Geologic units containing mica schist

Earth material > Metamorphic rock > Schist

Mica schist

A schist whose essential constituents are mica and quartz, and whose schistosity is mainly due to the parallel arrangement of mica flakes.

This category is also used for biotite schist.

Subtopics:
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Alabama - California - Colorado - Connecticut - Delaware - Georgia - Idaho - Massachusetts - Maryland - Michigan - North Carolina - New Hampshire - Oregon - Pennsylvania - Rhode Island - South Carolina - Tennessee - Texas - Virginia - Vermont

Alabama

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.
Emuckfaw Group; Glenloch Schist (Precambrian to Paleozoic): Glenloch Schist - graphite-garnet-muscovite schist with interlayered metagraywacke.
Higgins Ferry Group (Precambrian to Paleozoic): Higgins Ferry Group - thinly layered coarse to fine-grained biotite-feldspar-quartz gneiss, sericite-feldspar-muscovite schist, +/- biotite +/- garnet-muscovite schist, and biotite-garnet feldspathic gneiss; locally common pegmatites.
Opelika Complex; Auburn Gneiss (Precambrian to Paleozoic): Auburn Gneiss - fine-grained biotite-oligoclase gneiss intermixed with coarse-grained muscovite-biotite schist; locally contains muscovite-rich pegmatite.
Opelika Complex; Auburn Gneiss, Unnamed unit (Precambrian to Paleozoic): Opelika Complex; Auburn Gneiss, Unnamed unit - unnamed unit comprised of masses of medium- to coarse-grained muscovite-biotite schist, locally garnetiferous; grades into oa.
Opelika Complex; Loachapoka Schist (Precambrian to Paleozoic): Loachapoka Schist - muscovite-quartz schist; locally contains biotite-garnet-muscovite schist, many layers conatin sillimanite (northeast of Mount Jefferson, Lee County); kyanite (west of Mount Jefferson); locally muscovite-rich schist and quartzite common.
Poe Bridge Mountain Group (Precambrian to Paleozoic): Poe Bridge Mountain Group - coarse to fine-grained feldspathic graphite schist, +/- staurolite +/- kyanite +/- sillimanite-muscovite-biotite schist, and garnet-biotite-muscovite schist, and gneiss; locally common pegmatites. Rocks in the area of Turkey Heaven Mountain in Cleburne and Randolph Counties that are here assigned to the Poe Bridge Mountain Group also have been interpreted as part of the Wedowee Group.
Wacoochee Complex; Halawaka Schist (Precambrian to Paleozoic): Halawaka Schist - feldspathic muscovite-biotite schist and quartz-diorite gneiss; locally contains lenses of muscovite-graphite schist and amphibolite; commonly cut by feldspathic veins and pegmatites.

California

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 4 (El Paso Mountains) (Paleozoic): Schists of various types; mostly Paleozoic or Mesozoic age; some Precambrian.

Colorado

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

Connecticut

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.
Fitch Formation (Silurian): Fitch Formation - Gray, fine- to medium-grained calc-silicate rock, composed of quartz, biotite, calcite, actinolite, diopside, microcline, and locally garnet, scapolite, or epidote, interlayered with two-mica schist.
Hebron Gneiss (Silurian and Ordovician): Hebron Gneiss - Interlayered dark-gray, medium- to coarse-grained schist, composed of andesine, quartz, biotite, and local K-feldspar, and greenish-gray, fine- to medium-grained calc-silicate rock, composed of labradorite, quartz, biotite, actinolite, hornblende, and diopside, and locally scapolite. Local lenses of graphitic two-mica schist.
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.
Quartzite unit [in Scotland Schist] (Devonian or Silurian or both): Quartzite unit [in Scotland Schist] - Quartzite, generally micaceous, interlayered with mica schist.
Shelton Member [of Trap Falls Formation] (Middle or Lower Ordovician): Shelton (white gneiss) Member [of Trap Falls Formation] - White, light-gray, or buff, fine- to medium-grained, generally well foliated granitic gneiss, composed of sodic plagioclase, quartz, microcline, muscovite, and garnet (in tiny almost ubiquitous grains), also commonly minor biotite; generally interlayered with mica schist, biotite gneiss, and calc-silicate rock. Thought to be metavolcanic equivalent of unit Og. Shelton Member of Trap Falls Formation (Rodgers, 1985) is here referred to as Shelton muscovite granite. On the basis of field and laboratory studies, Ansonia, Beardsley, Pumpkin Ground, and Shelton gneisses, previously considered stratigraphic units, are reinterpreted as plutonic. Shelton is a foliated, medium-grained, garnet-bearing muscovite leucogranite with a conspicuous white color and abundant garnets. Age of crystallization determined from U-Pb garnet analysis is 380+/-3 Ma (Middle Devonian). Southeast margin of the Shelton is in contact with the Trap Falls Formation (Sevigny and Hanson, 1993).
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 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.
Yantic Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician): Yantic Member [of Tatnic Hill Formation] - Medium- to dark-gray, fine- to medium-grained schist, composed of quartz, oligoclase, biotite, and muscovite, some layers with garnet, staurolite, and kyanite or garnet and sillimanite, local epidote, or K-feldspar; some layers of rusty-weathering graphitic, pyrrhotitic, two-mica schist.

Delaware

Wissahickon Schist (Paleozoic): Wissahickon Schist - Dense micaceous schist, gneiss and migmatite.

