende, and biotite (also locally K-feldspar as megacrysts 1 to 5 cm long). Thought to be metavolcanic equivalent of unit Ob. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields ages of 428+/-2 Ma for the Pumpkin Ground and 446+/-2 Ma for the Beardsley. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).
Hoosac Schist (Cambrian?)
Hoosac Schist - Light- to medium-gray, rusty-weathering, fine- to medium-grained schist and poorly layered schistose gneiss, composed of quartz, biotite, plagioclase, muscovite, and generally garnet and sillimanite or kyanite.
Hornblende gneiss and amphibolite (Proterozoic Y)
Hornblende gneiss and amphibolite - Dark-gray to mottled, fine- to medium-grained, massive to foliated amphibolite and gneiss, composed of hornblende and plagioclase, also commonly biotite and minor quartz; commonly interlayered with banded felsic gneiss. Locally contains calc-silicate rock or diopsidic calcite marble.
Joshua Rock Member [of New London Gneiss] (Proterozoic Z?)
Joshua Rock Member [of New London Gneiss] - Medium-gray (weathers with red spots of hematite), medium-grained, foliated gneiss composed of microperthite, quartz, albite, aegerine-augite, and magnetite; rare riebeckite.
Layered gneiss (Proterozoic Y)
Layered gneiss - Gray, medium-grained, well-foliated and generally well layered, light and dark, but locally wispy gneiss, composed of quartz and plagioclase, with microcline locally in the light layers and abundant biotite and common hornblende in the dark layers; garnet or epidote locally. Layers and lenses of calc-silicate rock and amphibolite in some areas.
Mamacoke Formation (Proterozoic Z?)
Mamacoke Formation - Interlayered (but layers locally indistinct) light- to dark-gray, medium-grained gneiss, composed of plagioclase, quartz, and biotite; sillimanite, garnet, hornblende, or microcline in certain layers; in upper part locally contains quartz-sillimanite nodules or thin layers of quartzite, amphibolite, or calc-silicate rock.
Manhattan Schist (Cambrian?)
Manhattan Schist (including Waramaug Formation and Canaan Mountain Schist) - Dark-gray to silvery, rusty-weathering, generally coarse grained, foliated but poorly layered to massive gneiss or schistose gneiss, composed of quartz, oligoclase, microcline, biotite, and muscovite, and generally sillimanite and garnet. Amphibolite layers locally, especially near base where in places separately mapped as unit CAma. Cambrian Manhattan Schist in this report includes four informal members: Warren member, garnetiferous biotite schist member, Shepaug member, and schistose granulite member. The Warren member occurs only in the Above All thrust sheet, the Shepaug member only in the Rabbit Hill thrust sheet. The schist member occurs in both. The granulite member occurs in the Rabbit Hill thrust sheet and the Lake Waramaug thrust sheet. The Warren includes mainly interbedded, dark-gray, muscovite-garnet-chlorite-plagioclase-biotite-quartz schist, amphibolite lenses, siliceous granulite, and finely-layered schistose gneiss. The Shepaug consists of interbedded orthoclase-garnet-plagioclase-biotite-quartz schistose gneiss, rusty-weathering, schistose gneisses and schists with sillimanite rods, and subordinate granulite beds with sillimanite nodules similar to those in the schistose granulite member (Panish, 1992).
Metavolcanic member [of Collins Hill Formation] (Upper? and Middle Ordovician)
Metavolcanic member [of Collins Hill Formation] - Ranges from mafic to felsic, from dark layered amphibolite and hornblende schist, locally with garnet or epidote, to light-gray (in places purplish), laminated gneiss, composed of quartz, oligoclase, and biotite, in which some layers contain garnet (generally manganiferous) and hornblende or cummingtonite.
Middletown Formation (Middle Ordovician)
Middletown Formation ( = Ammonoosuc Volcanics of New Hampshire) - Heterogeneously interlayered dark- to light-gray, generally medium grained gneiss and granofels, ranging from quartz-biotite gneiss through felsic amphibole gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-sillimanite nodules.
Middletown Formation (Middle Ordovician)
Middletown Formation ( = Ammonoosuc Volcanics of New Hampshire) - Heterogeneously interlayered dark- to light-gray, generally medium grained gneiss and granofels, ranging from quartz-biotite gneiss through felsic amphibole gneiss to amphibolite and characteristically containing anthophyllite or cummingtonite with or without hornblende. Also layers of calc-silicate rock and of biotite gneiss with quartz-sillimanite nodules.
Monson Gneiss (Middle or Lower Ordovician?)
Monson Gneiss (may be equivalent to part of Waterford Group) - Interlayered light to dark, mostly medium to coarse-grained gneiss and amphibolite; gneiss composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others; traces of garnet, epidote, and magnetite.
Mylonite along Paleozoic faults (Upper or Middle Paleozoic)
Mylonite along Paleozoic faults - Mylonite, blastomylonite, and blastomylonitic gneiss, composed of intensely granulated quartz, plagioclase, biotite, and epidote, in places with hornblende or microcline and commonly with secondary minerals. In places has later been silicified (compare unit Jsi)..
Nodular member [of Harrison Gneiss] (Middle? Ordovician)
Nodular member [of Harrison Gneiss] - Harrison Gneiss containing prominent quartz-sillimanite nodules.
Plainfield Formation (Proterozoic Z?)
Plainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-gray or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopsite-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules.
Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)
Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite - Plainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-gray or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopsite-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules. Potter Hill Granite Gneiss - Light-pink to gray, tan-weathering, fine- to medium-grained, rarely porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline, quartz, oligoclase (or albite), biotite, and magnetite, minor muscovite, and local garnet. Narragansett Pier Granite - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.
Plainfield Formation plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)
Plainfield Formation - Interlayered light-gray, thin-bedded quartzite, in places with feldspar, mica, graphite, or pyrite, light- to medium-gray gneiss composed of quartz, oligoclase, and biotite (rarely microcline), medium- to dark-gray schist composed of quartz, oligoclase, biotite, sillimanite, and garnet, dark-grey or green gneiss composed of plagioclase, quartz, biotite, and hornblende (commonly with diopside), amphibolite, diopside-bearing quartzite, and calc-silicate rock. In places contains quartz-sillimanite nodules. Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.
Ponaganset Gneiss (Proterozoic Z?)
Ponaganset Gneiss - Dark-gray, coarse-grained, porphyritic, well-foliated gneiss, composed of oligoclase, quartz, microcline (mostly as megacrysts up to 8 cm long), biotite, magnetite, and generally hornblende; also garnet and muscovite where hornblende is absent. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. Ponaganset lies east of the Hope Valley shear zone and extends from RI into MA. [Apparently does not occur in CT.] Predominantly granite, ranges to tonalite. Gray to light gray, some pink, generally medium- to coarse-grained, but ranges from fine-grained to porphyritic. Alkali K-feldspar, plagioclase, quartz, and biotite are major minerals. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. Strong lineation is defined by elongate aggregates of quartz and feldspar and trains of biotite and hornblende. Age is Late Proterozoic based on correlation with Northbridge Gneiss (MA), which has been dated at 557+/-4 Ma by Zartman and Naylor (1984) (Skehan and Rast, 1990).
Porphyritic member [of Southbridge Formation] (Silurian or Ordovician or both)
Porphyritic member [of Southbridge Formation] - Light- to medium-gray, fine-grained porphyritic massive to layered gneiss, composed of quartz, oligoclase, microcline, and biotite, with megacrysts 1 to 2 cm long of microcline.
Preston Gabbro plus Quinebaug Formation (Middle Ordovician or older)
