Geologic units in Connecticut (state in United States)

Mineral Resources On-Line Spatial Data

Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

Dalton Formation - Tan weathering, muscovite-microcline quartzite and feldspathic quartzite rich in black tourmaline, locally includes thin beds of other rock types listed below.

Lithology: quartzite

Waterford Group (Proterozoic Z?) at surface, covers 0.9 % of this area

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).

Lithology: gneiss; amphibolite

Pumpkin Ground Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician) at surface, covers 0.5 % of this area

Pumpkin Ground (porphyritic) Member [of Harrison (Prospect) Gneiss] - Medium- to light-gray, medium- to coarse-grained, well-layered and foliated gneiss, composed of oligoclase, microcline, quartz, and biotite; some layers have numerous microcline megacrysts 1 to 5 cm across; others have hornblende. Minor layers of garnetiferous schist and gneiss. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields ages of 428+/-2 Ma (Early Silurian) for the Pumpkin Ground and 446+/-2 Ma (Late Ordovician) for the Beardsley, accepted by authors as crystallization ages. Pumpkin Ground intrudes the Trap Falls Formation. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).

Lithology: gneiss; schist

Hope Valley Alaskite Gneiss (Proterozoic Z?) at surface, covers 2 % of this area

Hope Valley Alaskite Gneiss - Light-pink to gray, medium- to coarse-grained, locally porphyritic, variably lineated and foliated alaskitic gneiss, composed of microcline, quartz, albite or oligoclase, and minor magnetite, and locally biotite and muscovite. Lineation formed by rods of quartz. Locally contains quartz-sillimanite nodules.

Lithology: granitic gneiss

Collins Hill Formation (Upper? and Middle Ordovician) at surface, covers 0.8 % of this area

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.

Lithology: schist; gneiss; amphibolite; calc-silicate rock

New Haven Arkose (Upper Triassic; possibly Lower Jurassic at top) at surface, covers 6 % of this area

New Haven Arkose - Red, pink, and gray coarse-grained, locally conglomeratic, poorly sorted and indurated arkose, interbedded with brick-red micaceous, locally shaly siltstone and fine-grained feldspathic clayey sandstone.

Lithology: arkose; conglomerate; siltstone; sandstone

Portland Formation (Lower Jurassic) at surface, covers < 0.1 % of this area

Portland Formation - Reddish-brown to pale red conglomerate and arkose.

Lithology: conglomerate; arkose

Middle member [of Bigelow Brook Formation] (Silurian or perhaps Ordovician) at surface, covers < 0.1 % of this area

Middle member [of Bigelow Brook Formation] - Greenish-gray, medium-grained calc-silicate rock, composed of plagioclase, quartz, and diopside (locally hornblende and scapolite), interbedded with schist and granofels composed of plagioclase, quartz, biotite, and commonly garnet and sillimanite.

Lithology: calc-silicate rock; schist; granofels

Walloomsac Schist (Middle Ordovician) at surface, covers 0.6 % of this area

Walloomsac Schist - Black to dark-or silvery-gray, rarely layered schist or phyllite, composed of quartz, albite, and commonly garnet and staurolite or sillimanite (locally strongly retrograded to chlorite and muscovite). Locally feldspathic or calcareous near the base.

Lithology: schist; phyllite

Brimfield Schist (uncertain) (Upper? and Middle Ordovician) at surface, covers 0.1 % of this area

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.

Lithology: schist; gneiss; amphibolite; calc-silicate rock

Trap Falls Formation (Middle or Lower Ordovician) at surface, covers 0.3 % of this area

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.

Lithology: schist; gneiss; granulite; amphibolite

Tatnic Hill Formation (Upper? and Middle Ordovician) at surface, covers 3 % of this area

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.