Georgia

Amphibolite/ Mica Schist/ Biotitic Gneiss (Precambrian-Paleozoic): Amphibolite/ Mica Schist/ Biotitic Gneiss
Amphibolitic Schist/ Amphibolite-Metagraywacke/ Mica Schist (Precambrian-Paleozoic): Amphibolitic Schist/ Amphibolite-Metagraywacke/ Mica Schist
Biotite Gneiss/ Mica Schist (Age not given): Biotite Gneiss/ Mica Schist
Biotitic Gneiss / Mica Schist/ Amphibolite (Precambrian-Paleozoic): Biotitic Gneiss / Mica Schist/ Amphibolite
Button Mica Schist (Precambrian-Paleozoic): Button Mica Schist
Calcareous mica schist/ Micaceous marble/ Mica schist (Precambrian-Paleozoic): Calcareous mica schist/ Micaceous marble/ Mica schist
Garnet Mica Schist (Precambrian-Paleozoic): Garnet Mica Schist
Garnet Mica Schist/ Amphibolite (Precambrian-Paleozoic): Garnet Mica Schist/ Amphibolite
Garnet Mica Schist/ Gneiss (Precambrian-Paleozoic): Garnet Mica Schist/ Gneiss
Metagraywacke/ Mica Schist (Precambrian-Paleozoic): Metagraywacke/ Mica Schist
Metagraywacke/ Mica Schist/ Calc-silicate Gneiss (Precambrian-Paleozoic): Metagraywacke/ Mica Schist/ Calc-silicate Gneiss
Metagraywacke/ Mica Schist-Quartzite/ Amphibolite (Precambrian-Paleozoic): Metagraywacke/ Mica Schist-Quartzite/ Amphibolite
Mica Schist (Precambrian-Paleozoic): Mica Schist
Mica Schist/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Amphibolite
Mica Schist/ Gneiss (Precambrian-Paleozoic): Mica Schist/ Gneiss
Mica Schist/ Gneiss/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Gneiss/ Amphibolite
Mica Schist/ Metasiltstone (Precambrian-Paleozoic): Mica Schist/ Metasiltstone
Mica Schist/ Quartzite/ Gneiss/ Amphibolite (Precambrian-Paleozoic): Mica Schist/ Quartzite/ Gneiss/ Amphibolite
Quartzite/ Mica Schist (Precambrian-Paleozoic): Quartzite/ Mica Schist
Quartzite/ Mica Schist/ Amphibolite (Precambrian-Paleozoic): Quartzite/ Mica Schist/ Amphibolite
Quartz Mica Schist/ Hornblende Schist/ Biotitic Gneiss (Precambrian-Paleozoic): Quartz Mica Schist/ Hornblende Schist/ Biotitic Gneiss
Undifferentiated pelitic rocks (Precambrian-Paleozoic): Undifferentiated pelitic rocks, includes mica schists, metasiltstones, metaconglomerates, and metagraywackes

Idaho

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.
Garnet-mica schist, gneiss, and quartzite; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Late to Early Proterozoic): Precambrian high-grade metamorphic rock; metasediment; Kyanite-sillimanite-garnet-mica schist and gneiss; minor quartzite
High-grade metasedimentary biotite schist, biotite gneiss, and calc-silicate gneiss; Middle Proterozoic northern Belt province near Idaho batholith (Middle Proterozoic): Precambrian high-grade metamorphic rock; kyanite-sillimanite calc-silcate bearing schist and gneiss; scapolite common
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, and calc-silcicate rock; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Proterozoic): Precambrian high-grade metamorphic rock; metasediment; kyanite-sillimanite calc-silicate schist and gneiss, scapolite common
Mica schist, quartzite, gneiss, and amphibolite; Late to Early Proterozoic high-grade metasedimentary rocks (subunits are ZXmhs, ZXmhq, and ZXmhc); trans-Idaho metamorphic province (Proterozoic): Precambrian high-grade metamorphic rock; metasediment
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 and biotite schist in fault contact; Middle Proterozoic metasedimentary rocks; southern Belt province (Middle Proterozoic): Intermediate Precambrian age metasediments; dominantly quartzite with minor micaceous layers and mica schists of northern Idaho
Quartzite and muscovite schist; Middle Protrerozoic metasedimentary rocks of the Ravalli Group; northern Belt province (Middle Proterozoic): Intermediate Precambrian age metasediments; dominantly quartzite with minor micaceous layers and mica schists of northern Idaho.
Quartzite, mica schist, and calc-silicate rock; Proterozoic high-grade metasedimentary rocks; trans-Idaho metamorphic province (Proterozoic): Precambrian, high-grade metamorphic rock; metasediments; kyanite-sillimanite schist, and micaceous quartzite
Quartzite, mica schist, and marble; Cambrian and Late Proterozoic metasedimentary rocks; south-central Idaho, Albion-Range metamorphic core complex (Cambrian to Late Proterozoic): Schist, quartzite and other metasediments of probable Lower Ordovician to Cambrian age.
Quartzite, siltite, argillite, and mica schist; Middle Proterozoic Lemhi Group; southern Belt province (Middle Proterozoic): Intermediate Precambrian sediments, feldspathic quartzite and siltstone of southern Idaho.
Schist, phyllite, quartzite, and calc-silicate rock; Middle Proterozoic metasedimentary rocks of Wallace Formation; northern Belt province (Middle Proterozoic): Intermediate Precambrian age metasediments; generally low-to-medium grade; carbonate bearing argillite and siltite of northern Idaho.

