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Geologic units containing amphibolite

Amphibolite

A crystalloblastic rock consisting mainly of amphibole and plagioclase with little or no quartz.

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Alabama

Beaverdam Amphibolite (Precambrian to Paleozoic): Beaverdam Amphibolite - dark-green to dark-gray hornblende amphibolite, extensively sheared and folded, and locally retrograded to actinolite-tremolite-chlorite schist. Includes all amphibolite associated with the Wedowee Group.
Dadeville Complex; Agricola Schist (Precambrian to Paleozoic): Agricola Schist - biotiite +/- garnet +/- sillimanite-feldspar-quartz schist, interlayered with thin-bedded dark-brown hornblende amphibolite; contains pegmatite pods and veins.
Dadeville Complex; Camp Hill Granite Gneiss (Precambrian to Paleozoic): Camp Hill Granite Gneiss - coarse to medium-grained foliated granite to quartz diorite (tonalite) gneiss, locally biotite-rich; locally contains thin amphibolite pods and lenses. Boundary between Rock Mills Granite Gneiss and Camp Hill Granite Gneiss arbitrarily defined.
Dadeville Complex; Mafic and ultramafic rock (Precambrian to Paleozoic): Mafic and ultramafic rock - ultramafic rock including enstatite pyroxenite, layered actinolite-tremolite amphibolite altered locally to serpentine, anthophyllite, and talc; metanorite; metagabbro; hornblendite; garnet-hornblendite, and massive amphibolite.
Dadeville Complex; Rock Mills Granite Gneiss (Precambrian to Paleozoic): Rock Mills Granite Gneiss - coarse to medium-grained biotite granite gneiss; locally includes thick bands of epidote and thin, small amphibolite bodies. Boundary between Rock Mills Granite Gneiss and Camp Hill Granite Gneiss arbitrarily defined.
Dadeville Complex; Ropes Creek Amphibolite (Precambrian to Paleozoic): Ropes Creek Amphibolite - layered and massive amphibolite; locally includes hornblende migmatite and ultramafic pods.
Dadeville Complex; Waresville Schist (Precambrian to Paleozoic): Waresville Schist - banded amphibolite interlayered with chlorite schist, chlorite amphibolite, chlorite-actinolite schist, chlorite +/- magnetite quartzite, and actinolite quartzite; may include small ultramafic pods.
Dadeville Complex; Waverly Gneiss (Precambrian to Paleozoic): Waverly Gneiss - feldspathic biotite-hornblende gneiss with thin layers of amphibolite, calc-silicate rock, garnet quartzite, and muscovite schist; locally rich in manganese.
Emuckfaw Group; Emuckfaw Group undifferentiated in part (Precambrian to Paleozoic): Emuckfaw Group undifferentiated in part - interbedded muscovite +/- garnet-biotite schist, metagraywacke, calc-silicate rock, and quartzite; rare thin amphibolite. Includes thin layers of aluminous graphitic schist. Locally sheared to mylonite schist.
Hatchet Creek Group; Hanover Schist (Precambrian to Paleozoic): Hanover Schist - coarse to fine-grained feldspathic biotite-sericite-quartz-muscovite schist, commonly containing staurolite, garnet, and locally sillimanite in northeastern outcrop areas includes zones of aluminous graphite schist, hornblende quartzite, garnet quartzite, and rare amphibolite. Schist commonly retrograded to sericite-garnet-quartz schist. Numerous granitic pegmatites.
Ketchepedrakee Amphibolite (Precambrian to Paleozoic): Ketchepedrakee Amphibolite - dark-green to black fine to coarse-grained, layered to massive amphibolite mixed with zones of chlorite actinolite schist, includes all amphibolite associated with the Poe Bridge Mountain Group.
Mitchell Dam Amphibolite (Precambrian to Paleozoic): Mitchell Dam Amphibolite - dark-green to black fine to coarse-grained, thin-layered to massive hornblende-actinolite amphibolite; includes all amphibolite associated with the Higgins Ferry and Hatchet Creek Groups.
Motts Gneiss, Unnamed unit (Precambrian to Paleozoic): Motts Gneiss, Unnamed unit - unnamed unit comprised of masses of epidote-hornblende-oligoclase mylonitic gneiss and amphibolite.
Uchee Complex; Phenix City Gneiss (Precambrian to Paleozoic): Phenix City Gneiss - biotite-epidote quartz diorite gneiss and biotite-hornblende gneiss; locally includes migmatitic amphibolite; cut by numerous granitic veins.

Arizona

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)
Orocopia Schist (Late Cretaceous to Early Tertiary): Mostly gray, fine-grained quartz-feldspar-mica schist, with sparse metabasalt and metachert. The unit is exposed in tectonic windows in the southwestern corner of Arizona. It is interpreted as metamorphosed marine sandstone that was tectonically emplaced beneath southwestern Arizona during early Tertiary subduction of Pacific Ocean sea floor. (65-165 Ma)

California

Franciscan Complex, unit 1 (Coast Ranges) (Jurassic to Cretaceous): Franciscan complex: Cretaceous and Jurassic sandstone with smaller amounts of shale, chert, limestone, and conglomerate. Includes Franciscan melange, except where separated--see KJfm.
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 volcanic rocks, unit 4 (Peninsular Ranges) (Late Jurassic to Early Cretaceous): Undivided Mesozoic volcanic and metavolcanic rocks. Andesite and rhyolite flow rocks, greenstone, volcanic breccia and other pyroclastic rocks; in part strongly metamorphosed. Includes volcanic rocks of Franciscan Complex: basaltic pillow lava, diabase, greenstone, and minor pyroclastic rocks
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
Paleozoic marine rocks, undivided, unit 9 (Western Klamath Mountains) (Devonian to Jurassic): Undivided Paleozoic metasedimentary rocks. Includes slate, sandstone, shale, chert, conglomerate, limestone, dolomite, marble, phyllite, schist, hornfels, and quartzite
Paleozoic metavolcanic rocks, unit 3 (Northwestern Sierra Nevada) (Permian to Jurassic): Undivided Paleozoic metavolcanic rocks. Mostly flows, breccia and tuff, including greenstone, diabase, and pillow lavas; minor interbedded sedimentary rocks
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 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
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 2 (Southern and West-central California) (Late Cretaceous to Eocene): Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.
Schist of various types and ages, unit 7 (Klamath Mountains) (Devonian): 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.
Undivided pre-Cenozoic metavolcanic rocks, unit 2 (undivided) (Paleozoic(?) to Mesozoic(?)): Undivided pre-Cenozoic metavolcanic rocks. Includes latite, dacite, tuff, and greenstone; commonly schistose.

Colorado

Red Creek Quartzite (Archean): Metaquartzite, amphibolite, and mica schist. Present only in small area at Utah border in Uinta Mountains