Lithology: gneiss; schist; mica schist; amphibolite; calc-silicate rock

Litchfield Norite (Middle? Ordovician) at surface, covers < 0.1 % of this area

Litchfield Norite - Dark, medium- to coarse-grained, mostly massive mafic rock (olivine norite, quartz norite, hypersthene pyroxenite), composed of labradorite, hypersthene, augite, and olivine in varying proportions, also hornblende and biotite (and minor quartz in quartz norite). Associated with small mineral deposits of pyrrhotite, pentlandite, and chalcopyrite.

Lithology: norite; pyroxenite

Canterbury Gneiss (Devonian) at surface, covers 1 % of this area

Canterbury Gneiss (may be equivalent to Ayer Granite of Massachusetts) - Light-gray, medium-grained, variably foliated, locally strongly lineated gneiss, composed of quartz, oligoclase, microcline, and biotite, locally also muscovite, or epidote, and generally with megacrysts 1 to 2 cm long of either or both feldspars.

Lithology: gneiss

Hawley Formation (Middle Ordovician) at surface, covers 0.1 % of this area

Hawley Formation (carbonaceous schist facies) - Gray, rusty-weathering, fine- to medium-grained, generally layered schist and granofels, composed of quartz, oligoclase, and biotite; some muscovite and graphite, rare garnet and kyanite or sillimanite. Layers of quartz-spessartine rock (coticule) common.

Lithology: schist; granofels

Upper part [of Maltby Lakes Metavolcanics] (Middle? Ordovician) at surface, covers < 0.1 % of this area

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

Lithology: greenstone; greenschist; metavolcanic rock

Nonewaug Granite (Devonian) at surface, covers 0.6 % of this area

Nonewaug Granite - White to pink, fine- to very coarse-grained (commonly pegmatitic), massive to layered granite composed of albite, microcline, quartz, and muscovite, with minor biotite and garnet. Microcline commonly graphic; quartz and muscovite commonly in plumose aggregates.

Lithology: granite; pegmatite

Scranton Mountain Member [of Taine Mountain Formation] (Lower? Ordovician) at surface, covers < 0.1 % of this area

Scranton Mountain Member [of Taine Mountain Formation] - Gray, rusty-weathering, medium-grained schist, composed of quartz, muscovite, biotite, plagioclase, garnet, and generally kyanite. The Taine Mountain Formation of Stanley (1964) is here adopted in the Collinsville and Bristol quads, CT. Includes three pinstriped units, the Wildcat, Scranton Mountain, and Whigville Members of Stanley (1964), also adopted. Correlates with the Savoy Schist of Emerson (1898), Missisquoi Schist or Group of Richardson (1919, 1924), in MA; and the Moretown Formation of Cady (1956) in MA and VT. Age is Middle Ordovician (Simpson, 1990).

Lithology: schist

Cobble Mountain Formation (Middle Ordovician) at surface, covers 0.4 % of this area

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.

Lithology: schist; granofels; amphibolite

Buttress Dolerite (Middle? Jurassic) at surface, covers 0.2 % of this area

Buttress Dolerite - Dark-gray to greenish-gray (weathers brown or gray), medium- to fine-grained, commonly porphyritic, generally massive with well-developed columnar jointing, grading from basalt near contacts to fine-grained gabbro in the interior, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine.

Lithology: diabase; basalt; gabbro

Quartzite unit [in Scotland Schist] (Devonian or Silurian or both) at surface, covers < 0.1 % of this area

Quartzite unit [in Scotland Schist] - Quartzite, generally micaceous, interlayered with mica schist.

Lithology: quartzite; mica schist

Brimfield Schist (Upper? and Middle Ordovician) at surface, covers 3 % of this area

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.

Lithology: schist; gneiss; amphibolite; calc-silicate rock

Fitch Formation (Silurian) at surface, covers < 0.1 % of this area

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.

Lithology: calc-silicate rock; mica schist

Monson Gneiss (Middle or Lower Ordovician?) at surface, covers 3 % of this area

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.

Lithology: gneiss; amphibolite

Lower member [of Middletown Formation] (Middle Ordovician) at surface, covers 0.2 % of this area

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.