Preston Gabbro plus Quinebaug Formation - Preston Gabbro - Dark, medium- to coarse-grained, mainly massive gabbro, composed of labradorite, augite, and opaques, generally with hornblende, locally hypersthene, or olivine or both. Quinebaug Formation - Medium- to dark-gray, commonly greenish, medium-grained, well-layered gneiss, composed of hornblende, andesine, biotite, and epidote, commonly with quartz or garnet, interlayered with amphibolite.
Pumpkin Ground Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician)
Pumpkin Ground (porphyritic) Member [of Harrison (Prospect) Gneiss] - Medium- to light-gray, medium- to coarse-grained, well-layered and foliated gneiss, composed of oligoclase, microcline, quartz, and biotite; some layers have numerous microcline megacrysts 1 to 5 cm across; others have hornblende. Minor layers of garnetiferous schist and gneiss. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields ages of 428+/-2 Ma (Early Silurian) for the Pumpkin Ground and 446+/-2 Ma (Late Ordovician) for the Beardsley, accepted by authors as crystallization ages. Pumpkin Ground intrudes the Trap Falls Formation. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).
Ratlum Mountain Schist plus Amphibolite unit [in Ratlum Mountain Schist] (Lower Ordovician)
Ratlum Mountain Schist plus Amphibolite unit [in Ratlum Mountain Schist] - Ratlum Mountain Schist - Gray, medium-grained, interlayered schist and granofels, composed of quartz, oligoclase, muscovite (in the schist), biotite, and garnet, also staurolite and kyanite in the schist. Numerous layers and lenses of amphibolite; also some of quartz-spessartine (coticule) and calc-silicate rock. Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician) - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine, commonly with minor quartz and magnetite, and locally with garnet, biotite, and epidote.
Rope Ferry Gneiss (Proterozoic Z?)
Rope Ferry Gneiss (may be equivalent in part to Monson Gneiss) - Interlayered (but layers commonly lenticular to indistinct) light- to dark-gray, fine- to medium-grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others; local layers of amphibolite. Rope Ferry described as locally massive, gray-colored, lenticularly layered hornblende-biotite-quartz-plagioclase gneiss. Thickness varies; averages 1,130 m. U-Pb analysis of zircon and sphene from the Rope Ferry yields a 620+/-3 Ma age. Protolith consisted primarily of mafic metavolcanic rocks. Unconformably underlies Potter Hill Granite Gneiss of Sterling Plutonic Suite (Skehan and Rast, 1990).
Rusty mica schist and gneiss (Proterozoic Y; may contain some older rocks)
Rusty mica schist and gneiss (equivalent in part to Washington Gneiss of Massachusetts) - Dark-gray, rusty-weathering, well-foliated and well- to poorly layered schist and gneiss composed of quartz, plagioclase, biotite, muscovite, sillimanite, and locally garnet; some layers of feldspathic quartzite and garnetiferous amphibolite.
Taine Mountain and Collinsville Formations undivided (Middle to Lower? Ordovician)
Taine Mountain and Collinsville Formations undivided - see Ot and Oc.
Tatnic Hill Formation (Upper? and Middle Ordovician)
Tatnic Hill Formation - Medium- to dark-gray, medium-grained gneiss or schist composed of quartz, andesine, biotite, garnet, and sillimanite, locally kyanite, muscovite, or K-feldspar, interlayered with locally mappable units and thinner layers of rusty-weathering graphitic pyrrhotitic two-mica schist, amphibolite, and calc-silicate rock.
Trap Falls Formation (Middle or Lower Ordovician)
Trap Falls Formation (may be equivalent in part to Golden Hill Schist) - Gray to silvery, partly rusty weathering, medium-grained generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered with two-mica gneiss and granulite and with amphibolite.
Trap Falls Formation plus Ordovician? granitic gneiss (Middle or Lower Ordovician)
Trap Falls Formation plus Ordovician? granitic gneiss - Trap Falls Formation (may be equivalent in part to Golden Hill Schist) - Gray to silvery, partly rusty weathering, medium-grained generally well layered schist, composed of quartz, sodic plagioclase, biotite, muscovite, and garnet, locally with sillimanite or kyanite, interlayered with two-mica gneiss and granulite and with amphibolite. Ordovician? granitic gneiss (including local terms Ansonia, Mine Hill, "Tyler Lake," "Siscowit") - White, light-gray, buff, or pink, generally foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and biotite, and locally garnet or sillimanite. Commonly contains numerous inclusions or layers of mica schist and gneiss.
Upper member [of Middletown Formation] (Middle Ordovician)
Upper member [of Middletown Formation] - Light-gray, generally rusty weathering, well-layered gneiss and granofels, composed of oligoclase, quartz, biotite, and amphibole (cummingtonite, anthophyllite, gedrite, or hornblende, or several of these), also garnet and chlorite. Many layers of amphibolite and biotite gneiss throughout.
Upper slice of Canaan Mountain Schist (Cambrian?)
Upper slice of Canaan Mountain Schist - Dark-gray to silvery, generally rusty weathering, medium- to coarse-grained, well-foliated, massive to well-layered schist and schistose gneiss, composed of quartz, plagioclase, biotite, muscovite, and generally garnet and sillimanite; also layers of amphibolite.
Waterbury Gneiss (Proterozoic Z or Cambrian or both)
Waterbury Gneiss - Medium- to dark-gray, fine- to medium-grained, generally irregularly foliated and lenticular rather than regularly layered schist and schistose gneiss, composed of biotite, quartz, oligoclase, kyanite (or sillimanite), and garnet, also locally microcline, irregularly mixed with granitoid gneiss, composed of oligoclase or andesine, quartz, biotite, and commonly microcline and muscovite.
Waterford Group (Proterozoic Z?)
Waterford Group (may be equivalent in part to Monson Gneiss) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite. Usage of Waterford Group follows Goldsmith (1980; 1985). Described as a sequence of metavolcanic and metaplutonic plagioclase gneisses and amphibolites that unconformably overlies the Plainfield Formation in the Hope Valley terrane. (Hope Valley and Esmond-Dedham terranes compose the Avalon superterrane of this report.) Thickness is variable; ranges to 3,100 m. Subdivided (ascending) into Mamacoke Formation with its upper Cohanzie Member (first used?), New London Gneiss, and Rope Ferry Gneiss. Age is Late Proterozoic based on U-Pb analyses of zircon and sphene in the Rope Ferry Gneiss (620+/-3 Ma, Wintsch and Aleinikoff, 1987) (Skehan and Rast, 1990).
Waterford Group and Branford Gneiss (Proterozoic Z?)
Waterford Group (may be equivalent in part to Monson Gneiss) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite. Branford Gneiss - Gray to white but rarely pink., medium-grained, well-foliated granitic gneiss, composed of oligoclase, K-feldspar, quartz, biotite, garnet, magnetite, and muscovite.
Waterford Group plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian)
Waterford Group plus Stony Creek Granite Gneiss plus Narragansett Pier Granite - Waterford Group (may be equivalent in part to Monson Gneiss) - Interlayered part (but layers locally distinct) of Waterford Group, light to dark, generally medium grained gneiss, composed of plagioclase, quartz, and biotite, with hornblende in some layers and microcline in others. Some layers of amphibolite. Stony Creek Granite Gneiss - Red to pink, unevenly medium to very coarse grained, variably foliated granite or granite gneiss, composed of oligoclase, K-feldspar, and quartz with minor biotite and magnetite, sporatic garnet (in foliated varieties), and local muscovite. Commonly contains granite and pegmatite of Narragansett Pier type (and probably age). In much of area both granites occur as innumerable veins penetrating other units or as larger bodies full of inclusions of those units, which can be mapped through the bodies of granite. Narragansett Pier Granite (Permian) - Pink to red, medium- to coarse-grained (commonly pegmatitic), generally massive (not gneissic) granite, composed of microcline, oligoclase, quartz, and biotite, and accessory muscovite and magnetite. Considerable associated pegmatite.