Massachusetts

Berwick Formation (Silurian): Berwick Formation - Thin- to thick-bedded metamorphosed calcareous sandstone, siltstone, and minor muscovite schist. In New Hampshire: Used as Berwick Formation of Merrimack Group. Consists of purple biotite-feldspar granofels or schist. Contains interbeds of calcsilicate granofels and minor metapelites. Includes Gove Member, mapped separately. Stratigraphic sequence with respect to Eliot Formation is uncertain. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).
Berwick Formation (Silurian): Berwick Formation - Mica schist. In New Hampshire: Used as Berwick Formation of Merrimack Group. Consists of purple biotite-feldspar granofels or schist. Contains interbeds of calcsilicate granofels and minor metapelites. Includes Gove Member, mapped separately. Stratigraphic sequence with respect to Eliot Formation is uncertain. Age of all formations in Merrimack Group changed to Ordovician(?) to Silurian(?) based on isotopic age determinations of approx 440 and 420 Ma from detrital zircons from Berwick by J.N. Aleinikoff (oral commun., 1994) (Lyons and others, 1997).
Blackstone Group (Proterozoic Z): Blackstone Group - Mica schist and phyllite - Includes Mussey Brook Schist and Sneech Pond Schist.
Clough Quartzite (Upper Silurian): Clough Quartzite - Quartz-pebble conglomerate, quartzite, and minor mica schist and calc-silicate rocks. Fossils at Bernardston are similar to those at Croyden Mountain, New Hampshire which indicate late Llandoverian age. Parts of the Littleton and Partridge Formations, and Clough Quartzite in MA are here reassigned to the Rangeley Formation [here geographically extended to MA]. The four mapped areas of Clough Quartzite in the Amherst area west of the Connecticut Valley border fault are now interpreted as conglomerate lenses in the Rangeley. Clough is considered the key stratigraphic unit in Bronson Hill anticlinorium because 1) it is dominated by distinctive, readily recognizable rock types, 2) where present, it is base of Silurian-Devonian sequence, resting with detectable unconformity on older rocks, and 3) it contains late Llandoverian fossils at several localities in western NH and adjacent VT, and at Bernardston, MA. Consists mostly of quartz-pebble conglomerate in which pebbles are typically deformed; other lithologies are quartz grit or white to pink, well-bedded quartzite. Locally contains some mica schist beds. On the MA State bedrock geologic map (Zen and others, 1983), thickness is locally exaggerated because at many localities, the unit was only a few meters or less thick and could not be shown at a scale of 1:250,000. Maximum thickness is 200 m on west limb of Northfield syncline. Unconformably overlies Fourmile Gneiss in Pelham dome and in Kempfield anticline, or Ammonoosuc Volcanics over most gneiss domes. Partridge Formation occurs along Clough-Ammonoosuc contact as lenses in many areas (Hatch and others, 1988).
Cobble Mountain Formation (Middle Ordovician): Cobble Mountain Formation - Rusty-weathering mica schist.
Cobble Mountain Formation (Middle Ordovician): Cobble Mountain Formation - Rusty-weathering mica schist; thin (15 cm or less) beds of gneiss.
Cobble Mountain Formation (Middle Ordovician): Cobble Mountain Formation - Brown- or rusty-weathering thin-bedded feldspathic gneiss and mica 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.
Dalton Formation (Lower Cambrian and Proterozoic Z): Dalton Formation - Orangish-gray, gray, and light-greenish-gray muscovite-quartz schist and interlayered feldspathic quartzite and quartz conglomerate; minor beds of rusty albitic schist.
Dalton Formation (Lower Cambrian and Proterozoic Z): Dalton Formation - Tan to orangish-tan quartz and gneiss cobble and pebble conglomerate, rusty feldspathic schist, and lustrous greenish-gray muscovite quartz schist.
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.
Fitchburg Complex (Lower Devonian or younger): Fitchburg Complex -Dark-gray, strongly foliated biotite granodiorite to tonalite gneiss; resembles Dht; intrudes and contains inclusions of Dl, some mappable; locally cut by sills identical to Dfgrg.
Fitchburg Complex (Lower Devonian or younger): Fitchburg Complex - Light-gray, strongly foliated biotite-muscovite granite to granodiorite gneiss; common small to very large inclusions of Dl, some mapped separately.