Connecticut

Allingtown Metavolcanics plus Maltby Lakes Metavolcanics (Middle? Ordovician): Allingtown Metavolcanics plus Maltby Lakes Metavolcanics - Allingtown Metavolcanics - Green, fine-grained, massive greenstone, composed of epidote, actinolite, albite, and chlorite, commonly with abundant megacrysts of saussurite, interlayered with minor green phyllite, generally containing quartz and sericite. Dark amphibole in western outcrops. Maltby Lakes Metavolcanics - Green to gray-green, fine-grained, massive to well-foliated and layered greenstone, greenschist, and schist; also dark amphibolite to west and southwest.
Amphibolite-bearing unit of Manhattan Schist (Cambrian?): Amphibolite-bearing unit of Manhattan Schist - Like Manhattan Schist but with numerous lenses and layers of amphibolite.
Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician): Amphibolite unit [in Ratlum Mountain Schist] - 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.
Basal member [of The Straits Schist] (Silurian): Basal member [of The Straits Schist] ( = Russell Mountain Formation of Massachusetts) - Distinguished by presence of layers of amphibolite, marble, calc-silicate rock, and quartzite within more uniform schist like that on either side. Minor, unevenly distributed mineralization in W, Bi, Cu, Ni, and other metals.
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).
Brookfield Gneiss (Middle? Ordovician): Brookfield (dioritic and granodioritic) Gneiss (including Newtown Gneiss of Crowley, 1968) - Dark and light, commonly speckled or banded, medium- to coarse-grained, massive to poorly foliated gneiss, composed of plagioclase, biotite, and hornblende, generally with quartz and K-feldspar, the latter commonly as megacrysts 1 to 3 cm across (also plagioclase megacrysts in darker rocks), locally associated with amphibolite or hornblende schist.
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.
Cobble Mountain Formation (Middle Ordovician): Cobble Mountain Formation - Gray to silver (not rusty), medium- to coarse-grained, generally layered schist and granofels, composed of quartz, oligoclase, muscovite, biotite, and garnet, and locally kyanite and staurolite or sillimanite. Some amphibolite layers.
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.
Glastonbury Gneiss (Middle? Ordovician): Glastonbury Gneiss - Gray, medium- to coarse-grained, massive to well-foliated granitoid gneiss composed of oligoclase, quartz, microcline, and biotite (as patches), also epidote and hornblende in many areas, commonly associated with layers of amphibolite; elsewhere minor muscovite and garnet.
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.
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.
Hornblende gneiss member [of Collinsville Formation] (Middle Ordovician): Hornblende gneiss member [of Collinsville Formation] - Dark, fine- to medium-grained, well-layered amphibolite and hornblende gneiss, composed of hornblende and plagioclase, commonly with biotite, garnet, or epidote, interlayered with light-gray felsic gneiss and pink quartz-spessartine rock (coticule). Grades into Bristol Gneiss.
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.
Lower member [of Middletown Formation] (Middle Ordovician): Lower member [of Middletown Formation] - Dark- to medium-gray amphibolite and hornblende gneiss, commonly with garnet, diopside, or epidote, interlayered with light-gray gneiss composed of oligoclase, quartz, biotite, and generally one or more amphiboles, also garnet.
Lower slice of Canaan Mountain Schist (Cambrian?): Lower slice of Canaan Mountain Schist - Dark-gray, rusty-weathering, coarse-grained, well-foliated and moderately well layered schist composed of quartz, plagioclase, biotite, muscovite, and generally garnet and sillimanite (or minor staurolite). Amphibolite layers rather rare.
Maltby Lakes Metavolcanics (Middle? Ordovician): Maltby Lakes Metavolcanics - Green to gray-green, fine-grained, massive to well-foliated and layered greenstone, greenschist, and schist; also dark amphibolite to west and southwest.
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).
Massive mafic rock (in Middletown Formation) (Middle Ordovician): Massive mafic rock (in Middletown Formation) - Dark, coarse-grained, massive amphibolite and metagabbro, composed of hornblende and plagioclase; in places with quartz and epidote, in others with patches of actinolite or anthophyllite, chlorite, and epidote or garnet. May be intrusive.
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.
New London Gneiss (Proterozoic Z?): New London Gneiss - New London consists of a layered facies and a massive facies. Layered facies described as alternating layers of light-colored biotite-quartz-plagioclase gneiss and amphibolite. Massive facies described as a granodiorite gneiss with a uniform texture, grain size, and color. Contains shiny black biotite plates and distinctive magnetite grains. New London consists of a layered facies and a massive facies. Layered facies described as alternating layers of light-colored biotite-quartz-plagioclase gneiss and amphibolite. Massive facies described as a granodiorite gneiss with a uniform texture, grain size, and color. Contains shiny black biotite plates and distinctive magnetite grains (Skehan and Rast, 1990).
Oronoque Schist (Lower? Ordovician): Oronoque Schist - Gray to silver, medium- to fine-grained, well-layered to laminated schist and granofels, composed of quartz, oligoclase, or albite, muscovite or sericite, biotite, or chlorite, and in western belt local garnet, staurolite, and kyanite. Small lenses of amphibolite or greenstone.
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.
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.
Ratlum Mountain Schist (Lower? Ordovician): 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.
Ratlum Mountain Schist (Lower Ordovician): 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.
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).
Rowe Schist (Lower Ordovician or Cambrian or both): Rowe Schist - Light-gray to silvery, fine- to medium-grained, generally poorly layered schist, composed of quartz, muscovite, biotite, oligoclase, and generally garnet, staurolite, and kyanite or sillimanite. Layers of granofels common; also some layers of amphibolite, quartz-spessartine rock (coticule), and calc-silicate rock.
Rowe Schist plus Amphibolite unit [in Rowe Schist] (Lower Ordovician or Cambrian or both): Rowe Schist plus Amphibolite unit [in Rowe Schist] - Rowe Schist - Light-gray to silvery, fine- to medium-grained, generally poorly layered schist, composed of quartz, muscovite, biotite, oligoclase, and generally garnet, staurolite, and kyanite or sillimanite. Layers of granofels common; also some layers of amphibolite, quartz-spessartine rock (coticule), and calc-silicate rock. Amphibolite unit [in Rowe Schist] - Black or mottled, generally massive amphibolite and hornblende gneiss, composed of hornblende and andesine.
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.
Southbridge Formation (Silurian or Ordovician or both): Southbridge Formation - Dark- to light-gray, locally rusty, fine- to medium-grained interlayered granofels and schist, composed of quartz, plagioclase, and biotite, with muscovite in schist, and amphibole, calc-silicate minerals, K-feldspar in certain layers; also locally mappable units and thinner layers of calc-silicate rock, amphibolite, and sillimanite-garnet and sillimanite-graphite-pyrrhotite schist.
Sweetheart Mountain Member [of Collinsville Formation] (Middle Ordovician): Sweetheart Mountain Member [of Collinsville Formation] - Gray and silvery (not rusty), medium- to coarse-grained, poorly layered schist, composed of quartz, oligoclase, biotite, muscovite, and garnet, and in places kyanite or sillimanite. Amphibolite layers common; also layers of quartz-spessartine rock (coticule). In the Bristol quad., CT, Collinsville Formation is revised to include a basal unnamed hornblende gneiss member (was upper part of Stanley's (1964) Bristol Member), a middle unnamed metaquartzite member, and the upper Sweetheart Mountain Member. Bristol Member of Stanley (1964) is raised in rank to Bristol Gneiss in the report area. Collinsville unconformably underlies The Straits Schist. Inferred age is Middle Ordovician (Simpson, 1990).
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.
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