Delaware

Georgia

Amphibolite/ Epidote Quartzite/ Granite Gneiss (Precambrian-Paleozoic)
Amphibolite/ Epidote Quartzite/ Granite Gneiss
Amphibolite/ Mica Schist/ Biotitic Gneiss (Precambrian-Paleozoic)
Amphibolite/ Mica Schist/ Biotitic Gneiss
Biotite Gneiss/ Hornblende Gneiss/ Granite Gneiss (Age not given)
Biotite Gneiss/ Hornblende Gneiss/ Granite Gneiss
Epidote Quartzite/ Amphibolite/ Sericite Schist/ Biotite Granite Gneiss (Precambrian-Paleozoic)
Epidote Quartzite/ Amphibolite/ Sericite Schist/ Biotite Granite Gneiss
Garnet Mica Schist/ Gneiss (Precambrian-Paleozoic)
Garnet Mica Schist/ Gneiss
Hornblende Gneiss (Precambrian-Paleozoic)
Hornblende Gneiss
Hornblende Gneiss/ Amphibolite (Precambrian-Paleozoic)
Hornblende Gneiss/ Amphibolite
Hornblende Gneiss/ Amphibolite/ Granite Gneiss (Precambrian-Paleozoic)
Hornblende Gneiss/ Amphibolite/ Granite Gneiss
Hornblende Gneiss/ Granite Gneiss/ Biotite Gneiss (Precambrian-Paleozoic)
Hornblende Gneiss/ Granite Gneiss/ Biotite Gneiss
Metagraywacke/ Mica Schist/ Calc-silicate Gneiss (Precambrian-Paleozoic)
Metagraywacke/ Mica Schist/ Calc-silicate Gneiss
Mica Schist/ Gneiss (Precambrian-Paleozoic)
Mica Schist/ Gneiss
Mica Schist/ Gneiss/ Amphibolite (Precambrian-Paleozoic)
Mica Schist/ Gneiss/ Amphibolite
Mica Schist/ Quartzite/ Gneiss/ Amphibolite (Precambrian-Paleozoic)
Mica Schist/ Quartzite/ Gneiss/ Amphibolite
Phyllite/ Quartzite/ Calc-silicate gneiss (Precambrian-Paleozoic)
Phyllite/ Quartzite/ Calc-silicate gneiss
Quartz Mica Schist/ Hornblende Schist/ Biotitic Gneiss (Precambrian-Paleozoic)
Quartz Mica Schist/ Hornblende Schist/ Biotitic Gneiss
Sericite Schist/ Amphibolite/ Granite gneiss (Precambrian-Paleozoic)
Sericite Schist/ Amphibolite/ Granite gneiss
Sillimanite Schist/ Gneiss (Precambrian-Paleozoic)
Sillimanite Schist/ Gneiss
Sillimanite Schist/ Gneiss/ Amphibolite (Precambrian-Paleozoic)
Sillimanite Schist/ Gneiss/ Amphibolite

Iowa

Idaho

Felsic gneiss, mafic gneiss, orthogneiss, and calc-silicate rock; Early Proterozoic metamorphic rocks; central Idaho; Pioneer Mountains metamorphic core complex (Early Proterozoic)
Precambrian, high-grade metamorphic rock; metasediment subdivisions are (PC3, PC2, PC1).
Garnet-mica schist, gneiss, and quartzite; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Late to Early Proterozoic)
Precambrian high-grade metamorphic rock; metasediment; Kyanite-sillimanite-garnet-mica schist and gneiss; minor quartzite
Garnet-sillimanite-biotite gneiss, quartzite, and amphibolite; Middle Proterozoic Lemhi Group; southern Belt trans-Idaho metamorphic provinces (Middle Proterozoic)
Precambrian high-grade metamorphic rock; metasediment; kyanite-sillimanite-garnet-mica coarse-grained schist and gneiss; minor quartzite
Garnet-sillimanite-biotite schist; Middle Proterozoic Prichard Formation, northern Belt province (Early Middle Proterozoic)
Precambrian high-grade metamorphic rock; metasediment; kyanite-sillimanite-garnet-mica coarse-grained schist and gneiss; minor quartzite
Metamorphosed granitoid plutonic rocks and metasedimentary rocks, undivided; Cretaceous orthogneiss in Middle Proterozoic metasedimentary host rocks; west-central Idaho (Cretaceous to Middle Proterozoic)
Highly metamorphosed rock of central Idaho; age and origin of rock questionable.
Metamorphosed granodiorite, quartz monzonitek tonalite, quartz diorite; mostly Cretaceous orthogneiss and migmatite; northern and Atlanta batholith; margins of Bitterroot and Atlanta batholiths (Cretaceous)
Metamorphosed granitic intrusive rock; associated with pluton margins and stress areas.
Mica schist, quartzite, gneiss, and amphibolite; Late to Early Proterozoic high-grade metasedimentary rocks (subunits are ZXmhs, ZXmhq, and ZXmhc); trans-Idaho metamorphic province (Proterozoic)
Precambrian high-grade metamorphic rock; metasediment
Migmatitic paragneiss, quartzite, orthogneiss, and amphibolite; Early Proterozoic to Late Archean metamorphic rocks; northern Belt province; Settlement antiform in Priest River metamorphic core complex (Early Proterozoic to Late Archean)
Precambrian, high-grade metamorphic rock; metasediment; kyanite-sillimanite garnet-mica coarse-grained schist and gneiss; minor quartzite
Peraluminous monzogranite, granodiorite, pegmatite, aplite, and migmatite; mostly Cretaceous intrusions of the Kaniksu batholithic assemblage, but with minor Eocene intrusions, undivided; northern Idaho (Cretaceous to Eocene)
Cretaceous plutons; felsic; as granite or quartz monzonite; probably includes unmapped older and younger crystalline bodies.
Quartz diorite, tonalite, granodiorite, orthogneiss, migmatite; Cretaceous to Jurassic quartz dioritic plutons; western Idaho, Blue Mountains island-arc complex (Early Cretaceous to Late Jurassic)
Lower Cretaceous to Upper Jurassic intrusions in west-central Idaho.
Schist, quartzite, marble, skarn, and mafic gneiss; Jurassic to Mississippian amphibolite-facies rocks; southwestern Idaho, western accreted island-arc complex (Jurassic to Mississippian)
Metamorphic complex of probable Paleozoic units of southwestern Idaho.