Fitchburg Complex (Lower Devonian or younger): Fitchburg Complex - Dfgd containing many zones of foliated biotite-muscovite granite gneiss and inclusions of mica schist and feldspathic granulite.
Fitch Formation (Upper Silurian): Fitch Formation - Sulfidic mica schist. Although the text and figures of this report show the Fitch as Silurian, a footnote [added just before this report went to press] cites a change in age from Silurian to Early Devonian based on conodonts found at the Bernardston, MA, locality, as reported in Elbert and others (1988). In Bronson Hill anticlinorium in MA, Fitch occurs as lenses between Clough Quartzite and Littleton Formation. Most common rock types in MA are gray, massive to weakly bedded, quartz-labradorite-biotite granulite containing a moderate amount of some combination of calc-silicate minerals (calcic amphibole, zoisite or clinozoisite, diopside, sphene, and microcline); commonly interbedded with biotite-free granulite that contains same calc-silicate minerals. One small exposure consists of nearly pure calcite marble. Larger lenses of Fitch consist of varieties of schist, similar to Partridge Formation. Best exposures are in low hills west of village of Orange, northeast of junction of MA Hwys 2A and 78. As shown on MA State bedrock geologic map, Fitch everywhere overlies Clough Quartzite and is never in contact with Partridge. Fossils dating the Fitch as Pridolian (Harris and others, 1983) are all from Littleton, NH, area [however, see mention of footnote, above]. [Papers presented as chapters in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to MA State bedrock geologic map of Zen and others (1983) at scale of 1:250,000.] (Hatch and others, 1988).
Hoosac Formation (Lower Cambrian and Proterozoic Z): Hoosac Formation - Rusty-brown to dark-gray, albite-spotted muscovite-biotite schist or gneiss, with interlayered black garnet-biotite-albite-quartz schist near base; interfingers with Dalton Formation.
Hoosac Formation (Lower Cambrian and Proterozoic Z): Hoosac Formation - Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.
Hoosac Formation (Lower Cambrian and Proterozoic Z): Hoosac Formation - Greenish chlorite-albite-magnetite-sericite-quartz schist and granofels.
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.
Moretown Formation (Middle Ordovician or older): Moretown Formation - Buff to gray, medium- to coarse-grained, poorly bedded mica-rich schist showing dark-green chlorite clots. Some pinstriped granofels.
Moretown Formation (Middle Ordovician or older): Moretown Formation - Light- to medium-gray, rusty, carbonaceous quartz-muscovite schist.
Oakdale Formation (Silurian): Oakdale Formation - Metamorphosed thin-bedded, pelitic and calcareous siltstone and muscovite schist, probably low-grade equivalent of Paxton Formation. The Oakdale Formation is here revised to include strata previously mapped in CT and adjacent MA as the Hebron Formation and the Scotland Schist. The Scotland Member (Pease, 1980) is renamed the Scotland Schist Member of the Oakdale. The Oakdale is a homogeneous, calcareous metasiltstone at the base of a thick stratigraphic sequence in a geosyncline terrane and extends from NH to the Honey Hill fault in eastern CT. In central eastern CT it underlies the Hebron Formation; in northeast CT and adjacent MA it underlies conformably the Dudley Formation of the Paxton Group; in central MA it underlies the Paxton Group undivided. The lower part of the Oakdale is cut out along the Clinton-Newbury fault zone. Thickness in type area is about 1500 m. Correlative with the Gove Member of the Berwick Formation in NH and the Gonic Formation in ME. Age is Late Proterozoic(?) based on intrusion of 440 Ma Hedgehog Hill gneiss in the upper part of the Brimfield Group at the top of the stratigraphic sequence, and an age of 1188 Ma for detrital zircons from the Paxton in north-central MA (Pease, 1989).
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.
Paxton Formation (Silurian): Paxton Formation - Sulfidic mica schist where mapped separately. 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).
Tatnic Hill Formation (Ordovician or Proterozoic Z): Tatnic Hill Formation - Yantic Member - Gray mica schist.
Washington Gneiss (Proterozoic Y): Washington Gneiss - Rusty-weathering, muscovite-biotite-sillimanite and/or kyanite-garnet schist; blue-quartz ribbed conglomerate, interlayered garnet-plagioclase-quartz metadacite.