Amphibolite (Paleozoic): Amphibolite - amphibolite

Georgia

Amphibolite (Precambrian-Paleozoic): Amphibolite
Amphibolite/ Biotitic Gneiss/ Quartz Sericite Schist (Precambrian-Paleozoic): Amphibolite/ Biotitic Gneiss/ Quartz Sericite Schist
Amphibolite/ Epidote Quartzite/ Granite Gneiss (Precambrian-Paleozoic): Amphibolite/ Epidote Quartzite/ Granite Gneiss
Amphibolite / gabbro (Precambrian-Paleozoic): Amphibolite / gabbro
Amphibolite/ Metagraywacke/ Mica Schist (Precambrian-Paleozoic): Amphibolite/ Metagraywacke/ Mica Schist
Amphibolite/ Mica Schist/ Biotitic Gneiss (Precambrian-Paleozoic): Amphibolite/ Mica Schist/ Biotitic Gneiss
Amphibolite/ Ultramafic (Precambrian-Paleozoic): Amphibolite/ Ultramafic
Amphibolitic Schist/ Amphibolite (Precambrian-Paleozoic): Amphibolitic Schist/ Amphibolite
Amphibolitic Schist/ Amphibolite-Metagraywacke/ Mica Schist (Precambrian-Paleozoic): Amphibolitic Schist/ Amphibolite-Metagraywacke/ Mica Schist
Biotite Gneiss/ Amphibolite (Age not given): Biotite Gneiss/ Amphibolite
Biotite Granite Gneiss/ Feldspathic Biotite Gneiss/ Amphibolite Hornblende Gneiss (Precambrian-Paleozoic): Biotite Granite Gneiss/ Feldspathic Biotite Gneiss/ Amphibolite Hornblende Gneiss
Biotitic Gneiss / Amphibolite (Precambrian-Paleozoic): Biotitic Gneiss / Amphibolite
Biotitic Gneiss / Mica Schist/ Amphibolite (Precambrian-Paleozoic): Biotitic Gneiss / Mica Schist/ Amphibolite
Epidote Quartzite/ Amphibolite/ Sericite Schist/ Biotite Granite Gneiss (Precambrian-Paleozoic): Epidote Quartzite/ Amphibolite/ Sericite Schist/ Biotite Granite Gneiss
Garnet Mica Schist/ Amphibolite (Precambrian-Paleozoic): Garnet Mica Schist/ Amphibolite
Granite/ biotite granite/ amphibolite (Precambrian-Paleozoic): Granite/ biotite granite/ amphibolite
Granite Gneiss/ Amphibolite (Precambrian-Paleozoic): Granite Gneiss/ Amphibolite
Hornblende-Biotite Gneiss/ Amphibolite (Precambrian-Paleozoic): Hornblende-Biotite Gneiss/ Amphibolite
Hornblende Gneiss/ Amphibolite (Precambrian-Paleozoic): Hornblende Gneiss/ Amphibolite
Hornblende Gneiss/ Amphibolite/ Granite Gneiss (Precambrian-Paleozoic): Hornblende Gneiss/ Amphibolite/ Granite Gneiss
Metagraywacke/ Mica Schist-Quartzite/ Amphibolite (Precambrian-Paleozoic): Metagraywacke/ Mica Schist-Quartzite/ Amphibolite
Mica Schist/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Amphibolite
Mica Schist/ Gneiss/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Gneiss/ Amphibolite
Mica Schist/ Quartzite/ Gneiss/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Quartzite/ Gneiss/ Amphibolite
Quartzite/ Mica Schist/ Amphibolite (Precambrian-Paleozoic): Quartzite/ Mica Schist/ Amphibolite
Sericite Schist/ Amphibolite (Precambrian-Paleozoic): Sericite Schist/ Amphibolite
Sericite Schist/ Amphibolite/ Granite gneiss (Precambrian-Paleozoic): Sericite Schist/ Amphibolite/ Granite gneiss
Sillimanite Schist/ Amphibolite (Precambrian-Paleozoic): Sillimanite Schist/ Amphibolite
Sillimanite Schist/ Gneiss/ Amphibolite (Precambrian-Paleozoic): Sillimanite Schist/ Gneiss/ Amphibolite

Idaho

Amphibolite after gabbro, diabase, and diorite; Middle Proterozoic sill-like intrusions; southern and northern Belt provinces (Middle Proterozoic): Younger or Intermediate Precambrian age intrusive rock undifferentiated; Intrusive rock of eastern Idaho; appears older than Cretaceous, possibly Precambrian; Highly metamorphosed rock of central Idaho; age and origin of rock questionable.
Biotite schist, hornfels, amphibolite, and mylonite; Middle Proterozoic rocks of the Prichard Formation, metamorphosed near the Cretaceous Kaniksu batholith; northern Belt province (Eocene to Middle Proterozoic): Intermediate Precambrian age metasediments; generally low-to-medium grade; argillite, siltite and minor quartzite of northern Idaho.
Felsic augen gneiss after porphyritic granite; Middle Proterozoic; southern Belt province (Middle Proterozoic): Augen gneiss, amphibolite and other metamorphosed igneous rocks; possibly Precambrian.
Gabbro, diorite, amphibolite, lamprophyre; Tertiary to Late Proterozoic, undivided; northern Idaho (Tertiary to Late Proterozoic): Younger Precambrian dioritic and amphibolitic sills of northern Idaho.
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
Limestone, slate; Upper Triassic greenschist-facies metamorphic rocks; western Idaho, Blue Mountains island-arc complex; (Late Triassic): Upper Triassic shale overlying reefal limestone and dolomite in west-central Idaho.
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.
Mica schist, marble, quartzite, and amphibolite; Early Middle to Early Proterozoic metasedimentary rocks; southern Belt province (Early Middle Proterozoic to Early Proterozoic): Older Precambrian high-grade metamorphic complex of eastern Idaho.
Mica schist, quartzite, migmatite, amphibolite; Middle to Early Proterozoic metamorphic rocks; northern Belt province, Spokane dome of Priest River metamorphic core complex (Middle Proterozoic to Early Proterozoic): Precambrian, high-grade metamorphic rock; metasediment; kyanite-silimanite garnet-mica coarse-grained schist and gneiss; minor quartzite
Orthogneiss, mica schist, and amphibolite; Early Proterozoic to Late Archean metamorphic rocks; south-central Idaho; Albion Range metamorphic core complex (Early Proterozoic to Late Archean): Precambrian, high-grade metamorphic rock; metasediment subdivisions are (PC3, PC2, PC1).
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