Massachusetts

Biotite-garnet-feldspar gneiss of Ragged Hill (Devonian)
Biotite-garnet-feldspar gneiss of Ragged Hill - Although extremely narrow, shows local cross cutting relations with Ops, Sfs, and Dl.
Black and white, well-layered hornblende-biotite-plagioclase gneiss and amphibolite (Proterozoic Y)
Black and white, well-layered hornblende-biotite-plagioclase gneiss and amphibolite - Contains irregular pods of diopside or cummingtonite-talc rock or amphibole calc-silicate, epidote-layered quartz-plagioclase gneiss near Hinsdale.
Calc-silicate granofels and gneiss (Proterozoic Y)
Calc-silicate granofels and gneiss - Including calcitic or dolomitic chondrodite-diopside marble, coarse hornblende-plagioclase-diopside and diopside rock, locally containing beds of lustrous muscovite-kyanite sillimanite-garnet schist.
Cobble Mountain Formation (Middle Ordovician)
Cobble Mountain Formation - Thick-bedded (15 to 40 cm), nonrusty-weathering, silvery-gray, medium- to coarse-grained mica gneiss interlayered with nonrusty-weathering mica schist and minor amphibolite.
Cobble Mountain Formation (Middle Ordovician)
Cobble Mountain Formation - Brown- or rusty-weathering thin-bedded feldspathic gneiss and mica schist.
Cobble Mountain Formation (Middle Ordovician)
Cobble Mountain Formation - Rusty-weathering mica schist; thin (15 cm or less) beds of gneiss.
Cobble Mountain Formation (Middle Ordovician)
Cobble Mountain Formation - Light-brown, fine- to medium-grained pelitic schist and granofels locally graded in beds less than 15 cm thick. Local amphibolite. Rare calc-silicate rock, feldspar gneiss, coticule and cummingtonite schist.
Collinsville Formation (Middle Ordovician or older)
Collinsville Formation - Interlayered amphibolite and felsic gneiss in beds less than 1 m thick. Local, coarse-grained magnetite-hornblende gneiss.
Collinsville Formation (Middle Ordovician or older)
Collinsville Formation - Plagioclase gneiss and minor amphibolite.
Collinsville Formation (Middle Ordovician or older)
Collinsville Formation - Amphibolite and minor plagioclase gneiss. Magnetite-hornblende granofels near top.
Collinsville Formation (Middle Ordovician or older)
Collinsville Formation - Rusty-weathering, massive granofels containing anthophyllite and tourmaline; some rusty-stained gneiss.
Dalton Formation (Lower Cambrian and Proterozoic Z)
Dalton Formation - Well-layered orange-tan feldspathic, biotite-spotted, muscovite-microcline-quartz gneiss and granofels.
Diorite (Proterozoic Z)
Diorite - Medium-grained hornblende diorite metamorphosed in part to amphibolite and hornblende gneiss.
Granite, gneiss, and schist, undivided (Proterozoic Z)
Granite, gneiss, and schist, undivided - Plutonic and metamorphic rocks of probable Proterozoic Z age. May include plutonic and volcanic rocks of Paleozoic or younger age.
Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y)
Gray, well-layered biotite-plagioclase-quartz gneiss - Ybu may contain undifferentiated areas of Ycs, Yl, and Yhb.
Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y)
Gray, well-layered biotite-plagioclase-quartz gneiss - Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.
Hawley Formation (Middle Ordovician)
Hawley Formation - Pale-buff, light-green or white, medium-grained plagioclase gneiss. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).
Hawley Formation (Middle Ordovician)
Hawley Formation - White to very-light-green plagioclase granofels containing minor garnet. Plagioclase-hornblende-garnet gneiss containing hornblende blades and garnet megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).
Hoosac Formation (Lower Cambrian and Proterozoic Z)
Hoosac Formation - Rusty-brown to dark-gray, albite-spotted muscovite-biotite schist or gneiss, with interlayered black garnet-biotite-albite-quartz schist near base; interfingers with Dalton Formation.
Hoosac Formation (Lower Cambrian and Proterozoic Z)
Hoosac Formation - Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.
Hoosac Formation (Lower Cambrian and Proterozoic Z)
Hoosac Formation - Undifferentiated Hoosac Formation.
Intimately interfolded Littleton and Partridge Formations (Lower Devonian and Middle Ordovician)
Intimately interfolded Littleton and Partridge Formations - In areas of poor exposure and incomplete mapping.
Marlboro Formation (Ordovician, Cambrian, or Proterozoic Z)
Marlboro Formation - Thinly layered amphibolite, biotite schist and gneiss, minor calc-silicate granofels and felsic granofels.
Massabesic Gneiss Complex (Ordovician and Proterozoic Z)
Massabesic Gneiss Complex - Biotite-feldspar paragneiss of Proterozoic Z age intruded by potassium-feldspar-rich gneiss of Ordovician age.
Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z)
Monson Gneiss - Layered to massive biotite-plagioclase gneiss, amphibolite, microcline augen gneiss.
Nashoba Formation (Ordovician or Proterozoic Z)
Nashoba Formation - Sillimanite schist and gneiss, partly sulfidic, amphibolite, biotite gneiss, calc-silicate gneiss and marble. Nashoba Formation occurs in Nashoba zone of eastern MA. Consists of interlayered sillimanite-bearing, partly sulfidic schist and gneiss, calc-silicate gneiss, and subordinate quartzite and marble. Protoliths were probably volcanogenic sediments interlayered with limy marine sediments. Bell and Alvord (1976) divided Nashoba into 10 members on basis of lithology. Amphibolite is most abundant near presumed base, namely in Boxford Member. Skehan and Abu-Moustafa (1976) divided Nashoba into 30 members based on section in Wachusett-Marlborough tunnel. Although Bell and Alvord's and Skehan and Moustafa's sections contain similar lithologies, Bell and Alvord's is much thicker, and Boxford Member is not readily identified in Skehan and Abu-Moustafa's. Subdivision of Nashoba is conjectural south of Marlborough and Shrewsbury. On MA State bedrock map (Zen and others, 1983) only Boxford Member is separated out from the rest of the Nashoba because this unit was the only member clearly recognized in several area. A definite sequence of members probably does not exist anywhere in the Nashoba because of lenticularity of assemblages and repeated rock types, both of which could be accounted for by either sedimentary or tectonic processes. Although Castle (1965) considered Fish Brook to be either a premetamorphic intrusive rock or a core gneiss of intrusive or sedimentary ancestry, Bell and Alvord (1976) considered it to be volcanic or volcaniclastic in origin. Zircons in Fish Brook are certainly volcanic in origin and yield a date of 730 +/-26 Ma (Olszewski, 1980). If the rock were a core gneiss, that date would apply only to the Fish Brook and not to surrounding rocks; but, Bell and Alvord (1976) believe Fish Brook to be part of the Marlboro Formation-Nashoba Formation sequence and therefore the date does apply to the sequence. In addition, a 1500 Ma date for Shawsheen Gneiss [reference not given] helps bracket age of Marlboro-Nashoba sequence. An upper limit for the sequence was established from the 430 +/-5 Ma age of intruding Sharpers Pond Diorite and 450 +/-23 Ma age of the intruding Andover Granite (Zartman and Naylor, 1984). Although age on MA State bedrock map is shown as Proterozoic Z or Ordovician (due to uncertainty regarding actual rocks sampled by Olszewski and a strong belief that rocks of Nashoba zone correlated with Ordovician rocks to the west), author now feels that rocks of Nashoba zone (except for Tadmuck Brook Schist) are all Proterozoic, but that they are unlike the Proterozoic rocks of neighboring Milford-Dedham zone. [no formal age change made in this report] (Goldsmith, 1991).
Quinebaug Formation (Ordovician, Cambrian, or Proterozoic Z)
Quinebaug Gneiss - Amphibolite, biotite and hornblende gneiss, felsic gneiss, and calc-silicate gneiss.
Shawsheen Gneiss (Ordovician or Proterozoic Z)
Shawsheen Gneiss - Sillimanite gneiss, sulfidic at base; minor amphibolite.
Tatnic Hill Formation (Ordovician or Proterozoic Z)
Tatnic Hill Formation - Fly Pond Member - Calc-silicate gneiss and marble.
Tatnic Hill Formation (Ordovician or Proterozoic Z)
Tatnic Hill Formation - Sulfidic sillimanite schist, sillimanite schist and gneiss, biotite gneiss; minor amphibolite, calc-silicate gneiss and marble.
Undifferentiated Poplar Mountain and Dry Hill Gneisses (Proterozoic Z)
Undifferentiated Poplar Mountain and Dry Hill Gneisses .