Lithology: amphibolite; mafic gneiss

Sweetheart Mountain Member [of Collinsville Formation] (Middle Ordovician) at surface, covers 0.1 % of this area

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).

Lithology: schist; amphibolite; metamorphic rock

Portland Arkose (Lower Jurassic) at surface, covers 8 % of this area

Portland Arkose - Reddish-brown to maroon micaceous arkose and siltstone and red to black fissile silty shale. Grades eastward into coarse conglomerate (fanglomerate).

Lithology: arkose; siltstone; shale; conglomerate

Glastonbury Gneiss (Ordovician) at surface, covers < 0.1 % of this area

Glastonbury Gneiss - Massive granitic gneiss in core of Glastonbury dome and in adjacent areas.

Lithology: granitic gneiss

Golden Hill Schist (Lower? Ordovician) at surface, covers 0.3 % of this area

Golden Hill Schist (may be equivalent to part of Trap Falls Formation) - Gray to silvery, medium- to coarse-grained, generally layered schist and granofels, composed of quartz, muscovite, biotite, plagioclase, and garnet.

Lithology: schist; granofels

Lebanon Gabbro (Devonian) at surface, covers 0.3 % of this area

Lebanon Gabbro - Dark, speckled, coarse-grained, massive but locally sheared gabbro, composed of hornblende, labradorite, and opaques. Some bodies contain biotite, and quartz; some smaller ones are nearly pure hornblende with local augite.

Lithology: gabbro

Silicified rock and mylonite along Mesozoic faults (probably mainly Jurassic) at surface, covers < 0.1 % of this area

Silicified rock and mylonite along Mesozoic faults - Close network of quartz veins and veinlets cutting each other and older rock, which is mostly replaced by very fine grained quartz. In places, incompletely replaced rock shows strongly mylonitic texture.

Lithology: mylonite

Unit a [of Stockbridge Marble] (Lower Cambrian) at surface, covers 0.2 % of this area

Unit a [of Stockbridge Marble] - White to pale-gray, massive, smooth-weathering dolomite marble.

Lithology: marble

East Berlin Formation (Lower Jurassic) at surface, covers 1 % of this area

East Berlin Formation - Maroon siltstone, silty and sandy shale, and fine-grained silty sandstone, generally well laminated and commonly well indurated, alternating with dark fissile shale; dolomitic carbonate common in cement, concretions, and thin argillaceous laminae. Local arkose; grades eastward into coarse conglomerate close to eastern border fault. The East Berlin Formation of the Hartford basin contains eight facies: trough cross-bedded sandstones, horizontally stratified sandstones, interbedded sandstones and mudrocks, ripple cross-laminated siltstones, black shales, stratified mudrocks, disrupted shales, and disrupted mudstones. These facies are interpreted as a continental depositional system and are divided into two assemblages. Sandflat/alluvial plain facies assemblage (sandstones and siltstones) is composed of sheet-flood deposits. The lacustrine assemblage (shales and mudrocks) represents a saline lake-playa system (Gierlowski-Kordesch and Rust, 1994).

Lithology: siltstone; shale; sandstone; dolostone (dolomite); arkose; conglomerate

Amphibolite unit [in Ratlum Mountain Schist] (Lower? Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: amphibolite; mafic gneiss

Whigville Member [of Taine Mountain Formation] (Lower? Ordovician) at surface, covers < 0.1 % of this area

Whigville Member [of Taine Mountain Formation] - Gray, medium-grained, generally fairly well layered to well-laminated ("pin-stripe") gneissic or schistose granofels, composed of quartz. oligoclase, biotite, muscovite, and garnet, and locally staurolite and kyanite or sillimanite. The Taine Mountain Formation of Stanley (1964) is here adopted in the Collinsville and Bristol quads., CT. Includes three pinstriped units, the Wildcat, Scranton Mountain, and Whigville Members of Stanley (1964), also adopted. Whigville Member consists of plagioclase-quartz gneiss marked by distinctive thin layering (pinstriping) of muscovite and biotite. Thickness is 3,000 ft. Overlies the Scranton Mountain Member; underlies the Bristol Gneiss (revised). The Taine Mountain correlates with the Savoy Schist of Emerson (1898), Missisquoi Schist or Group of Richardson (1919, 1924), in MA; and the Moretown Formation of Cady (1956) in MA and VT. Age is Middle Ordovician (Simpson, 1990).