Massachusetts

Ammonoosuc Volcanics (Middle Ordovician): Ammonoosuc Volcanics - Amphibolite, felsic gneiss, garnet-amphibole quartzite, and marble too thin to show separately at map scale. Gedrite, anthophyllite, cummingtonite locally abundant in amphibolite layers.
Belchertown Complex (age uncertain): Belchertown Complex (intrudes De) - Inclusions of amphibolite (age uncertain).
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.
Blackstone Group (Proterozoic Z): Blackstone Group - Greenstone and amphibolite - Includes Hunting Hill Greenstone.
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.
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 - Red rusty-weathering schist containing thin beds of white quartz-plagioclase granofels and vitreous quartzite. Local amphibolite and thin anthophyllite amphibolite.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Amphibolite, locally very garnetiferous, containing beds of felsic 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 - Interlayered amphibolite and white felsic gneiss containing biotite, hornblende, and magnetite. Local calc-silicate beds. Coticule-bearing granofels, muscovite quartzite and amphibolite in upper part.
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 - Brown to rusty-brown schist containing coticule and locally massive amphibolite at base.
Collinsville Formation (Middle Ordovician or older): Collinsville Formation - Felsic gneiss containing scattered biotite, magnetite, garnet and hornblende. Local beds of amphibolite.
Diorite (Proterozoic Z): Diorite - Medium-grained hornblende diorite metamorphosed in part to amphibolite and hornblende gneiss.
Erving Formation (Lower Devonian): Erving Formation - Biotite-plagioclase granofels, minor mica schist and calc-silicate granofels, and layers of epidote amphibolite.
Erving Formation (Lower Devonian): Erving Formation - Mixed mica schist and amphibolite where mapped separately.
Erving Formation (Lower Devonian): Erving Formation - Amphibolite where mapped separately.
Fourmile Gneiss (Ordovician, Cambrian, or Proterozoic Z): Fourmile Gneiss - Layered to massive biotite-feldspar gneiss and amphibolite.
Gabbro (Proterozoic Z): Gabbro - Hornblende gabbro and hornblende-pyroxene gabbro metamorphosed in part to hornblende gneiss and amphibolite.
Gile Mountain Formation (Lower Devonian): Gile Mountain Formation - Amphibolite, hornblende schist.
Gneiss and schist near New Bedford (Proterozoic Z): Gneiss and schist near New Bedford - Hornblende and biotite schist and gneiss, amphibolite.
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 - Interbedded amphibolite, greenstone, feldspathic schist and granofels. Coarse plagioclase in some amphibolite near top; local coarse hornblende blades or sprays. Sparse coticule (Emerson, 1917, p. 43). 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 - Medium-gray plagioclase-hornblende-chlorite schist containing megacrysts of plagioclase and angular fragments of feldspar granofels, epidote-plagioclase granofels, and dark-gray amphibolite. 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 - Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase 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 - Undifferentiated Hoosac Formation.
Hoosac Formation (Lower Cambrian and Proterozoic Z): Hoosac Formation - Amphibolite.
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.
Massive amphibolite of uncertain age (Proterozoic Y?): Massive amphibolite of uncertain age - Near South Sandisfield.
Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z): Monson Gneiss - Layered to massive biotite-plagioclase gneiss, amphibolite, microcline augen gneiss.
Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z): Monson Gneiss - Amphibolite where mapped separately.
Moretown Formation (Middle Ordovician or older): Moretown Formation - Green to dark-green greenstone or amphibolite.
Moretown Formation (Middle Ordovician or older): Moretown Formation - Nubble garnet schist, pinstriped granofels, and fine-grained amphibolite in equal parts.
Mount Mineral Formation (Proterozoic Z): Mount Mineral Formation (Probably correlates with Poplar Mountain Gneiss but is more aluminous) - Aluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.
Nashoba Formation (Ordovician or Proterozoic Z): Nashoba Formation - Boxford Member - Thin bedded to massive amphibolite, minor biotite gneiss. Of the 10 members of the Nashoba Formation defined by Bell and Alvord (1976), only amphibolitic Boxford Member, at the presumed base of Nashoba is separated out on MA State bedrock map of Zen and others (1983) because it is the only member clearly identified in several locations. 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 is made in this report.] (Goldsmith, 1991).
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).
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Biotite gneiss of volcanic derivation, minor amphibolite and sulfidic schist.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Sulfidic mica schist and abundant amphibolite.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Sulfidic mica schist and subordinate amphibolite.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Amphibolite where mapped separately.
Partridge Formation (Middle Ordovician): Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Felsic gneiss of volcanic derivation and minor amphibolite.
Paxton Formation (Silurian): Paxton Formation - Amphibolite. The Paxton, here of group rank, includes strata formerly mapped in CT as the Hebron Formation and in MA as the Paxton Formation. It conformably overlies the Oakdale Formation and structurally and conformably underlies the Brimfield Group. It is undivided in central MA; in northeast CT and adjacent MA it is divided into the Dudley and Southbridge Formations. Age is Late Proterozoic(?) based on the intrusion of 440 m.y. Hedgehog Hill gneiss into the overlying Brimfield Group and an age of 1188 m.y. for detrital zircons from the Paxton (Pease, 1989).
Plainfield Formation (Proterozoic Z): Plainfield Formation - Quartzite, pelitic schist, minor calc-silicate rock and amphibolite. Plainfield Formation extend into MA in Webster-Oxford area from eastern CT and western RI along west flank of Rhode Island batholith, along same strike as elongate lenses of Westboro Formation (as shown on State bedrock map of Zen and others, 1983). Lithology of Plainfield in New London area of southeastern CT (Goldsmith, 1966, 1976) and in eastern CT (Harwood and Goldsmith, 1971), and its structural and stratigraphic position indicate Plainfield and Westboro are equivalent. Plainfield is truncated along CT-RI border by Lake Char fault; however, in New London area, Plainfield is overlain by suite of largely mafic metavolcanic rocks (Waterford Group of Goldsmith, 1980), a relationship similar to that of the Westboro Formation and overlying metavolcanic rocks. Base of Plainfield is unknown, but gneiss and schist in center of Lyme dome may lie below it. Probably equivalent to quartzite and schist of Blackstone Group on basis of similar lithology and structural relations with Rhode Island batholith rocks (Goldsmith, 1991).
Quinebaug Formation (Ordovician, Cambrian, or Proterozoic Z): Quinebaug Gneiss - Amphibolite, biotite and hornblende gneiss, felsic gneiss, and calc-silicate gneiss.
Reubens Hill Formation (Silurian or Ordovician): Reubens Hill Formation - Amphibolite, hornblende-chlorite schist, and feldspathic schist. Includes metamorphosed diorite.
Rowe Schist (Lower Ordovician and Cambrian): Rowe Schist - Fine- to medium-grained, well-layered and foliated amphibolite; epidote-rich layers locally abundant. Includes its typical Chester Amphibolite Member at Chester, Massachusetts.
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 - Sulfidic sillimanite schist, sillimanite schist and gneiss, biotite gneiss; minor amphibolite, calc-silicate gneiss and marble.
Waits River Formation (Lower Devonian): Waits River Formation - Amphibolite or hornblende schist locally containing conspicuous hornblende or garnet megacrysts. Rocks mapped as Conway Schist by Emerson (1898, 1917) and subsequently subdivided by Segerstrom (1956) and Willard (1956) were mapped across the MA-VT State line as Waits River and Gile Mountain Formations by Doll and others (1961) on Centennial Geologic Map of Vermont. Although controversy still exists over relative ages, detailed reconnaissance mapping by authors and S.F. Clark, Jr., L.M. Hall, and J.W. Pferd shows that Waits River and Gile Mountain Formations are readily distinguished in the field. For these reasons, and to maintain continuity across the State line, authors chose to follow VT nomenclature on here and on MA State bedrock geologic map (Zen and others, 1983). Primary difference between Waits River and Gile Mountain is presence in Gile Mountain of beds of noncalcareous, commonly micaceous quartzite. Both formations contain conspicuous beds of punky brown-weathering impure marble or calcareous granulite, mostly in Waits River and less abundant in Gile Mountain. Predominant lithology of both formations is typically contorted gray, graphitic, locally very sulfidic, moderately aluminous mica schist containing quartz veins. Gradational but definitely significant boundary can be mapped between both formations. Amphibolite in both formations may correlate with Standing Pond Volcanics occurring at or near Waits River-Gile Mountain contact in VT. Report goes into great detail regarding informal subdivision of each formation. Rocks previously mapped as Waits River Formation northeast of Shelburne Falls dome by Hatch and Hartshorn (1968) are here reassigned to an unnamed member of Goshen Formation because the rocks are indistinguishable from the Goshen. Goshen-Waits River contact is defined as the line along which, going eastward, the schist changes from aluminous, planar-bedded, and virtually quartz-free (Goshen), to alumina-poor, contorted, and rich in quartz veins (Waits River) (Hatch and others, 1988).
Washington Gneiss (Proterozoic Y): Washington Gneiss - Coarse- to medium-grained hornblende-garnet amphibolite, hornblende-plagioclase gneiss and phlogopite-hornblende-plagioclase amphibolite (metabasalt).
Westboro Formation (Proterozoic Z): Westboro Formation - Quartzite, schist, calc-silicate quartzite, and amphibolite. Consists of quartzite and argillite in Saugus and Lynnfield areas. Westboro Formation consists primarily of orthoquartzite and subordinate mica schist, calc-silicate rock, amphibolite, and quartzitic biotite gneiss and schist. Westboro as portrayed by Nelson (1974), Bell and Alvord (1976), and Hepburn and DiNitto (1978) are correlative [with varying certainty]. West and south of Boston, disconnected masses of quartzite and associated rocks are shown on State bedrock map by Zen and others (1983) as Westboro although not continuous with belts mapped by Nelson (1974) or Hepburn and DiNitto (1978). Includes isolated quartzite masses mapped by Castle (1964) in Reading area. On State bedrock map, arbitrarily includes thin quartzite mapped as Burlington Formation by Bell and Alvord (1976) because the units are similar and to reduce number of small units on State map. Rocks mapped as Rice Gneiss by Nelson (1974) were included in unnamed metamorphosed mafic and felsic volcanic unit on State bedrock map, but author now feels it should be either a part of Westboro, or a separate unit below it. Westboro in Framingham area and to the northeast is overlain by unnamed assemblage of metamorphosed mafic and felsic volcanic rocks. South of town of Westborough, Westboro is truncated by Bloody Bluff-Lake Char fault system. Intruded by Proterozoic Z batholithic rocks. Equivalent to Plainfield Formation of eastern CT because it lies in same strike belt, and is probably equivalent to Quinnville Quartzite and unnamed mica schist and phyllite of Blackstone Group. Contact between Westboro and Blackstone is arbitrary on State bedrock map on basis of proximity of isolated exposures of the two units to their respective type areas. No area of continuous exposure exists between Westboro and Blackstone (Goldsmith, 1991).