Maryland

Marburg Schist (Late Precambrian (?)): Marburg Schist - Bluish-gray to silvery-green, fine-grained, muscovite-chlorite-albite-quartz schist; intensely cleaved and closely folded; contains interbedded quartzites.
Setters Formation (Late Precambrian (?)): Setters Formation - Upper member: Feldspathic mica schist and mica gneiss; total thickness 200 to 500 feet. Middle member: Impure quartzite interstratified with thin beds of mica schist; total thickness 200 to 500 feet. And Lower member: Medium-grained, feldspathic mica schist; locally granitized; total thickness 200 to 500 feet.

Michigan

Biotite schist (Lake Archean) (Late Archean): Biotite schist (Lake Archean) - Quartz-plagioclase-biotite schist of probably intermediate volcanic protolith in area south of Gogebic Range

North Carolina

Alligator Back Formation; Mica schist and phyllite (Late Proterozoic): Mica schist and phyllite - laminated to thin layered; interlayered with minor biotite-muscovite gneiss and amphibolite.
Amphibolite (Cambrian/Late Proterozoic): Amphibolite - metamorphosed mafic extrusive and intrusive rock; includes hornblende gneiss, thin layers of mica schist, and small nonlayered masses of metadiorite and metagabbro.
Amphibolite (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; 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; Metagraywacke (Late Proterozoic): Metagraywacke - foliated to massive, locally conglomeratic; interlayered and gradational with mica schist, muscovite-biotite gneiss, and rare graphitic schist.
Ashe Metamorphic Suite and Tallulah Falls Formation; Mica schist (Late Proterozoic): Mica schist - locally sulfidic and graphitic; minor interlayered mica gneiss and amphibolite.
Ashe Metamorphic Suite and Tallulah Falls Formation; Muscovite-biotite gneiss (Late Proterozoic): Muscovite-biotite gneiss - locally sulfidic; interlayered and gradational with mica schist, minor amphibolite, and hornblende gneiss.
Banded Gneiss (Cambrian/Late Proterozoic): Banded Gneiss - interlayered with calc-silicate rock, metaconglomerate, amphibolite, sillimanite-mica schist, and granitic rock.
Biotite 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 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 - 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, 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.
Brasstown Formation (Late Proterozoic): Brasstown Formation - cross-biotite schist; includes micaceous quartzite in lower part.
Felsic Mica Gneiss (Cambrian/Late Proterozoic): Felsic Mica Gneiss - interlayered with biotite and hornblende gneiss and schist.
Felsic Mica Gneiss (Cambrian/Late Proterozoic): Felsic Mica Gneiss - interlayered with graphitic mica schist and mica-garnet schist, commonly with kyanite; minor hornblende gneiss.
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.
Fine-grained Biotite Gneiss (Cambrian/Late Proterozoic): Fine-grained Biotite Gneiss - massive to strongly foliated; minor layers of amphibolite and muscovite schist.
Garnet-Mica Schist (Cambrian/Late Proterozoic): Garnet-Mica Schist - interlayered with amphibolite.
Lineated Felsic Mica Gneiss (Cambrian/Late Proterozoic): Lineated Felsic Mica Gneiss - white to pink, with strong lineation of muscovite-biotite streaks and prismatic quartz aggregates; planar foliation and layering weak; minor mica schist and hornblende gneiss.
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 and Muscovite-Biotite Schist (Cambrian/Late Proterozoic): Metagraywacke and Muscovite-Biotite Schist - metagraywacke (biotite gneiss) interlayered and gradational with muscovite-biotite schist; minor marble 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.
Ocoee Supergroup, Great Smokey Group; Copperhill Formation (Late Proterozoic): Copperhill Formation - metagraywacke, massive, graded bedding common; includes dark-gray slate, mica schist, and nodular calc-silicate rock.
Ocoee Supergroup, Great Smokey Group; Dean Formation (Late Proterozoic): Dean Formation - sericite schist with cross-biotite, staurolite, and garnet porphyroblasts; interbedded metagraywacke and quartz-pebble metaconglomerate.
Ocoee Supergroup, Great Smokey Group; Metasandstone, Metagraywacke, Metasiltstone, and Mica Schist (Late Proterozoic): Metasandstone, Metagraywacke, Metasiltstone, and Mica Schist - beds and lenses of calc-silicate rock locally abundant; garnet, staurolite, and cross-biotite porphyroblasts common in fine-grained layers. Includes Hughes Gap and Hothouse formations in southern area; Horse Branch Member of Ammons Formation and Grassy Branch Formation in northern area.
Quartzite and Quartz-Muscovite Schist (Cambrian/Late Proterozoic): Quartzite and Quartz-Muscovite Schist - garnet, andalusite, kyanite, or sillimanite occur locally.

New Hampshire

Clough Quartzite (Lower Silurian (upper Llandoverian)): Clough Quartzite - Orthoquartzite, quartz metaconglomerate, muscovite schist, minor polymictic metaconglomerate. Disconformable below Fitch Formation and unconformable on Ordovician formations. Equivalent, in part, to member C of Rangeley Formation of Maine. Fossiliferous.
Fitch and Clough Formations, undivided (Silurian): Fitch and Clough Formations, undivided.
Massabesic Gneiss Complex (Late Proterozoic): Massabesic Gneiss Complex - Quartzose-feldspathic gneiss and biotite schists (locally rusty), granofels, and cal-silicate rocks closely intruded by, and grading into, a pink gneissic granite (623 Ma) that produced a migmatite.
Merrimack Group, Berwick Formation, Gove Member (Ordovician? - Silurian?): Merrimack Group, Berwick Formation, Gove Member - White muscovite schist. Equivalent to the Gonic Formation of Hussey (1962).
Merrimack Group, Eliot Formation (Ordovician? - Silurian?): Merrimack Group, Eliot Formation - Gray to green phyllite, calcareous quartzite, quartz-mica schist, and well-bedded calc-silicate.

Oregon

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.
Marburg Schist (Probably lower Paleozoic): Marburg Schist - Gray-green phyllite, mica-chlorite schist, and conglomerate.
Setters Quartzite (Probably lower Paleozoic): Setters Quartzite - Includes white feldspathic quartzite, gray mica gneiss, and mica schist.
Wissahickon Formation (Probably lower Paleozoic): Wissahickon Formation - Includes oligoclase-mica schist, some hornblende gneiss, some augen gneiss, and some quartz-rich and feldspar-rich members due to various degrees of granitization.

Rhode Island

Blackstone Group - epidote and biotite schist (Late Proterozoic? or older?): Blackstone Group - epidote and biotite schist - Green to gray, fine-grained, massive to thinly-bedded mica schist, quartzite, and marble. Schist consists of quartz plus chlorite, muscovite, and/or biotite. Includes rock mapped formerly as Sneech Pond Schist, Mussey Brook Schist, and marble.
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.
Plainfield Formation (Late Proterozoic? or older?): Plainfield Formation - Pale-tan to gray, fine-grained quartzite, and pale- to medium-gray quartz-mica schist. Quartzite is massive to layered (bedded?). Includes Plainfield Formation and some rock mapped formerly as Blackstone Series.

South Carolina

Garnetiferous mica schist (Cambrian or Neoproterozoic): Garnetiferous mica schist: aluminous muscovite-biotite schist, locally having subordinate amphibolite layers
Little River Sequence, metasedimentary rocks (Cambrian or Neoproterozoic): Little River Sequence, metasedimentary rocks: white-mica schist and phyllite, metatuff, quartz-muscovite schist, and minor quartzite
Sillimanite-mica schist and muscovite-biotite schist (Cambrian or Neoproterozoic): Sillimanite-mica schist and muscovite-biotite schist: thin to thick layered sillimanite-mica schist and sillimanite-bearing muscovite-biotite schist

Tennessee

Cranberry Granite (Precambrian): Cranberry Granite - Complex of intertonguing rock types including migmatite, granitic gneisses, monzonite, quartz diorite, greenstone, mica and hornblende schists, abundant granitic pegmatite.
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 metasedimentary rocks (preCambrian-Proterozoic): Carrizo Mountain Group showing metasedimentary rocks
Packsaddle Schist (preCambrian-Proterozoic [Llano]): Packsaddle Schist
Valley Spring Gneiss (preCambrian-Proterozoic): Valley Spring Gneiss