Lithology: granofels

Plainfield Formation (Late Proterozoic? or older?) at surface, covers < 0.1 % of this area

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.

Lithology: quartzite; mica schist

The Straits Schist (Devonian or Silurian or both) at surface, covers 2 % of this area

The Straits Schist ( = Goshen Formation of Massachusetts) - Silvery to gray, non-rusty, coarse- to very coarse grained, generally poorly layered schist, composed of quartz, muscovite, biotite, oligoclase, garnet, and commonly with staurolite and kyanite or sillimanite; graphitic almost throughout. Distinctive sequence of metamorphic strata overlying the Collinsville Formation in the Bristol quad., is here correlated with the Straits Schist of Fritts (1963) in the Southington quad. Consists mainly of rusty-weathering, medium- to coarse-grained, commonly crenulated, garnet-bearing, graphitic, muscovite-rich, plagioclase-quartz schist with graded bedding. Unit is called The Straits Schist following the original usage of Rodgers and others (1959). In the southern part of the Bristol quad., unit includes the Southington Mountain Member (here reduced in rank) in its upper part. Age of The Straits is inferred to be Silurian or Devonian. Unit is tentatively correlated with the Goshen Formation based on lithologic similarities and a possible unconformity at the base (Simpson, 1990).

Lithology: schist

Gneiss (metavolcanic) member [of Brimfield Schist] (Upper? and Middle Ordovician) at surface, covers 0.4 % of this area

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.

Lithology: gneiss; schist; amphibolite; calc-silicate rock; metavolcanic rock

Hebron Gneiss (Silurian and Ordovician) at surface, covers 5 % of this area

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.

Lithology: schist; calc-silicate rock; mica schist

Yantic Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician) at surface, covers 0.8 % of this area

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.

Lithology: schist; mica schist

Allingtown Metavolcanics plus Maltby Lakes Metavolcanics (Middle? Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: greenstone; schist; greenschist; phyllite; amphibolite

Quinebaug Formation (Middle Ordovician or older) at surface, covers 2 % of this area

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.

Lithology: mafic gneiss

Sterling Igneous Suite - granite gneiss (Late Proterozoic) at surface, covers < 0.1 % of this area

Sterling Igneous Suite - granite gneiss - Pale pink to gray, medium-grained granite gneiss, commonly with small porphyroclasts of microcline/orthoclase. Similar to alaskite gneiss, but with more than 3% dark minerals. Composition is granite with generally less than 3% dark minerals. Compositions range from quartz monzonite to granite. Composed of sodic plagioclase, quartz, microcline, biotite, opaque minerals; minor muscovite common, garnet more rare; accessory apatite and zircon; sphene present in some rocks; secondary chlorite. Typically is compositionally homogeneous, with strong foliation and locally well-developed lineation defined by major minerals. Includes some rock mapped formerly as Ten Rod Granite Gneiss, Hope Valley Alaskite Gneiss, Potter Hill Granite Gneiss, and Scituate Granite Gneiss.

Lithology: granitic gneiss

Buttress Dolerite (uncertain) (Middle? Jurassic) at surface, covers < 0.1 % of this area

Buttress Dolerite (uncertain)- Dark-gray to greenish-gray (weathers brown or gray), medium- to fine-grained, commonly porphyritic, generally massive with well-developed columnar jointing, grading from basalt near contacts to fine-grained gabbro in the interior, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine.