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.
Georgetown Mafic Complex (Late Precambrian (?) - Early Paleozoic ): Georgetown Mafic Complex - Poorly exposed complex of tonalite, dark quartz diorite, gabbro, amphibolite, and undifferentiated basic rocks.
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.
Metagabbro and Amphibolite (Early Paleozoic (?)): Metagabbro and Amphibolite - Weakly to strongly lineated metagabbro and epidote amphibolite.
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

Cambrian Jim Pond Formation (Cambrian): Cambrian Jim Pond Formation
Devonian Carrabassett Formation (uncertain) (Devonian): Devonian Carrabassett Formation (uncertain)
Precambrian Z Rye Formation (Precambrian): Precambrian Z Rye Formation

Michigan

Dickinson Group, undivided (Late Archean) (Late Archean): Dickinson Group, undivided (Late Archean) - Metavolcanic and metasedimentary rocks in Dickinson County, Mich. From youngest to oldest, consists of Six-Mile Lake Amphibolite, Solberg Schist, and East Branch Arkose.
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).
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.

Minnesota

Migmatitic gneiss, amphibolite, and granite (Middle to Early Archean): Migmatitic gneiss, amphibolite, and granite - Montevideo and Morton Gneisses (3600-3000 m.y.) in the Minnesota River Valley, southwestern Minnesota; McGrath Gneiss (2750 m.y.) east of Mille Lacs Lake; components of Hillman Migmatite southwest of Mille Lacs Lake; and Sartell Gneiss in Stearns County. Inferred to include various younger rocks, including granitoid intrusions in the Hillman Migmatite and pillowed basalt in poorly exposed areas of southwestern Minnesota.
Paragneiss, schist, and amphibolite (Late Archean): Paragneiss, schist, and amphibolite - Amphibolite-facies equivalent of units Amv and Ams; locally includes abundant intrusions of unit Agr.

North Carolina

Alligator Back Formation; Amphibolite (Late Proterozoic): Amphibolite - equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive and extrusive mafic rock; may include metasedimentary rock.
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 (Middle Proterozoic): Amphibolite - unconformity; equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive to extrusive mafic rock; may include metasedimentary rock.
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 (Middle Proterozoic): Amphibolite - unconformity; equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive to extrusive mafic rock; may include metasedimentary rock.
Amphibolite (Cambrian/Late Proterozoic): Amphibolite - equigranular, massive to well foliated, dioritic to basaltic dikes and sills; variably metamorphosed.
Amphibolite (Cambrian/Late Proterozoic): Amphibolite - equigranular, massive to well foliated, dioritic to basaltic dikes and sills; variably metamorphosed.
Amphibolite (Cambrian/Late Proterozoic): Amphibolite - metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, calc-silicate rock, and, rarely, marble. Also includes small 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; Amphibolite (Late Proterozoic): Amphibolite - equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive to extrusive mafic rock; may include metasedimentary rock.
Ashe Metamorphic Suite and Tallulah Falls Formation; Biotite gneiss (Late Proterozoic): Biotite gneiss - interlayered with biotite-garnet gneiss, biotite-muscovite schist, garnet-mica schist, and amphibolite.
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 Gneiss and Schist (Cambrian/Late Proterozoic): Biotite Gneiss and Schist - inequigranular and megacrystic; in places contains garnet; interlayered and gradational with mica schist and amphibolite; includes small masses of granitic rock.
Biotite Gneiss and Schist (Cambrian/Late Proterozoic): Biotite Gneiss and Schist - inequigranular and megacrystic; abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock.
Biotite Gneiss and Schist (Cambrian/Late Proterozoic): Biotite Gneiss and Schist - (Located in the Lilesville granite aureole) inequigranular, locally abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock.
Biotite Gneiss and Schist (Cambrian/Late Proterozoic): Biotite Gneiss and Schist - inequigranular, locally abundant potassic feldspar and garnet; interlayered and gradational with calc-silicate rock, sillimanite-mica schist, mica schist, and amphibolite. Contains small masses of granitic rock.
Biotite Granitic Gneiss (Middle Proterozoic): Biotite Granitic Gneiss - unconformity; pinkish gray to light gray, massive to well-foliated, granitic to quartz monzonitic; includes variably mylonitized orthogneiss and paragneiss, interlayered amphibolite, calc-silicate rock, and marble. Includes granites of the Bryson City area, Straight Fork window, and Elk Park Plutonic Suite.
Blacksburg Formation (Cambrian/Late Proterozoic): Blacksburg Formation - sericite schist, locally with graphite, phyllite with sericite quartzite, banded marble, amphibolite, and minor calc-silicate rock.
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.
Coweeta Group; Amphibolite (Middle/Late Proterozoic): Amphibolite - equigranular, massive to well foliated, interlayered, rarely discordant, metamorphosed intrusive to extrusive mafic rock; may include metasedimentary rock.
Coweeta Group; Biotite Gneiss (Middle/Late Proterozoic): Biotite Gneiss - migmatitic; interlayered and gradational with biotite-garnet gneiss and amphibolite; locally abundant quartz and alumino-silicates. Stratigraphic position uncertain.
Fine-grained Biotite Gneiss (Cambrian/Late Proterozoic): Fine-grained Biotite Gneiss - massive to strongly foliated; minor layers of amphibolite and muscovite schist.
Fine-grained Biotite Gneiss (Cambrian/Late Proterozoic): Fine-grained Biotite Gneiss - strongly foliated; minor layers of amphibolite and muscovite schist.
Fine-grained Biotite Gneiss (Cambrian/Late Proterozoic): Fine-grained Biotite Gneiss - strongly foliated; minor layers of amphibolite and muscovite schist.
Garnet-Mica Schist (Cambrian/Late Proterozoic): Garnet-Mica Schist - interlayered with amphibolite.
Granitic Gneiss (Late Middle Proterozoic): Granitic Gneiss (1192 my) - megacrystic, in places contains amphibolite.
Linville Metadiabase (Late Proterozoic): Linville Metadiabase - metadiabase, greenstone, and amphibolite dikes and sills; massive to schistose.
Megacrystic Biotite Gneiss (Cambrian/Late Proterozoic): Megacrystic Biotite Gneiss - poorly layered to massive; megacrysts of microcline and quartz; local mica schist, amphibolite, and biotite gneiss
Metagraywacke, Amphibolite, and Kyanite Schist (Cambrian/Late Proterozoic): Metagraywacke, Amphibolite, and Kyanite Schist - metagraywacke (biotite gneiss) interlayered and gradational with amphibolite and kyanite schist; minor ultramafic and granitic rock.
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.
Migmatitic Granitic Gneiss (Ordovician/Cambrian): Migmatitic Granitic Gneiss - foliated to massive, granitic to quartz dioritic; biotite gneiss and amphibolite common.

New Hampshire

Littleton Formation, Metabasaltic greenstone or amphibolite (Lower Devonian): Littleton Formation, Metabasaltic greenstone or amphibolite.
Partridge Formation, Interstratified metavolcanic rocks (Middle - Upper Ordovician): Partridge Formation, Interstratified metavolcanic rocks - Chiefly amphibolites, found in southwestern New Hampshire.
Rye Complex (Ordovician? - Late Proterozoic?): Rye Complex - Light-colored to gray schists and gneisses, quartzites, and amphibolites. Variably migmatized and mylonized. Contact with Kittery Formation on west is the Portsmouth Fault.