Maryland

Baltimore Gneiss (Precambrian)
Baltimore Gneiss - Biotite-quartz-feldspar gneiss and biotite-hornblende gneiss; amphibolite widespread but subordinate; texturally varied; granitic gneiss, veined gneiss, augen gneiss, banded gneiss, and migmatite, in places complexly intermingled; age 1,1000 m.y. * by radiogenic dating. Layered paragneiss in Baltimore City southeast of Relay Quartz Diorite.
Cockeysville Marble (Late Precambrian (?))
Cockeysville Marble - Metadolomite, calc-schist, and calcite marble are predominant; calc-gneiss and calc-silicate marble widespread but minor; thickness about 750 feet.
James Run Gneiss (Late Precambrian (?))
James Run Gneiss - Thick-bedded, light gray biotite-quartz-plagioclase gneiss with thin interbeds of quartz amphibolite; grades downward into sharply layered, thin- to thick-bedded paragneiss composed of subequal amounts of biotite-quartz-plagioclase gneiss and quartz amphibolite; thickness unknown.
Setters Formation (Late Precambrian (?))
Setters Formation - Upper member: Feldspathic mica schist and mica gneiss; total thickness 200 to 500 feet. Middle member: Impure quartzite interstratified with thin beds of mica schist; total thickness 200 to 500 feet. And Lower member: Medium-grained, feldspathic mica schist; locally granitized; total thickness 200 to 500 feet.
Wissahickon Formation; Boulder Gneiss (Late Precambrian (?))
Wissahickon Formation; Boulder Gneiss - (Formerly mapped as Sykesville and Laurel Formations.) Thick-bedded to massive, pebble- and boulder-bearing, arenaceous to pelitic metamorphic rock; typically a medium-grained, garnet-oligoclase-mica-quartz gneiss; locally an intensely foliated gneiss or schist; apparent thickness 15,000 feet.

Maine

Michigan

Minnesota

North Carolina

Alligator Back Formation; Gneiss (Late Proterozoic)
Gneiss - finely laminated to thin layered; locally contains massive gneiss and micaceous granule conglomerate; includes schist, phyllite, and amphibolite.
Alligator Back Formation; Mica schist and phyllite (Late Proterozoic)
Mica schist and phyllite - laminated to thin layered; interlayered with minor biotite-muscovite gneiss and amphibolite.
Amphibolite (Cambrian/Late Proterozoic)
Amphibolite - metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, and small nonlayered masses of metadiorite and metagabbro.
Amphibolite and Biotite Gneiss (Cambrian/Late Proterozoic)
Amphibolite and Biotite Gneiss - interlayered; minor layers and lenses of hornblende gneiss, metagabbro, mica schist, and granitic rock.
Ashe Metamorphic Suite and Tallulah Falls Formation; Metagraywacke (Late Proterozoic)
Metagraywacke - foliated to massive, locally conglomeratic; interlayered and gradational with mica schist, muscovite-biotite gneiss, and rare graphitic schist.
Ashe Metamorphic Suite and Tallulah Falls Formation; Mica schist (Late Proterozoic)
Mica schist - locally sulfidic and graphitic; minor interlayered mica gneiss and amphibolite.
Ashe Metamorphic Suite and Tallulah Falls Formation; Muscovite-biotite gneiss (Late Proterozoic)
Muscovite-biotite gneiss - locally sulfidic; interlayered and gradational with mica schist, minor amphibolite, and hornblende gneiss.
Banded Gneiss (Cambrian/Late Proterozoic)
Banded Gneiss - interlayered with calc-silicate rock, metaconglomerate, amphibolite, sillimanite-mica schist, and granitic rock.
Biotite Granitic Gneiss (Middle Proterozoic)
Biotite Granitic Gneiss (950-1250 my) - unconformity; contains paragneiss and granitic to quartz monzonitic orthogneiss; locally schistose and mylonitic. Locally includes tectonic slices, infolded remnants, or recrystallized equivalents of the Grandfather Mountain Formation. Equivalent to the Wilson Creek Gneiss.
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.
Coweeta Group (Late Proterozoic)
Coweeta Group - quartz dioritic gneiss, feldspar-quartz-biotite gneiss, metasandstone and quartzite, alumino-silicate schist, garnetiferous biotite gneiss, and minor amphibolite. Quartz dioritic gneiss predominant.
Felsic Mica Gneiss (Cambrian/Late Proterozoic)
Felsic Mica Gneiss - interlayered with biotite and hornblende gneiss and schist.
Felsic Mica Gneiss (Cambrian/Late Proterozoic)
Felsic Mica Gneiss - interlayered with graphitic mica schist and mica-garnet schist, commonly with kyanite; minor hornblende gneiss.
Henderson Gneiss (Cambrian)
Henderson Gneiss (524 my) - monzonitic to granodioritic; inequigranular.
Injected Gneiss (Cambrian/Late Proterozoic)
Injected Gneiss - biotite gneiss and schist intruded by numerous sills and dikes of granite, pegmatite, and aplite; minor hornblende gneiss.
Lineated Felsic Mica Gneiss (Cambrian/Late Proterozoic)
Lineated Felsic Mica Gneiss - white to pink, with strong lineation of muscovite-biotite streaks and prismatic quartz aggregates; planar foliation and layering weak; minor mica schist and hornblende gneiss.
Mica Schist (Cambrian/Late Proterozoic)
Mica Schist - contains garnet, staurolite, kyanite, or sillimanite; includes lenses and layers of quartz schist, micaceous quartzite, biotite gneiss, amphibolite, and phyllite.
Mica Schist (Cambrian/Late Proterozoic)
Mica Schist - Garnet, staurolite, kyanite, or sillimanite occur locally; lenses and layers of quartz schist, micaceous quartzite, calc-silicate rock, biotite gneiss, amphibolite, and phyllite.
Migmatitic Biotite-Hornblende Gneisses (Middle Proterozoic)
Migmatitic Biotite-Hornblende Gneisses (1214 my) - unconformity; layered biotite-granite gneiss, biotite-hornblende gneiss, amphibolite, calc-silicate rock; locally contains relict granulite facies rock.
Phyllite and Schist (Cambrian/Late Proterozoic)
Phyllite and Schist - includes phyllonite and interlayered biotite gneiss.
Porphyroblastic Gneiss (Cambrian/Late Proterozoic)
Porphyroblastic Gneiss - massive to foliated, granodioritic, migmatitic.

New Hampshire

New Jersey

Biotite-Plagioclase Gneiss (Middle Proterozoic)
Biotite-Plagioclase Gneiss - White- to light-gray weathering, greenish-gray, medium-grained, moderately well layered gneiss composed of biotite, plagioclase and accessory amounts of hornblende, clinopyroxene, and, locally, garnet.
Biotite-quartz-oligoclase gneiss (Middle Proterozoic)
Biotite-quartz-oligoclase gneiss - White- to light-gray-weathering, light- to medium-gray or greenish-gray, fine- to coarse-grained, massive to moderately well layered, foliated gneiss composed of oligoclase or andesine, quartz, biotite, and, locally, garnet. Commonly interlayered with amphibolite.
Gneiss granofels and Migmatite (Middle Proterozoic)
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.
Hornblende-Plagioclase Gneiss (Middle Proterozoic)
Hornblende-Plagioclase Gneiss - White- to gray-weathering, greenish-gray, medium-grained, moderately well foliated gneiss containing hornblende, clinopyroxene, plagioclase and trace amounts of apatite, titanite and opaque minerals.
Hypersthene-Quartz-Oligoclase Gneiss (Middle Proterozoic)
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.
Manhattan Schist (Lower Cambrian and (or) Late Proterozoic)
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.
Monazite Gneiss (Middle Proterozoic)
Monazite Gneiss - Buff-weathering, light-greenish-gray to greenish-buff, fine- to medium-grained, moderately well-foliated, well-lineated gneiss composed of microcline microperthite, quartz, oligoclase, biotite, and monazite. Accessory minerals include hornblende, zircon and opaque minerals. Mapped in Fox Hill Range area
Quartz-Oligoclase Gneiss (Middle Proterozoic)
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.
Wissahickon Formation (Lower Cambrian and Late Proterozoic)
Wissahickon Formation - Fine- to medium-grained biotite-quartz-plagioclase schist and gneiss that contains thin amphibolite layers. Schist and gneiss in alternating layers suggest a turbidite sequence of shale and graywacke. The rocks are at high metamorphic grade, and, in places, the more pelitic parts have partly melted forming veins of migmatite. Some exposures show evidence of polymetamorphism as micaceous minerals occur both within the schistosity and as static porphyroblasts.