Lithology: diabase; basalt; gabbro

Southington Mountain Member [of The Straits Schist] (Devonian or Silurian or both) at surface, covers 0.4 % of this area

Southington Mountain Member [of The Straits Schist] - Gray to silvery, non-rusty, medium-grained, well-layered alternating schist and granofels, composed of quartz, oligoclase, muscovite, biotite, and garnet, commonly with staurolite and kyanite (or sillimanite); schist commonly graphitic. Metamorphosed strata named Southington Mountain Schist by Fritts (1963) is traceable into southern Bristol quad., and is here revised as Southington Mountain Member of The Straits Schist. Consists of alternating bands of quartz-feldspar granulite and of graphitic, muscovite-biotite schist. Unit is characterized by distinct, widespread, graded bedding and locally abundant staurolite. Unit may correlate with the Goshen Formation of the Heath quad, MA-VT, of Middle Silurian to Early Devonian age (Simpson, 1990).

Lithology: schist; granofels

Metavolcanic member [of Collins Hill Formation] (Upper? and Middle Ordovician) at surface, covers 0.1 % of this area

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.

Lithology: amphibolite; schist; gneiss

Foliated quartz diorite (Devonian in part, probably Ordovician in part) at surface, covers < 0.1 % of this area

Foliated quartz diorite - Mainly dark-gray, medium-grained, well-foliated gneiss (locally strongly sheared, especially near contacts), composed of plagioclase, quartz, biotite, and hornblende, locally also pyroxene.

Lithology: mafic gneiss

Southbridge Formation (Silurian or Ordovician or both) at surface, covers 0.8 % of this area

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.

Lithology: granofels; schist; calc-silicate rock; amphibolite

Biotite granitic gneiss (Devonian) at surface, covers < 0.1 % of this area

Biotite granitic gneiss.

Lithology: granitic gneiss

Holyoke Basalt (Lower Jurassic) at surface, covers 1 % of this area

Holyoke Basalt - Greenish-gray to black (weathers bright orange to brown), fine- to coarse-grained, grading from basalt near contacts to gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass.

Lithology: basalt; gabbro

Scituate Granite Gneiss (Proterozoic Z?) at surface, covers 0.7 % of this area

Scituate Granite Gneiss - Light-pink to gray., medium- to coarse-grained, generally porphyritic, well-lineated and locally foliated granitic gneiss, composed of microcline, quartz, albite or orthoclase, biotite, hornblende, and magnetite. Megacrysts of microcline up to 3 cm long; lineation formed by splotches of biotite or by rods or quartz.

Lithology: granitic gneiss

Layered gneiss (Proterozoic Y) at surface, covers 2 % of this area

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.

Lithology: gneiss; calc-silicate rock; amphibolite

Rowe Schist plus Amphibolite unit [in Rowe Schist] (Lower Ordovician or Cambrian or both) at surface, covers < 0.1 % of this area

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.

Lithology: amphibolite; mafic gneiss

Littleton Formation (uncertain) (Devonian) at surface, covers < 0.1 % of this area

Littleton Formation (uncertain)- Gray to silvery, generally non-rusty, medium-grained, massive to well-layered alternating schist and micaceous quartzite, composed of quartz, muscovite, biotite, garnet, and oligoclase, also staurolite, graphite, and ilmenite, and in certain areas kyanite or sillimanite in schist.

Lithology: schist; quartzite

Rowe Schist (Lower Ordovician or Cambrian or both) at surface, covers 2 % of this area

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.

Lithology: schist; granofels; amphibolite; calc-silicate rock

Talcott Basalt (Lower Jurassic) at surface, covers 0.2 % of this area

Talcott Basalt - Greenish-gray to black (weathers bright orange to brown), fine- to medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass. Pillows in many places; volcanic breccia with fragmentary pillows in others.

Lithology: basalt; gabbro; volcanic breccia (agglomerate)

Well-layered hornblende-biotite gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Well-layered hornblende-biotite gneiss .