New Jersey

Amphibolite (Middle Proterozoic): Amphibolite - Gray- to grayish-black, medium-grained amphibolite composed of hornblende and andesine. Some phases contain biotite and (or) clinopyroxene. Ubiquitous and associated with almost all other Middle Proterozoic units. Some amphibolite is clearly metavolcanic in origin, some is metasedimentary, and some appears to be metagabbro.
Amphibolite (Middle Proterozoic): Amphibolite - Medium-grained, very dark gray to black, and foliated; consists of hornblende and andesine. Some exposures exhibit crosscutting bodies of white plagioclase pegmatite
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.
Clinopyroxene-Quartz-Feldspar Gneiss (Middle Proterozoic): Clinopyroxene-Quartz-Feldspar Gneiss - Pinkish-gray- or pinkish-buff-weathering, white to pale-pinkish-white or light-gray, fine- to medium-grained, massive to moderately well-layered gneiss composed of microcline, quartz, oligoclase, clinopyroxene, and trace amounts of epidote, biotite, titanite, and opaque minerals. Commonly interlayered with amphibolite or pyroxene amphibolite.
Diorite (Middle Proterozoic): Diorite - Gray- to tan-weathering, greenish-gray to brownish-gray, medium- to coarse-grained, greasy-lustered, massive diorite containing andesine or oligoclase, clinopyroxene, hornblende, hypersthene, and sparse amounts of biotite and magnetite. Amphibolite layers common.
Hornblende Granite (Middle Proterozoic): Hornblende Granite - Pinkish-gray- to medium-buff-weathering, pinkish-white or light-pinkish-gray, medium- to coarse-grained, gneissoid to indistinctly foliated granite and sparse granite gneiss composed principally of microcline microperthite, quartz, oligoclase, and hornblende. Some phases are quartz syenite or quartz monzonite. Includes small bodies of pegmatite and amphibolite not shown on map. U-Pb age approximately 1,090 Ma (Drake and others, 1991b).
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.
Microperthite Alaskite (Middle Proterozoic): Microperthite Alaskite - Pink- to buff-weathering, light-pinkish-gray or pinkish-white, medium- to coarse-grained, gneissoid to indistinctly foliated granite composed principally of microcline microperthite, quartz and oligoclase. Includes small bodies of amphibolite not shown on map.
Pyroxene Alaskite (Middle Proterozoic): Pyroxene Alaskite - Light-gray- or tan-weathering, greenish-buff to light-pinkish-gray, medium- to coarse-grained, massive, moderately foliated granite composed of mesoperthite to microantiperthite, oligoclase, and quartz. Common accessory minerals are clinopyroxene, titanite and magnetite. Locally includes small bodies of amphibolite not shown on map.
Pyroxene Gneiss (Middle Proterozoic): Pyroxene Gneiss - White- to tan-weathering, greenish-gray, fine- to medium-grained, well-layered gneiss containing oligoclase, clinopyroxene, variable amounts of quartz, and trace amounts of opaque minerals and titanite. Some phases contain scapolite and calcite. Commonly interlayered with pyroxene amphibolite or marble.
Pyroxene Granite (Middle Proterozoic): Pyroxene Granite - Gray- to buff- or white-weathering, greenish-gray, medium- to coarse-grained, massive, gneissoid to indistinctly foliated granite containing mesoperthite to microantiperthite, quartz, oligoclase, and clinopyroxene. Common accessory minerals include titanite, magnetite, apatite, and trace amounts of pyrite. Some phases are monzonite, quartz monzodiorite, or granodiorite. Locally includes small bodies of amphibolite not shown on map.
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.

Nevada

Metamorphic rocks (Early Proterozoic): METAMORPHIC ROCKS-Gneiss and schist and lesser amounts of gneissic granite, pyroxenite, hornblendite, migmatite, pegmatite, and marble.

New York

Amphibolite (Middle Proterozoic): Amphibolite - commonly biotitic; garnetiferous, pyroxenic, in and adjacent to central massif of Adirondacks.
Amphibolite (Middle Proterozoic): Amphibolite - commonly biotitic; garnetiferous, pyroxenic, in and adjacent to Adirondack Highlands.
Amphibolite (Middle Proterozoic): Amphibolite - pyroxenic amphibolite, hornblende gneiss, commonly biotitic, garnetiferous; subordinate calcsilicate rock.
Bedford Gneiss (Ordovician?): Bedford Gneiss - biotite-quartz-plagioclase gneiss and interlayered amphibolite; in part with augen of andesine and microcline.
Biotite and/or hornblende granite gneiss (Middle Proterozoic): Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.
Biotite and/or hornblende granite gneiss (Middle Proterozoic): Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.
Biotite and/or hornblende granite gneiss (Middle Proterozoic): Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. In northwest Adirondacks, grades into Yphg.
Biotite and/or hornblende granite gneiss (Middle Proterozoic): Biotite and/or hornblende granite gneiss - locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.
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 (Middle Proterozoic): Biotite-quartz-plagioclase gneiss - with subordinate biotite granitic gneiss, amphibolite, calcsilicate rock.
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.
Biotite-quartz-plagioclase paragneiss (Middle Proterozoic): Biotite-quartz-plagioclase paragneiss - commonly very low in biotite content, with interbedded feldspathic and biotitic quartzite and amphibolite; sillimanite and garnet common, graphite sporadic.
Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite (Middle Proterozoic): Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite - locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.
Calcitic and dolomitic marble (Middle Proterozoic): Calcitic and dolomitic marble - variably siliceous; in part with calcsilicate rock and amphibolite.
Calcitic and dolomitic marble (Middle Proterozoic): Calcitic and dolomitic marble - variably siliceous; in part with calcsilicate rock and amphibolite.
Calcitic and dolomitic marble (Middle Proterozoic): Calcitic and dolomitic marble - predominantly; variably siliceous; in part with calcsilicate rock and amphibolite.
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.
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.
Hartland Formation (Ordovician?): Hartland Formation - basal amphibolite overlain by pelitic schists.
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 amphibolite and hornblende granitic gneiss (Middle Proterozoic): Interlayered amphibolite and hornblende granitic gneiss.
Leucogranitic (alaskitic) gneiss (Middle Proterozoic): Leucogranitic (alaskitic) gneiss - sodic plagioclase ranges from generally subordinate to locally dominant; locally with biotite, hornblende, pyroxene, garnet, sillimanite, disseminated magnetite; commonly contains metasedimentary layers, amphibolite, migmatite; plagioclase-rich variety is host to magnetite ore bodies in eastern Adirondacks.
Leucogranitic gneiss (Middle Proterozoic): Leucogranitic gneiss - sodic plagioclase ranges from generally subordinate to locally dominant; locally with biotite, hornblende, pyroxene, garnet, sillimanite, disseminated magnetite; commonly contains metasedimentary layers, amphibolite, migmatite; plagioclase-rich variety is host to magnetite ore bodies in eastern Adirondacks.
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.
Metagabbro (Middle Proterozoic): Metagabbro - metagabbro, olivine metagabbro, derived amphibolite.
Metagabbro (Middle Proterozoic): Metagabbro - metagabbro, olivine metagabbro, derived amphibolite.
Quartz-plagioclase gneiss (Middle Proterozoic): Quartz-plagioclase gneiss - may contain pyroxenes, hornblende, biotite; locally interlayered with amphibolite; subordinate biotite mesoperthite gneiss.

Oregon

Amphibolite of Briggs Creek (Mesozoic or Paleozoic) (Paleozoic or Mesozoic): Informally called the "Briggs Creek amphibolite" by Garcia (1976) and by Coleman and others (1976). Consists of amphibolite, micaceous quartzite, quartz schist, and recrystallized manganiferous chert. Includes structurally complex amphibole schist and quartz-rich hornblende gneiss of unknown age exposed at and near Chetco Peak west of Cave Junction (Smith and others, 1982)
Chetco complex of Hotz (1971) (Jurassic) (Late Jurassic): Informally named unit representing island-arc volcanic complex comprised predominantly of igneous and metamorphosed volcanic rocks; includes gabbro, metagabbro, quartz diorite, and amphibolite
May Creek Schist (Paleozoic) (Paleozoic(?) to Jurassic): Layered amphibolite, schist, gneiss, and quartzite. Protolith considered to be of Paleozoic age

Pennsylvania

"Glenarm Wissahickon" formation (Probably lower Paleozoic): "Glenarm Wissahickon" formation - Lithologically similar to oligoclase-mica schist of the Wissahickon Formation (PZw), but also includes lenticular amphibolite bodies having ocean-floor basalt chemistry.