Virginia

Alligator Back Formation (Proterozoic Z-Cambrian): Alligator Back Formation - Garnet-mica schist, garnet amphibolite, hornblende granite gneiss
Arvonia Formation - Porphyroblastic garnet-biotite schist (Ordovician): Arvonia Formation - Porphyroblastic garnet-biotite schist
Ashe Formation -Mica schist or phyllite (Proterozoic Z): Ashe Formation - Mica schist or phyllite
Fork Mountain Formation (Proterozoic Z-Cambrian): Fork Mountain Formation - Quartzose mica schist, garnet-biotite gneiss, calc-silicate quartzite, and melange.
Metavolcanic and Metasedimentary Rocks - Felsic metatuff, mica schist, and gneiss. (Cambrian): Metavolcanic and Metasedimentary Rocks - Felsic metatuff, mica schist, and gneiss.
Muscovite Schist and Gneiss (Proterozoic Y): Muscovite schist and gneiss

Vermont

Albee Formation (Ordovician): Albee Formation - Massive, gray, white-weathered quartzite and feldspathic quartzite interbedded with greenish-gray slate, phyllite, feldspthic phyllite and quartzose argillaceous phyllite. Micaceous quartzite, quartz-mica schist, mica schist and hornfels contining porphyroblasts of biotite, garnet, staurolite and sillimanite in the vicinity of granitic plutons. Soda-rhyolite tuff occurs locally. Micaceous quartzite characterized by thin, schistose "pinstripe" partings is common in many areas.
Cavendish Formation, Readsboro Member (Cambrian?): Cavendish Formation, Readsboro Member - Quartz-muscovite schist containing biotite or chlorite and characterized by conspicuous porphyroblasts of sodic plagioclase; less commonly quartz-muscovite-paragonite schist containing chlorite, garnet, or chloritoid, or, in Chester dome, quartz-muscovite-paragonite schist containing garnet, staurolite, and locally kyanite (Gassetts schist). The Cavendish Formation is reinstated and considered part of the Mount Holly Complex in VT. Usage follows Thompson (1950), but is extended to include some rocks on Star Hill, including inner and outer cover rocks assigned by Downie (1982) to Hoosac and Pinney Hollow Formations. Formation is divided into four map units: calc-silicate rock and gneiss, marble, feldspathic schist or granofels, and the Gassetts Schist Member. The Cavendish correlates with the Wilcox Formation of the Mount Holly Complex in the Green Mountain massif, and therefore, is of Middle Proterozoic age (Ratcliffe, in press).
Clough Formation (Silurian): Clough Formation - Quartzite, quartz-conglomerate, and mica schist; lenses of fossiliferous calcareous quartzite in upper part. (Southeastern Vermont).
Clough Formation (Silurian): Clough Formation - Boulders, cobbles, pebbles and angular fragments of quartzite, micaceous quartzite, and gray mica schist in matrix of dark gray quartz-mica schist or quartzite; schist commonly contains porphyroblasts of biotite, less commonly garnet. (Northeastern Vermont).
Fitch Formation (Silurian): Fitch Formation - Quartz-plagioclase-biotite granulite; actinolite-diopside granulite; impure limestone and dolomite; mica schist; the carbonate-rich beds are typically an inch or two thick and segmented so as to give the weathered outcrop a characteristic pitted appearance. (Southeastern Vermont).
Gile Mountain Formation (Devonian): Gile Mountain Formation - Gray quartz-muscovite phyllite or schist, interbedded and intergradational with gray micaceous quartzite (graywacke northeast of Nulhegan River), calcareous mica schist, and, locally, quartzose and micaceous crystalline limestone like that of the Waits River formation. The phyllite and schist commonly contain porphyroblasts of biotite, garnet, or staurolite, and locally kyanite, andalusite, or sillimanite. Used as Early Devonian Gile Mountain Formation. Generally consists of gray to tan metawacke and schist or phyllite, gradational into its Meetinghouse Slate Member, but much more thickly bedded and less pelitic. Contains minor metavolcanic lentils. Unnamed metavolcanic member is possibly equivalent to Putney Volcanics of southeastern VT. Separately mapped interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone, and minor marble and quartzite, resembles Waits River Formation of VT. Meetinghouse Slate Member consists of gray to black phyllite and silty metasandstone turbidite. Report includes geologic map, cross sections, correlation chart, and four 1:500,000-scale derivative maps (Lyons and others, 1997).
Hazens Notch Formation (Cambrian): Hazens Notch Formation - Interbedded carbonaceous and noncarbonaceous quartz-sericite-albite-chlorite schist; grades to quartzite and gneiss. (Northern and Central Vermont). According to author, the name Hazens Notch is a big problem in VT stratigraphic nomenclature. In northern VT, it consists of carbonaceous and non-carbonaceous schist associated with ultramafics, mafic schists, and blueschists, while in the Camels Hump quad, it is considered to be strictly a carbonaceous albitic schist with associated mafic schist. The use of the name Hazens Notch is not recommended for the white albitic schist of the Fayston-Buels Gore area. Those rocks are here assigned to the newly named Fayston Formation (Walsh, 1992).
Hazens Notch Formation, sericite-quartz-chlorite-albite-magnetite schist (Cambrian): Hazens Notch Formation, sericite-quartz-chlorite-albite-magnetite schist - near Hyde Park. (Northern and Central Vermont).