Lithology: mafic gneiss

Manhattan Formation, undivided (Ordovician?) at surface, covers < 0.1 % of this area

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.

Lithology: pelitic schist; gneiss; amphibolite

Shuttle Meadow Formation (Lower Jurassic) at surface, covers 0.5 % of this area

Shuttle Meadow Formation - Maroon to dark-gray, silty shale, siltstone, and fine-grained silty sandstone, generally well and thinly laminated. In the southern part of the State includes a layer, up to 5 m thick, of blue, commonly sandy, fine-grained limestone or dolomitic limestone, grading laterally into calcareous siltstone. Coarser and more arkosic to east and south, grading into conglomerate near the eastern border fault.

Lithology: shale; siltstone; sandstone; limestone. conglomerate

Ratlum Mountain Schist (Lower? Ordovician) at surface, covers 4 % of this area

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.

Lithology: schist; granofels; amphibolite; calc-silicate rock

Nodular member [of Harrison Gneiss] (Middle? Ordovician) at surface, covers < 0.1 % of this area

Nodular member [of Harrison Gneiss] - Harrison Gneiss containing prominent quartz-sillimanite nodules.

Lithology: gneiss

Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z) at surface, covers < 0.1 % of this area

Monson Gneiss - Layered to massive biotite-plagioclase gneiss, amphibolite, microcline augen gneiss.

Lithology: biotite gneiss; amphibolite; augen gneiss

Hornblende norite (Devonian?) at surface, covers < 0.1 % of this area

Hornblende norite - Dark, coarse-grained, massive rock, composed of bytownite, hornblende, and hypersthene.

Lithology: norite

Littleton Formation (Devonian) at surface, covers 0.4 % of this area

Littleton Formation - Gray to silvery, generally non-rusty, medium-grained, massive to well-layered alternating schist and micaceous quartzite, composed of quartz, muscovite, biotite, garnet, and oligoclase, also staurolite, graphite, and ilmenite, and in certain areas kyanite or sillimanite in schist.

Lithology: schist; quartzite

Glastonbury Gneiss (Middle? Ordovician) at surface, covers 2 % of this area

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.

Lithology: granitic gneiss; amphibolite

Potter Hill Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers < 0.1 % of this area

Potter Hill Granite Gneiss plus Narragansett Pier Granite - 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 (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.

Lithology: granitic gneiss; granite; pegmatite

Yonkers Gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Yonkers Gneiss - biotite and/or hornblende-quartz-feldspar gneiss.

Lithology: gneiss

Hoosac Schist (Cambrian?) at surface, covers 1 % of this area

Hoosac Schist - Light- to medium-gray, rusty-weathering, fine- to medium-grained schist and poorly layered schistose gneiss, composed of quartz, biotite, plagioclase, muscovite, and generally garnet and sillimanite or kyanite.

Lithology: schist; gneiss

Stockbridge Marble (Lower Ordovician and Cambrian) at surface, covers 0.9 % of this area

Stockbridge Marble (including Inwood Marble) - White to gray, massive to layered marble, generally dolomitic but containing calcite marble in upper part, locally interlayered with schist or phyllite and with calcareous siltstone or sandstone.

Lithology: marble; schist; phyllite; siltstone; sandstone

Harrison Gneiss (including Prospect Gneiss) (Middle? Ordovician) at surface, covers 0.8 % of this area

Harrison Gneiss (including Prospect Gneiss) - Interlayered dark- and light-gray, medium-grained, well-foliated gneiss, composed of andesine, quartz, hornblende, and biotite (also locally K-feldspar as megacrysts 1 to 5 cm long). Thought to be metavolcanic equivalent of unit Ob. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields ages of 428+/-2 Ma for the Pumpkin Ground and 446+/-2 Ma for the Beardsley. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).

Lithology: gneiss

Hornblende gneiss and amphibolite (Proterozoic Y) at surface, covers 0.8 % of this area

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.