New Mexico

Nevada

New York

Bedford Gneiss (Ordovician?)
Bedford Gneiss - biotite-quartz-plagioclase gneiss and interlayered amphibolite; in part with augen of andesine and microcline.
Biotite-quartz-plagioclase gneiss (Middle Proterozoic)
Biotite-quartz-plagioclase gneiss - with subordinate biotite granitic gneiss, amphibolite, calcsilicate rock.
Biotite-quartz-plagioclase gneiss (Middle Proterozoic)
Biotite-quartz-plagioclase gneiss - commonly very low in biotite content, with interbedded feldspathic and biotitic quartzite and amphibolite; sillimanite and garnet common, graphite sporadic.
Biotite-quartz-plagioclase gneiss, amphibolite, and related migmatite (Middle Proterozoic)
Biotite-quartz-plagioclase gneiss, amphibolite, and related migmatite - locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.
Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic)
Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.
Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic)
Charnockite, granitic and quartz syenite gneiss - variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.
Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic)
Charnockite, mangerite, pyroxene-quartz syenite gneiss - overprint signifies inequigranular texture.
Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic)
Charnockite, mangerite, pyroxene-quartz syenite gneiss - overprint signifies inequigranular texture.
Cheshire Quartzite and Dalton Formation (Cambrian)
Cheshire Quartzite and Dalton Formation
Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock (Middle Proterozoic)
Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock - metasedimentary amphibolite, pyroxene granulite, and various gneisses; includes interlayered diopsidic and tremolitic marble and quartzite, and talc-tremolite rock (mined in Balmat-Edwards belt, northwest Adirondacks).
Fordham Gneiss (A member) (Precambrian - Middle Proterozoic )
Fordham Gneiss (A member) - fa: garnet-biotite-quartz-plagioclase gneiss, amphibolite, biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar granulite.
Fordham Gneiss (B member) (Precambrian - Middle Proterozoic )
Fordham Gneiss (B member) - fb: amphibolite, biotite and/or hornblende-garnet- quartz-plagioclase gneiss.
Fordham Gneiss (C and D member) (Precambrian - Middle Proterozoic )
Fordham Gneiss (C and D member) - fc: biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar lenses, amphibolite, biotite and/or hornblende-quartz-feldspar gneiss; fd: sillimanite-garnet schistose gneiss, quartzite.
Fordham Gneiss (E member) (Precambrian - Middle Proterozoic )
Fordham Gneiss (E member) - fe: garnet-biotite-quartz-plagioclase gneiss, and amphibolite.
Fordham Gneiss, undivided (Precambrian - Middle Proterozoic )
Fordham Gneiss, undivided - fe: garnet-biotite-quartz-plagioclase gneiss, and amphibolite; fd: sillimanite-garnet schistose gneiss, quartzite; fc: biotite- hornblende-quartz-plagioclase gneiss, quartz-feldspar lenses, amphibolite, biotite and/or hornblende-quartz-feldspar gneiss; fb: amphibolite, biotite and/or hornblende-garnet-quartz-plagioclase gneiss; fa: garnet-biotite-quartz-plagioclase gneiss, amphibolite, biotite-hornblende-quartz-plagioclase gneiss, quartz-feldspar granulite.
Garnet-bearing gneiss and interlayered quartzite (Middle Proterozoic)
Garnet-bearing gneiss and interlayered quartzite - contains varying amounts of biotite, garnet, sillimanite; minor marble, amphibolite, rusty paragneiss.
Garnet-biotite-quartz-feldspar gneiss (Middle Proterozoic)
Garnet-biotite-quartz-feldspar gneiss - quartzite, quartz-feldspar gneiss, calcsilicate rock.
Harrison/Ravenswood Gneiss (Ordovician?)
Harrison Gneiss - in New York and Connecticut, Brookfield diorite gneiss in Connecticut, and Ravenswood Gneiss in Brooklyn - biotite-hornblende-quartz- plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.
Hornblende-quartz syenite gneiss (Middle Proterozoic)
Hornblende-quartz syenite gneiss - overprint signifies inequigranular texture.
Hornblende syenite gneiss (Middle Proterozoic)
Hornblende syenite gneiss - overprint signifies inequigranular texture.
Hybrid rock: mangeritic to charnockitic gneiss (Middle Proterozoic)
Hybrid rock: mangeritic to charnockitic gneiss - with xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic)
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss.
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic)
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss.
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic)
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic)
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.
Manhattan Formation, undivided (Ordovician?)
Manhattan Formation, undivided - pelitic schists, amphibolite; Units ?Omb, ?Omc, and ?Omd may be Cambrian eugeosynclinal rocks thrust upon Oma; ?Omd - sillimanite-garnet-muscovite-biotite-plagioclase-quartz gneiss; ?Omc - sillimanite-garnet-muscovite-biotite-quartz-plagioclase schistose gneiss, sillimanite nodules, local quartz-rich layers; ?Omb - discontinous unit of amphibolite and ?Omc-type schist.
Poundridge Gneiss (Middle Proterozoic)
Poundridge Gneiss - biotite and/or hornblende-quartz-feldspar gneiss, similar to Yonkers Gneiss and parts of Fordham C member.
Quartz-plagioclase gneiss (Middle Proterozoic)
Quartz-plagioclase gneiss - may contain pyroxenes, hornblende, biotite; locally interlayered with amphibolite; subordinate biotite mesoperthite gneiss.
Rusty and gray biotite-quartz-feldspar gneiss (Middle Proterozoic)
Rusty and gray biotite-quartz-feldspar gneiss - rusty facies contains variable amounts of garnet, sillimanite, cordierite, graphite, sulfides; minor marble and calcsilicate rock.
Sillimanite-cordierite-almandine-biotite-quartz-feldspar gneiss (Middle Proterozoic)
Sillimanite-cordierite-almandine-biotite-quartz-feldspar gneiss.
Yonkers Gneiss (Middle Proterozoic)
Yonkers Gneiss - biotite and/or hornblende-quartz-feldspar gneiss.

Oregon

Pennsylvania

Rhode Island

South Carolina

South Dakota

Tennessee

Cranberry Granite (Precambrian)
Cranberry Granite - Complex of intertonguing rock types including migmatite, granitic gneisses, monzonite, quartz diorite, greenstone, mica and hornblende schists, abundant granitic pegmatite.
Mount Rogers Group including Bakersville Gabbro, Beech Granite, Cranberry Granite, and Roan Gneiss (Precambrian)
Mount Rogers Group - Metavolcanics, typically purplish and reddish; massive lavas and tuffs, altered rhyolites and quartz latites; strongly foliated; interbedded arkose, shale, and conglomerate. Thickness 1,000 to 3,000 feet; Includes Bakersville Gabbro - Metagabbro, dark, porphyritic; contains diorite, basalt, anorthosite, and diabase; occurs as thin to massive dikes and lenticular masses; Beech Granite - Granite, porphyritic, light-gray to reddish; coarse potash feldspar crystals and clustered interstitial mafics (chloritized biotite and hornblende) give spotted appearance; includes Max Patch Granite; Cranberry Granite - Complex of intertonguing rock types including migmatite, granitic gneisses, monzonite, quartz diorite, greenstone, mica and hornblende schists, abundant granitic pegmatite; and Roan Gneiss - Layered hornblende and garnet gneiss and granitic migmatite with zones of mica schist and amphibolite, foliation commonly contorted; contains numerous granitic and gabbroic dikes.
Roan Gneiss (Precambrian)
Roan Gneiss - Layered hornblende and garnet gneiss and granitic migmatite with zones of mica schist and amphibolite, foliation commonly contorted; contains numerous granitic and gabbroic dikes.