Rhode Island

Blackstone Group - greenstone, amphibolite, serpentinite (Late Proterozoic? or older?): Blackstone Group - greenstone, amphibolite, serpentinite - Dark-green, massive to foliated metamorphosed gabbroic and basaltic rock interlayered with epiclastic rock; local pillow-structures preserved. Consists primarily of epidote, actinolite, chlorite, and plagioclase. Includes rock mapped formerly as Hunting Hill Greenstone.
Esmond Igneous Suite - augen granite gneiss (Late Proterozoic): Esmond Igneous Suite - augen granite gneiss - Pale- to dark-gray, medium- to coarse-grained, granite gneiss characterized by large feldspar porphyroclasts (> 1 cm). Composition ranges from tonalite to granodiorite to quartz monzonite. Composed of sodic plagioclase, quartz, microcline/orthoclase, biotite, opaque minerals; hornblende and epidote common in more mafic types; accessory apatite, sphene, allanite, and zircon; secondary chlorite. Typically massive, but with strong penetrative foliation and lineation defined by major minerals. Commonly contains structurally conformable layers of amphibolite. Includes most rock mapped formerly as Ponaganset Granite Gneiss and Ten Rod Granite Gneiss.
Harmony Group - Absalona Formation (Late Proterozoic? or older?): Harmony Group - Absalona Formation - Gray, medium- to coarse-grained biotite granite gneiss characterized by alkali feldspar porphyroblasts. Consists of biotite, hornblende, quartz, microcline, microperthite, albite, epidote, garnet, and chlorite. Subordinate amounts of quartz-biotite schist, amphibolite, and quartzite occur as layers and isolated bodies.
mica schist (Late Proterozoic? or older?): mica schist - Gray to green, fine-grained, thinly bedded schist consisting of muscovite, biotite, chlorite, and quartz. Locally contains think beds of quartzite, marble, and amphibolite. Includes rock mapped formerly as mica schist of Bristol, chlorite-biotite schist of Tiverton, and mica-chlorite schist of Sakonnet.
Waterford Group - Rope Ferry Gneiss (Late Proterozoic? or older?): Waterford Group - Rope Ferry Gneiss - Light- to dark gray, fine- to medium-grained tonalite gneiss composed of plagioclase, quartz biotite, and hornblende, commonly interlayered with granite gneiss composed of microcline, plagioclase, quartz, biotite, and hornblende; local layers of amphibolite.

South Carolina

Amphibolite and amphibolite gneiss (Paleozoic to Neoproterozoic): Amphibolite and amphibolite gneiss
Amphibolite and interlayered biotite gneiss, hornblende gneiss and minor mica schist (Cambrian or Neoproterozoic): Amphibolite and interlayered gneiss, hornblende gneiss and minor mica schist
Biotite-plagioclase-quartz gneiss and biotite-muscovite schist (Cambrian or Neoproterozoic): Biotite-plagioclase-quartz gneiss and biotite-muscovite schist: variably interlayered, containing subordinate layers of amphibolite and sillimanite-mica schist
Biotite quartz-plagioclase gneiss (Paleozoic or Neoproterozoic): Biotite quartz-plagioclase gneiss: biotite quartz-plagioclase gneiss with minor interlayers of amphibolite gneiss and mica schist
Blacksburg Formation (Neoproterozoic): Blacksburg Formation: metamorphosed sedimentary sequence of interlayered sericite schist and phyllite, sericite quartzite, marble, amphibolite and calc-silicate rock
Burkes Mountain complex, amphibolite (Cambrian and/or Neoproterozoic): Burkes Mountain complex, amphibolite
Garnetiferous mica schist (Cambrian or Neoproterozoic): Garnetiferous mica schist: aluminous muscovite-biotite schist, locally having subordinate amphibolite layers
Latimer complex of Griffin (1979) (Paleozoic or Neoproterozoic): Latimer complex of Griffin (1979): metamorphosed mafic-ultramafic complex consisting mainly of mafic rocks including amphibolite, metagabbro, and greenstone metabasalt
Mafic to intermediate metavolcanics including layered hornblende gneiss and amphibolite (Ordovician to Neoproterozoic): Mafic to intermediate metavolcanics including layered hornblende gneiss and amphibolite
Migmatite paragneiss and schist of Kiokee belt (Cambrian or Neoproterozoic): Migmatite paragneiss and schist of Kiokee belt: migmatitic hornblende-biotite paragneiss having interlayered sillimanite schist and amphibolite
Philson Crossroads complex (undetermined): Philson Crossroads complex: biotite-quartz-feldspar gneiss having interlayers of amphibolite and metagranite
Tallulah Falls Formation, amphibolite (Neoproterozoic): Tallulah Falls Formation: amphibolite
Tallulah Falls Formation, gneiss and schist (Neoproterozoic): Tallulah Falls Formation, gneiss and schist: biotite-quartz-plagioclase gneiss interpreted to be metagraywacke, and interlayered biotite-muscovite schist, garnet-mica schist and amphibolite
Wallhalla metamorphic suite (Cambrian or Neoproterozoic): Wallhalla metamorphic suite: predominately hornblende-plagioclase gneiss and amphibolite, locally having interlayers of biotite-quartz-feldspar gneiss, undivided

South Dakota

Metabasalt (Archean(?) Proterozoic | Paleoproterozoic): Dark-green amphibolite and amphibolite schist. Thickness of individual flows 50-200 ft (15-61 m).
Metabasalt (Proterozoic | Paleoproterozoic): Dark-green amphibolite, actinolite schist, and greenstone. Interflow units consists of graphitic schist, chert, and carbonate- and silicate-facies iron-formation. Thickness of individual flows 50-400 ft (244-1,524 m).
Metagabbro (Proterozoic | Paleoproterozoic): Dark-green sills of amphibolite, actinolite schist, greenstone, and serpentine. Thickness of sills variable, up to 1,000 ft (305 m).
Metamorphosed Siltstone (Proterozoic | Paleoproterozoic): Medium-gray to dark-greenish-gray phyllite, slate, and biotite schist containing minor chert and amphibolite. Locally intruded by thin metagabbro sills. Thickness 1,000-3,000 ft (305-914 m).

Tennessee

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

Carrizo Mountain Group showing metaigneous rocks (preCambrian-Proterozoic): Carrizo Mountain Group showing metaigneous rocks
Carrizo Mountain Group showing metasedimentary rocks (preCambrian-Proterozoic): Carrizo Mountain Group showing metasedimentary rocks
Packsaddle Schist (preCambrian-Proterozoic [Llano]): Packsaddle Schist

Utah

Older Precambrian metamorphic rocks in Logan-Huntsville Allochthon (Proterozoic X)
Older Precambrian metamorphic rocks in Uinta Mountains-Uinta Basin region (Proterozoic W)

Virginia

Alligator Back Formation (Proterozoic Z-Cambrian): Alligator Back Formation - Garnet-mica schist, garnet amphibolite, hornblende granite gneiss
Amphibole Metagabbro (Cambrian): Amphibole Metagabbro
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.
Ashe Formation (Proterozoic Z): Ashe Formation - Biotite gneiss and garnetiferous amphibolite.
Ashe Formation- Amphibolite (Proterozoic Z): Ashe Formation - Amphibolite and garnet amphibolite
Bassett Formation - Amphibolite. (Proterozoic Z-Cambrian): Bassett Formation - Amphibolite.
Diana Mills Complex (Proterozoic Z-Pennsylvanian): Diana Mills Complex - Metamorphosed mafic and ultramafic rocks
Garrisonville Mafic Complex (Proterozoic Z-Cambrian): Garrisonville Mafic Complex - Metamorphosed mafic and ultramafic rocks
Interlayered Mafic and Felsic Metavolcanic Rocks - Amphibolite, hornblende-biotite gneiss, and schist. (Cambrian): Interlayered Mafic and Felsic Metavolcanic Rocks - Amphibolite, hornblende-biotite gneiss, and schist.
Metagabbro (Proterozoic Z-Cambrian): Metagabbro
Ta River Metamorphic Suite (Cambrian): Ta River Metamorphic Suite - Amphibolite gneiss