Lithology: amphibolite; gneiss; felsic gneiss; calc-silicate rock; marble

Basal member [of The Straits Schist] (Silurian) at surface, covers < 0.1 % of this area

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.

Lithology: schist; amphibolite; marble; calc-silicate rock; quartzite

Beardsley Member [of Harrison (Prospect) Gneiss] (Middle? Ordovician) at surface, covers 0.5 % of this area

Beardsley (hornblendic) Member [of Harrison (Prospect) Gneiss] - Medium- to dark-gray, medium-grained, well-layered and lineated gneiss, composed of plagioclase, quartz, microcline, hornblende, biotite, and epidote. Microcline may occur as megacrysts 1 to 3 cm across. Minor layers of garnetiferous schist and rarely of calc-silicate rock or marble. Pumpkin Ground and Beardsley Members of Harrison Gneiss, formerly considered conformable metavolcanic members, are here recognized as juxtaposed metaplutonic units and are renamed the Beardsley and Pumpkin Ground orthogneisses. Isotopic dating yields crystallization ages of 428+/-2 Ma (Early Silurian) for the Pumpkin Ground and 446+/-2 Ma (Late Ordovician) for the Beardsley. Age of the Beardsley based on analysis of seven zircon and two sphene fractions. The Harrison Gneiss as described by Rodgers (1985) has no stratigraphic significance and cannot be correlated regionally (Sevigny and Hanson, 1993).

Lithology: gneiss; schist; calc-silicate rock; marble

Dioritic phase [of Lebanon Gabbro] (Devonian) at surface, covers < 0.1 % of this area

Dioritic phase [of Lebanon Gabbro] - White to black, streaked, medium-grained, foliated or sheared gneiss, composed of plagioclase, biotite, quartz, and generally hornblende.

Lithology: mafic gneiss

Amphibolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Amphibolite - commonly biotitic; garnetiferous, pyroxenic, in and adjacent to Adirondack Highlands.

Lithology: amphibolite

Middletown Formation (Middle Ordovician) at surface, covers 1 % of this area

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.

Lithology: gneiss; granofels; amphibolite; mafic gneiss; biotite gneiss; calc-silicate rock

Hampden Basalt (Lower Jurassic) at surface, covers 0.4 % of this area

Hampden Basalt - Greenish-gray to black (weathers bright orange to brown), fine- to medium-grained, grading from basalt near contacts to fine-grained gabbro in the interior, composed of pyroxene and plagioclase with accessory opaques and locally olivine or devitrified glass.

Lithology: basalt; gabbro

Erving Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Erving Formation - Granofels and schist where mapped separately.

Lithology: granulite; schist

Potter Hill Granite Gneiss (Proterozoic Z?) at surface, covers 1 % of this area

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. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. The Sterling, as defined here, includes only the Hope Valley Alaskite Gneiss and the Potter Hill Granite Gneiss. These rocks intrude the Plainfield Formation and the Waterford Group in southeastern CT and western Rhode Island and are Late Proterozoic in age. The gneiss of the Potter Hill is mainly weathered, deeply stained, somewhat crumbly, and generally slabby. Contains xenoliths of the Plainfield Formation. Is distinguished from Hope Valley by its higher biotite content (Skehan and Rast, 1990).

Lithology: granitic gneiss

Bristol Gneiss (Middle? Ordovician) at surface, covers 0.4 % of this area

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).

Lithology: gneiss; amphibolite

Scituate Granite Gneiss (Proterozoic Z) at surface, covers < 0.1 % of this area

Scituate Granite Gneiss - Gneissic granite containing biotite in small clots. Equivalent to part of former Northbridge Granite Gneiss (usage now abandoned). Gradational with Zhg.

Lithology: granite

Poughquag Quartzite (Cambrian) at surface, covers < 0.1 % of this area

Poughquag Quartzite - (includes local Dalton Formation at base)-locally conglomeratic.