Texas

Virginia

Alligator Back Formation (Proterozoic Z-Cambrian)
Alligator Back Formation - Garnet-mica schist, garnet amphibolite, hornblende granite gneiss
Alligator Back Formation - Banded marble (Proterozoic Z-Cambrian)
Alligator Back Formation - Banded marble
Alligator Back Formation - Feldspathic metagraywacke (Proterozoic Z-Cambrian)
Alligator Back Formation - Meta-argillite is feldspathic metagraywacke; graphitic mica schist, and quartzite.
Amphibolite, Amphibole Gneiss, and Schist (Proterozoic Y)
Amphibolite, amphibole gneiss, and schist.
Amphibolite and Amphibole-Bearing Gneiss and Schist (Proterozoic)
Amphibolite and amphibole-bearing gneiss and schist.
Bassett Formation - Amphibolite. (Proterozoic Z-Cambrian)
Bassett Formation - Amphibolite.
Biotite Gneiss and Schist (Proterozoic)
Biotite gneiss and schist.
Border Gneiss (Proterozoic Y)
border gneiss - Gneiss.
Charnockite Gneiss (Proterozoic Y)
Charnockite gneiss
Diorite Gneiss (Proterozoic)
Diorite gneiss
Flint Hill Gneiss (Proterozoic Y)
Flint Hill Gneiss - Gneiss.
Fork Mountain Formation (Proterozoic Z-Cambrian)
Fork Mountain Formation - Quartzose mica schist, garnet-biotite gneiss, calc-silicate quartzite, and melange.
Gneiss (Proterozoic)
Gneiss as exotic blocks within melange units
Gneiss and Schist (Proterozoic)
Gneiss and schist.
Interlayered Mafic and Felsic Metavolcanic Rocks - Foliated felsite (Cambrian)
Interlayered Mafic and Felsic Metavolcanic Rocks - Foliated felsite
Interlayered Mafic and Felsic Metavolcanic Rocks - Quartz-muscovite schist and gneiss. (Cambrian)
Interlayered Mafic and Felsic Metavolcanic Rocks - Quartz-muscovite schist and gneiss.
Layered Biotite Granulite and Gneiss (Proterozoic Y)
Layered biotite granulite and gneiss.
Leucocratic Granulite and Gneiss (Proterozoic Y)
Leucocratic granulite and gneiss.
Mather Gorge Formation -- Schist (Proterozoic Z-Cambrian)
Mather Gorge Formation - Schist.
Metavolcanic and Metasedimentary Rocks - Felsic metatuff, mica schist, and gneiss. (Cambrian)
Metavolcanic and Metasedimentary Rocks - Felsic metatuff, mica schist, and gneiss.
Metavolcanic and Metasedimentary Rocks - Greenstone or amphibole gneiss. (Cambrian)
Metavolcanic and Metasedimentary Rocks - Greenstone or amphibole gneiss.
Muscovite Schist and Gneiss (Proterozoic Y)
Muscovite schist and gneiss
Mylonite, Mylonite Gneiss, and Cataclastic Rocks (Proterozoic - Paleozoic ?)
Mylonite, mylonite gneiss, and cataclastic rocks.
Shelton Formation (Ordovician)
Shelton Formation - Granite and quartz monzonite gneiss
State Farm Gneiss (Proterozoic Y)
State Farm Gneiss - Hornblende-biotite granite gneiss
Ta River Metamorphic Suite (Cambrian)
Ta River Metamorphic Suite - Amphibolite gneiss

Vermont

Cavendish Formation, Bull Hill Gneiss (Cambrian?)
Cavendish Formation, Bull Hill Gneiss - Quartz-plagioclase-microcline-biotite gneiss characterized in many areas by augen of microcline as much as 2 inches long; fine- to medium-grained quartz-plagioclase-biotite or biotite-muscovite gneiss. Cardinal Brook Intrusive Suite is here named in the cores of the Chester-Athens dome and Rayponda-Sadawga dome in the eastern and southern Green Mountains, VT, and the northern part of the Berkshire massif, MA. Includes the Stamford Granite of Hitchcock (1861), the Somerset Reservoir Granite (new name), the Harriman Reservoir Granite (new name), and the Bull Hill Gneiss of Richardson (1929-30). Because of uncertainty regarding the geologic position of the Bull Hill, it is restricted to the Chester and Athens domes and the original definition of Richardson is retained. Rocks mapped as Bull Hill in the Jamaica area are assigned to the Somerset Reservoir Granite and those in the Rayponda-Sadawga dome are assigned to the Harriman Reservoir Granite. Structural position is unclear. U-Pb zircon age is Middle Proterozoic (960-950 Ma). . [GNU Staff note--This report mistakenly uses the phrasing "Bull Hill Gneiss of Richardson (1929-30)" which would normally imply that the unit has not been adopted for use by the U.S. Geological Survey (USGS) because of inadequate definition by Richardson or successive workers in the area. However, in this report, the phrasing simply means that Richardson's definition and use are preferred over the usage on the VT State Geologic Map of Doll and others (1961) and that the unit meets the requirements for formal usage by the USGS.] (Ratcliffe, 1991).
gneiss, quartzite, calc-silicate granulite (Precambrian)
Gneiss, quartzite, calc-silicate granulite.
Hazens Notch Formation (Cambrian)
Hazens Notch Formation - Interbedded carbonaceous and noncarbonaceous quartz-sericite-albite-chlorite schist; grades to quartzite and gneiss. (Northern and Central Vermont). According to author, the name Hazens Notch is a big problem in VT stratigraphic nomenclature. In northern VT, it consists of carbonaceous and non-carbonaceous schist associated with ultramafics, mafic schists, and blueschists, while in the Camels Hump quad, it is considered to be strictly a carbonaceous albitic schist with associated mafic schist. The use of the name Hazens Notch is not recommended for the white albitic schist of the Fayston-Buels Gore area. Those rocks are here assigned to the newly named Fayston Formation (Walsh, 1992).
Missisquoi Formation, Whetstone Hill Member (Ordovician)
Missisquoi Formation, Whetstone Hill Member - Carbonaceous black to light gray phyllite and schist containing porphyroblasts of biotite and garnet; beds of gray micaceous quartzite, fine-grained biotite gneiss and amphibolite.
Mount Holly Complex (Precambrian)
Mount Holly Complex - Mainly fine- to medium-grained biotitic gneiss, locally muscovitic, and in western areas chloritic; massive and granitoid in some localities, fine-grained or schistose and compositionally layered in others; also abundant amphibolite and hornblende gneiss, and minor beds of mica schist, quartzite, and calc-silicate granulite; includes numerous small bodies of pegmatite and gneissoid granitic rock. Includes a suite of metatonalites, metatrondhjemite, and possible metadacite with chemical characteristics of a calc-alkaline volcanic-plutonic suite. Mappable units are College Hill Granite Gneiss and 10 unnamed subdivisions including several varieties of gneiss as well as schist, amphibolite, and quartzite. U-Pb zircon upper intercept ages of 1.35 to 1.30 Ga have been determined and interpreted as age of crystallization (Ratcliffe and others, unpub. data). Cores of abraded zircon obtained from College Hill Granite Gneiss of Mount Holly Complex have a U-Pb upper intercept age of 1245 +/-14 Ma, interpreted as crystallization age for that granite (Aleinikoff and others, 1990). Dust collected by abrasion of zircons, thought to represent migmatitic overgrowth, has a Pb-Pb age of approx 1100 Ma. These data suggest that College Hill Granite Gneiss was intruded at 1245 Ma and migmatized at 1100 Ma. On north and south slopes of College Hill, College Hill Granite Gneiss grades outward into migmatitic biotite granite gneiss of Mount Holly Complex. College Hill is discordant to contacts and folds in paragneiss units of Mount Holly Complex. Dacitic metavolcanics are found within Washington Gneiss of Berkshire massif of MA (Ratcliffe and Zartman, 1968). They are interbedded with thick succession of rusty-weathering, quartz-pebble gneisses, calc-silicate rocks and garnet-sillimanite schist similar to, but much thicker than, the rusty-weathering gneiss and schist unit of Mount Holly Complex exposed in Green Mountains of VT. It is possible that the metadacitic and metatrondhjemitic suite of VT constitutes a lateral, south-to-north facies of the Washington Gneiss of MA (Ratcliffe, in press).
Mount Holly Complex, quartzite and schist (Precambrian)
Mount Holly Complex, quartzite and schist - Quartzite, locally in massive beds as much as 30 ft thick, micaceous quartzite, and quartz-mica schist that commonly contains garnet or pseudomorphs (largely chlorite) after garnet; schists are locally rusty weathered and contain conspicuous flakes of graphite; also includes amphibolite and minor hornblende gneiss, biotite gneiss, and pegmatite.
Orfordville Formation, Post Pond Volcanics (Ordovician)
Orfordville Formation, Post Pond Volcanics - Greenstone, green chloritic schist interbedded with schistose felsite, quartz-feldspar-sericite schist; fine-grained chloritic, biotitic gneiss, all west of Ammonoosuc fault; mainly amphibolite east of the Ammonoosuc fault.