Hoosac Formation (Cambrian): Hoosac Formation - Quartz-sericite-albite-biotite-chlorite schist characterized by albite porphyroblasts - biotite and garnet porphyroblasts common southward; locally carbonaceous. (Southern and Central Vermont). First revision is restriction of Tyson Formation and its replacement by Hoosac Formation in this quad. Cover rocks overlying basement of West River antiformal sheath fold (in hanging-wall of Ball Mountain thrust) consist of albitic schist locally containing pods of white dolomite and discontinuous basal beds of vitreous quartzite and interbedded dolomite as much as 15 m thick. These rocks were previously mapped as Tyson Formation by Doll and others (1961, State geologic map) and Karabinos (1984) and are now mapped as Hoosac Formation in this quad because of the presence of quartzite and dolomite locally contained within rusty albitic schist and granofels rocks typical of Hoosac. Similarly, cover rocks of Jamaica antiformal sheath fold consist of a 10-m-thick basal and quite continuous belt of dolomite marble that contains thin beds of vitreous quartzite. This unit was also mapped as Tyson by Doll and others (1961) and by Karabinos (1984) and is now mapped as Hoosac. Second revision is that Turkey Mountain Member is formalized as a member of Hoosac Formation to include all metabasalts within the formation. Exposed for a distance of 3 km northwest of Townshend. Consists of a collection of massive black amphibolite layers, 1 to 2 m thick, interlayered with epidotitic and quartz-rich, laminated greenstones. Total thickness of interbedded amphibolite and associated metasedimentary rock on Turkey Mountain is as much as 200 m. Termination of Turkey Mountain Member northward appears to result from thinning to the north although fault truncation along its lower contact cannot be ruled out. To the south, Turkey Mountain Member also appears to thin by interbedding with enclosing metasedimentary rocks, and pinches out north of Townshend. Where several layers in a limited region can be mapped separately, they are each referred to informally by use of subscripts in the letter symbol; this, however, does not imply correlation of numbered layers between different areas of the map (Ratcliffe, in press).
Littleton Formation (Devonian): Littleton Formation - Gray slate and phyllite containing interbeds of gray schistose quartzite 1/4 inch to 6 inches thick. West of Guildhall are lustrous, light to dark gray biotite-garnet phyllite and schist, some slate, and subordinate quartzite and impure quartzite. South of Bellows Falls gray phyllite passes eastward into gray mica schist containing porphyroblasts of biotite, garnet, and staurolite.
Missisquoi Formation (Ordovician): Missisquoi Formation - Rusty weathering carbonaceous mica schist, quartzite and micaceous quartzite.
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.
Northfield Formation (Devonian - Silurian): Northfield Formation - Dark gray to black quartz-sericite slate or phyllite with fairly widely-spaced interbeds a few inches thick of siltstone and silty crystalline limestone like that of the Waits River Formation; calcareous slate north of Lamoille River; phyllite passes into gray quartz-sericite schist containing abundant porphyroblasts of biotite and garnet in southern Vermont.
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.
Orfordville Formation, Sunday Mountain Volcanics (Ordovician): Orfordville Formation, Sunday Mountain Volcanics - Greenstone, chloritic schist, felsite, and quartz-feldspar-sericite schist.
Partridge Formation (Ordovician): Partridge Formation - Rusty weathering carbonaceous mica schist locally containing porphyroblasts of biotite, garnet, or staurolite. (Southeastern Vermont).
Pinney Hollow Formation (Cambrian): Pinney Hollow Formation - Pale green quartz-sericite (muscovite-paragonite)-chlorite phyllite and schist with abundant magnetite, chloritoid phyllite and schist, quartz-sericite-albite-chlorite schist, and rare beds of carbonaceous and schistose quartzite; garnet porphyroblasts common south of Ottauquechee River. (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 - Chiefly tan to brown weathered quartzose limestone and calcareous quartzite characterized by specks of limonite after ankerite; locally underlain by quartz conglomerate and overlain by blue fossiliferous crystalline limestone; greenstone and quartz-sericite schist.
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 (Cambrian-Ordovician): Stowe Formation - Quartz-sericite (muscovite-paragonite)-chlorite phyllite and schist; porphyroblasts of albite, garnet, chloritoid, or kyanite common locally; includes phyllitic graywacke north of Lamoille River. Schist contains abundant segregations of granular white quartz. The Stowe Formation in the study are contains two unnamed members: a silvery green schist and a greenstone. The schist is a fine-grained, silvery to dark green quartz-muscovite-albite-chlorite schist. It is in fault contact with the black phyllite of the Ottauquechee Formation. The greenstone is a homogenous, fine-grained, light green actinolite-albite-epidote-calcite-chlorite schist. Large outcrops of the resistant greenstone are common. Age according to map symbols is Proterozoic and Cambrian. Unit is correlated with the Rowe Schist (of Zen, 1983). [Rowe Schist on 1983 MA map is Cambrian and Ordovician. No explanation here for older age.] (Walsh, 1992).
Tyson Formation (Cambrian): Tyson Formation - Feldspathic quartz-mica schist containing biotite, chlorite, and carbonate; many beds contain pebbles of quartz and feldspar; cobble or boulder conglomerate commonly at base; thin beds of quartzite, carbonaceous phyllite, and schistose dolomite in upper part, overlain at top by massive buff dolomite as much as 30 ft thick. (Southern and Central Vermont). The Tyson Formation contains grits and conglomerates at its base that unconformably overlie basement. The conglomerates and grits are as much as 150 m thick and contain lenses of dolomitic quartzite and feldspathic grit. Unit also contains black carbonaceous phyllite and interbedded dolostone as much as 100 m thick, followed by beige to tan weathering beds of dolostone that increase in abundance toward the top of the unit and pass into punky weathering dolomitic and feldspathic quartzite at the top. From a point near the southwest corner of the Andover quad, the rocks of the Tyson Formation are laterally replaced by albitic schists and granofels of the Hoosac Formation to the south. Therefore, Tyson laterally replaces the Hoosac from south to north along the eastern margin of the Green Mountain massif. The Tyson Formation is of Late Proterozoic(?) and Early Cambrian age (Ratcliffe, 1994).