Vermont

Ammonoosuc Volcanics (Ordovician): Ammonoosuc Volcanics - Fine-grained chloritic and biotitic gneiss and greenstone in areas north of Bellows Falls; biotite gneiss and amphibolite south of Bellows Falls. (Southeastern Vermont).
Gile Mountain Formation, Amphibolite (Devonian): Gile Mountain Formation, Amphibolite - Hornblende-quartz-biotite-chlorite rock.
Gile Mountain Formation, Hall Stream Member (Devonian): Gile Mountain Formation, Hall Stream Member - Highly feldspathic grit, probably volcanic; feldspathic chlorite-ankerite schist and amphibolite; all northeast of Nulhegan River.
Hazens Notch Formation, Belvidere Mountain Amphibolite Member (Cambrian): Hazens Notch Formation, Belvidere Mountain Amphibolite Member - Coarse- to fine-grained hornblende-epidote-albite rock; grades to epidote-chlorite-actinolite-albite greenstone where less metamorphosed. (Northern and Central Vermont).
Hazens Notch Formation, Greenstone and Amphibolite (Cambrian): Hazens Notch Formation, Greenstone and Amphibolite - Chiefly albite-actinolite-chlorite-epidote greenstone; locally hornblende-epidote-chlorite-albite amphibolite. (Northern and Central Vermont).
Hoosac Formation, Amphibolite and Greenstone (Cambrian): Hoosac Formation, Amphibolite and Greenstone - Amphibolite and actinolitic greenstone. (Southern and Central Vermont).
Hoosac Formation, Turkey Mountain Member (Cambrian): Hoosac Formation, Turkey Mountain Member - Amphibolite and actinolitic greenstone characterized by oval, 1/8 to 3/8 inch spots, chiefly of epidote. (Southern and Central Vermont). Discontinuous lenses of metabasalt, informally referred to as Turkey Mountain metabasalt member of Hoosac Formation, actually occur at different stratigraphic positions extending through a stratigraphic distance of 100 to 400 m above base of Hoosac Formation. From type area on Turkey Mountain in Saxtons River quad south to Massachusetts State line, basalts form at least three relatively persistent units (Ratcliffe, 1991). Basalt mapped in northeast corner of this map, above Wilmington thrust system, correlates with type Turkey Mountain. As used here, Turkey Mountain metabasalt member consists of several laterally and vertically discontinuous, nonidentical flows and volcaniclastic deposits including, but not restricted to, type Turkey Mountain Member of Hoosac Formation as used by Doll and others (1961) and by Skehan (1961). They mapped the lower basalts as unnamed greenstones in Hoosac Formation. Turkey Mountain metabasalt member consists of light-green to dark-green epidote-amphibole greenstones and amphibolite metabasalts. Metabasalt varies from massive to very well layered. Finely laminated, quartzose and epidotitic volcaniclastic beds several centimeters thick are interlayered with more massive, strongly foliated, black amphibolite. Where in contact with surrounding metasedimentary rocks, layering within metabasalt and volcaniclastic beds is concordant and gradational with enclosing metasediment. Light-gray or yellowish-greenish-gray, well-laminated quartzite or, less commonly, gritty, pebbly conglomerate 0.5 to 5 m thick marks upper contact with unnamed granofels member of Hoosac Formation. Base of Turkey Mountain metabasalt member in contact with rusty muscovite-albite-biotite schist. Metabasalts probably originated as thin composite basalt lava flows that contained intercalated basaltic volcaniclastic rocks. Age is Late Proterozoic and Early Cambrian (Ratcliffe, 1993).
Missisquoi Formation, Barnard Volcanic Member (Ordovician): Missisquoi Formation, Barnard Volcanic Member - Fine- to medium-grained biotite gneiss, hornblende gneiss, and amphibolite.
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, 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.
Ottauquechee Formation, Greenstone and Amphibolite (Cambrian): Ottauquechee Formation, Greenstone and Amphibolite. The Ottauquechee contains two major units: A black phyllite and the Thatcher Brook Member. The black phyllite contains a previously unreported sub-unit of gray carbonate schist. The Thatcher Brook Member (named in an abstract by Armstrong and others, 1988) is a carbonaceous albitic schist with greenstones and ultramafics. These rocks have previously been included in the Ottauquechee but have never been differentiated from the black phyllite. Member is in fault contact with the silvery green schist of the Pinney Hollow Formation to the west. Age is Cambrian (Ratcliff, in press).
Partridge Formation, Volcanics (Ordovician): Partridge Formation, Volcanics - fine-grained biotite gneiss and amphibolite. (Southeastern Vermont).
Pinney Hollow Formation, Chester Amphibolite Member (Cambrian): Pinney Hollow Formation, Chester Amphibolite Member - Thin-layered, ligniform amphibolite and hornblende schist; includes actinolitic greenstone and greenstone north of Windham. (Southern and Central Vermont).
Pinney Hollow Formation, Ottauquechee, and Stowe Formations, Undifferentiated (Ordovician): Pinney Hollow Formation, Ottauquechee, and Stowe Formations, Undifferentiated - Includes quartz-muscovite-garnet-chlorite-biotite schist, rusty carbonaceous schist, amphibolite, and schistose quartzite. Schist locally contains porphyroblasts of staurolite and kyanite. On flanks of Chester and Athens domes.
Shaw Mountain Formation (Silurian): Shaw Mountain Formation - Quartzite, quartz conglomerate, cummingtonite schist, amphibolite, and quartz-sericite schist with porphyroblasts of biotite and garnet.
Stowe Formation, greenstone and amphibolite (Cambrian-Ordovician): Stowe Formation, greenstone and amphibolite - Epidote-albite-chlorite rocks contain actinolite and hornblende where more metamorphosed.
Waits River formation, Standing Pond Volcanic Member (Devonian): Waits River formation, Standing Pond Volcanic Member - Amphibolite, garnet amphibolite, coarse garnet schist with fasciculitic hornblende, and hornblende maculite; contains pillow lavas near St. Johnsbury and passes eastward into actinolitic greenstone and greenstone south of Windsor.

Washington

Lower Paleozoic rocks, undivided (Paleozoic; likely Ordovician): Predominantly gneiss and schist in northern Ferry County. Quartzite, partly interbedded with dolomitic and calcitic marble, lime-silicate gneiss, and amphibolite; including in places forsterite marblean diopside marble, quartz-biotite-sillimanite schist and sillimanite-orthoclase gneiss in northeastern Ferry County. Quartzite with overlying limestone in southeastern Stevens County. Some upper Paleozoic and Precambrian rocks may be included.
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-Middle Jurassic volcanic rocks, undivided (Early Cretaceous-Late Jurassic): Predominantly greenstone and spilitic volcanic rocks; includes some slate, argillite, and graywacke.
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-Tertiary ultrabasic intrusive rocks (Late-Jurassic): Peridotite and pyroxenite; generally altered partly or completely to serpentine. Includes serpentinite and saxonite on Sumas Mountain, Whatcom County.
Pre-Tertiary volcanic rocks, undivided (Probably mostly Jurassic): Andesite and basalt flows, and greenstone; includes minor interbedded limestone, arkose, quartzite, and chert beds.
Pre-Upper Jurassic gneiss (Mostly Cretaceous): Biotite, quartz diorite, trondhjemite, and hornblende gneisses, many of which are migmatitic; includes small granitic bodies locally. Small areas of mica schist, marble, amphibolite, and lime-silicate rocks in Entiat Mountains area of Chelan County.
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.

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)
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.

West Virginia

Catoctin Formation (Cambrian/Precambrian): Catoctin Formation - predominantly a greenstone. Basic lava flows, schist and gneiss, containing chlorite, plagioclase, amphibolite, and epidote. Includes minor quantities of arkose and thin clastics. Western subsurface extension presently unknown.

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