Washington

Mesozoic granitic rocks, undivided (Mostly Cretaceous-Jurassic)
Granite, quartz monzonite, quartz diorite, granodiorite, and trondhjemite. Includes diorite in southeastern Washington; diorite and gabbro near Concunully in Okanogan County; gneiss, schist, and migmatites in areas of Chelan, Colville, and Okanogan batholiths. Includes high-grade metamorphic rocks of Precambrian age in Spokane area.
Precambrian rocks, undivided (Proterozoic)
Predominantly phyllite with some schist, limestone, dolomite, quartzite, and volcanic rocks; northeastern Pend Oreille County. Mainly quartzite sandstone in upper part, dark-gray argillite with sandstone and limestone in middle part, and sandstone with argillite in lower part; southeastern Pend Oreille County. Banded slate with quartzite and dolomite; southwestern Stevens County. Quartzite, siliceous argillite, and argilliceous quartzite grading into argillite and quartz-mica schists form south ot north; southeastern Stevens County. Quartzite, argillite, quartz-feldspar gneiss, and other metamorphic rocks in northeastern Whitman and southeastern Spokane Counties are partly if not all extenstions of the Belt strata.
Precambrian volcanic rocks (Late-Proterozoic)
Mostly homogenous schistose greenstone; in places massive, mottled, and containing conspicuous calcite and epidote. Tuffaceous chlorite schist in upper part in northern Pend Oreille County. Amphibolite and plagioclase amphibolite in Little Pend Oreille Lakes district. Massive to sheared or schistose greenstone with dark-green ovoid spots; agglomeratic and amygodaloidal in places; sheared pillows near Blue Creek, central Stevens County; minor intrusive phase and probable center of eruption west of Finch magnesite quarry; central to southwestern Stevens County.
Pre-Carboniferous crystalline complex (Devonian)
Metahornblendite, amphibolite, gneiss, metadiorite, meta-quartz diorite, and trondhjemite. As klippes along western slope of northern Cascade Mountains.
Pre-Carboniferous intrusive rocks (Paleozoic)
Meta-quartz diorite, hypersthene diorite, and gneissose and directionless quartz diorite of eastern Skagit County. Quartz diorite and diorite in the San Juan Islands. Includes amphibolite and gneiss locally.
Pre-Tertiary basic intrusive rocks (Triassic-Permian)
Predominantly gabbro and metagabbro; includes hornblendite, peridotite, and pyroxenite. In Nighthawk district and near 49th Parallel in Okanogan County and in Orient district of Stevens County.
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 medium and high-grade zone (Early Jurassic-Triassic)
Schist, amphibolite, and minor lime-silicate rocks, marble, quartzite, and metaconglomerate.
Tertiary-Cretaceous basic intrusive rocks (Cretaceous-Jurassic)
Diorite and gabbro in western Snohomish County.
Tertiary-Cretaceous granitic intrusive rocks (Early Tertiary-Late Cretaceous)
Granite, granodiorite, trondhjemite, and quartz diorite. Late Cretaceous and/or early Tertiary.
Upper Paleozoic rocks, undivided (Ordovician)
Mostly graywacke, interbedded quartzite and phyllite, greenstone and serpentine, and black shale with minor limestone. Some quartz-mica schist in Bald Knob area of Ferry County. Schist, gneiss, and amphibolite in other parts of Ferry County. Some rocks of lower Paleozoic age, possibly Precambrian, and Mesozoic may be included.

Wisconsin

Gneiss and amphibolite (Early Proterozoic)
Gneiss and amphibolite - Interlayered quartzofeldpathic gneiss and amphibolite between Athens shear zone and Owen fault, central Wisconsin
Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) (Late Archean)
Gneiss and amphibolite (Late Archean, 2.640-2.750 Ma) - Interlayered quartzofeldspathic gneiss and amphibolite in Marenisco, Mich., area and northwestern Wisconsin. Protoliths are bimodal intermediate and mafic volcanic rocks (Sims and others, 1984).
Gneiss, migmatite, and amphibolite (about 2800 Ma) (Late Archean)
Gneiss, migmatite, and amphibolite (about 2800 Ma) - Quartzofeldspathic gneiss and less abundant amphibolite and migmatite. Includes granitoid rocks. Granitic gneiss at Port Edwards, WI on Wisconsin River has a U-Pb zircon age of 2870 +/- 13 Ma, and gneiss at Jim Falls in Chippewa River valley has a U-Pb zircon age of 2522 +/- 22 Ma (Sims and others, 1989)
Granite-tonalite (Early Proterozoic)
Granite-tonalite - Gray to pinkish-gray, medium-grained, generally equigranular granite to tonalite and granitoid gneiss; locally includes diorite. Intrudes older metavolcanic rocks. Zircon ages range from 1852 +/- 15 to 1862 +/- 5 Ma
Migmatitic gneiss and amphibolite (Late to Early Archean) (Archean)
Migmatitic gneiss and amphibolite (Late to Early Archean) - Varied gneisses of mostly unknown age in cores of gneiss domes and fault-bounded uplifts (Archean gneiss terranes). Except for the Watersmeet dome (Late to Early Archean), all dated rocks are Late Archean. Includes granite of Late Archean age that transgresses gneisses and amphibolite.
Tuff breccia schist and minor iron-formation (Late Archean)
Tuff breccia schist and minor iron-formation - Pink and gray, layered quartzofeldspathic schist of intermediate volcanic composition and associated thin iron-formation. Felsic gneiss at Arbutus Dam on Black River at Hatfield has U-Pb zircon age of about 2800 Ma (Sims and others, 1989)

West Virginia