Underhill Formation (Cambrian): Underhill Formation - Silvery, gray-green, quartz-sericite-albite-chlorite-biotite schist, containing abundant lenticular segregations of granular white quartz; locally quartz-sercite-albite-chlorite phyllite; porphyroblasts of albite, garnet, and magnetite are common and locally very abundant in gneissic facies in axial anticlines of the Green Mountain anticlinorium . (Northern and Central Vermont). In study area consists mainly of greenish quartz-chlorite-sericite phyllites lying stratigraphically between Pinnacle and Cheshire Formations, where author would place rocks of type locality within Underhill facies of Pinnacle Formation, for they are clearly stratigraphically equivalent to rocks of Pinnacle Formation in Enosburg area, being below an excellent horizon marker, the Whitebrook dolomite and slate. However, Underhill facies of the Pinnacle and phyllites of Underhill Formation are practically indistinguishable in the field, and it is unavoidable, wherever dividing White Brook dolomite and slate are absent, to map all rocks of Underhill facies as one unit. In western part of outcrop belt, Underhill rocks are well defined between White Brook Dolomite or coarse Pinnacle graywacke below and Cheshire Formation above. Rocks in this clearly defined area are here recognized as Fairfield Pond Member. As mapped, the Underhill includes Fairfield Pond Member, Bakersfield Greenstone, Peaked Mountain Greenstone, White Brook Member, Jay Peak Member, and West Sutton Slate Member. Eastern facies of Underhill is named Bonsecours facies (Dennis, 1964).
Underhill Formation, Battell Member (Cambrian): Underhill Formation, Battell Member - Carbonaceous sericite-quartz-albite-chlorite schist and schistose quartzite, also carbonaceous and noncarbonaceous limestone; quartz-sericite-chlorite-albite schist. (Northern and Central Vermont). The Battell is raised to Formation rank by T.R. Armstrong (in press) [not in bibliography] to describe graphitic schists with carbonates that depositionally overlie the Monastery Formation in the Granville-Hancock area of central VT. The name Battell Formation is tentatively assigned in this report to a distinct group of graphitic rocks with limited occurrence in the study area. The basal portion of the Battell is assigned by Armstrong to the White River Member (new name) and following that nomenclature, the White River is the only part of the Battell seen in the Fayston-Buels Gore area. The White River appears to be in fault contact with the Underhill Formation along the eastern boundary of the Underhill in Buels Gore. The member also appears to be in depositional contact with the Monastery Formation at all observed locations and occurs as small bodies within the schists of the Monastery (Walsh, 1992).
Underhill Formation, carbonaceous quartz-sericite-albite-chlorite schist and phyllite. (Cambrian): Underhill Formation, carbonaceous quartz-sericite-albite-chlorite schist and phyllite. (Northern and Central Vermont).
Underhill Formation, Fairfield Pond Member (Cambrian): Underhill Formation, Fairfield Pond Member - Greenish quartzitic schist (quartz-sericite-albite-chlorite-biotite); sericite-quartz-chlorite phyllite, locally purple or red, common in lower part. (Northern and Central Vermont).
Underhill Formation, Foot Brook Member (Cambrian): Underhill Formation, Foot Brook Member - Sericite (muscovite-paragonite)-quartz-chlorite-chloritoid schist; minor carbonaceous interbeds. (Northern and Central Vermont).
Underhill Formation, Jay Peak Member (Cambrian): Underhill Formation, Jay Peak Member - Pale, silver-green, quartz-sericite-chlorite-albite schist, locally quartzitic. (Northern and Central Vermont).
Underhill Formation, Mount Abraham Schist Member (Cambrian): Underhill Formation, Mount Abraham Schist Member - Light gray sericite (muscovite-paragonite)-quartz-chloritoid rock with silvery sheen; porphyroblasts of magnetite are common and porphyroblasts of chlorite, chloritoid, garnet, and kyanite occur locally. (Northern and Central Vermont). Four distinctive units of Mount Abraham Schist occur within the Fayston-Buels Gore area, which are recognized on the basis of mineralogy, contact relationships, and geographic distribution. All are composed predominantly of white mica (muscovite and paragonite)-quartz-chlorite-chloritoid schist. One unit contains intraformational greenstone and metawacke; a second is a similar white mica schist but without the greenstone and metawacke; the third contains allanite; and the fourth, kyanite (Walsh, 1992).
Waits River Formation (Devonian): Waits River Formation - Gray quartzose and micaceous crystalline limestone weathered to distinctive brown earthy crust; interbedded and intergradational with gray quartz-muscovite phyllite or schist. Where more metamorphosed the limestones contain actinolite, hornblende, zoisite, diopside, wollastonite, and garnet, and the phyllite and schist, biotite, garnet, and locally andalusite, kyanite or sillimanite.

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