Lithology: quartzite; conglomerate

Lamprophyre (Devonian?) at surface, covers < 0.1 % of this area

Lamprophyre - Dark-gray to greenish, fine-grained, badly altered dike rock, composed of biotite, augite, K-feldspar, and accessory apatite and sphene, plus secondary minerals.

Lithology: lamprophyre

Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Walloomsac Formation - slate, phyllite, schist, metagraywacke.

Lithology: slate; phyllite; schist; metasedimentary rock

Schist and granulite member [of Trap Falls Formation] (Middle or Lower Ordovician) at surface, covers 0.5 % of this area

Schist and granulite member [of Trap Falls Formation] - Interlayered gray to silvery, medium- to coarse-grained schist and fine-grained granofels, composed of quartz, sodic plagioclase, biotite, and muscovite; garnet common in schist.

Lithology: schist; granofels

Felsic gneiss member [of Quinebaug Formation] (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Felsic gneiss member [of Quinebaug Formation] - Light- to medium-gray, fine- to medium-grained gneiss, composed of plagioclase, quartz, biotite, and muscovite, commonly with K-feldspar.

Lithology: felsic gneiss

Narragansett Pier Granite (Permian) at surface, covers < 0.1 % of this area

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.

Lithology: granite; pegmatite

Plainfield Formation (Proterozoic Z?) at surface, covers 2 % of this area

Lithology: quartzite; mica schist; gneiss; amphibolite; calc-silicate rock

New Haven Arkose (Upper Triassic) at surface, covers < 0.1 % of this area

New Haven Arkose - Red, pink, and gray coarse-grained, locally conglomeratic arkose interbedded with brick-red shaley siltstone and fine-grained arkosic sandstone; boundary between Lower Jurassic (Jn) and Upper Triassic (TRn) parts is arbitrarily drawn through clastic rocks of similar lithology below gray mudstone containing Lower Jurassic palynofloral zone; TRn is continuous with and lithically similar to TRs near Northampton. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).

Lithology: arkose; siltstone; mudstone

Oronoque Schist (Lower? Ordovician) at surface, covers 0.4 % of this area

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.

Lithology: schist; granofels; amphibolite; greenstone

Clough Quartzite (Silurian) at surface, covers < 0.1 % of this area

Clough Quartzite - White, medium-grained, glassy to granular, well-layered quartzite and muscovitic quartzite, locally with garnet; conglomeratic (commonly with tourmaline) in lower part.

Lithology: quartzite; conglomerate

Porphyritic member [of Southbridge Formation] (Silurian or Ordovician or both) at surface, covers < 0.1 % of this area

Porphyritic member [of Southbridge Formation] - Light- to medium-gray, fine-grained porphyritic massive to layered gneiss, composed of quartz, oligoclase, microcline, and biotite, with megacrysts 1 to 2 cm long of microcline.

Lithology: gneiss

Joshua Rock Member [of New London Gneiss] (Proterozoic Z?) at surface, covers < 0.1 % of this area

Joshua Rock Member [of New London Gneiss] - Medium-gray (weathers with red spots of hematite), medium-grained, foliated gneiss composed of microperthite, quartz, albite, aegerine-augite, and magnetite; rare riebeckite.

Lithology: gneiss

Ponaganset Gneiss (Proterozoic Z?) at surface, covers 0.3 % of this area

Ponaganset Gneiss - Dark-gray, coarse-grained, porphyritic, well-foliated gneiss, composed of oligoclase, quartz, microcline (mostly as megacrysts up to 8 cm long), biotite, magnetite, and generally hornblende; also garnet and muscovite where hornblende is absent. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. Ponaganset lies east of the Hope Valley shear zone and extends from RI into MA. [Apparently does not occur in CT.] Predominantly granite, ranges to tonalite. Gray to light gray, some pink, generally medium- to coarse-grained, but ranges from fine-grained to porphyritic. Alkali K-feldspar, plagioclase, quartz, and biotite are major minerals. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. Strong lineation is defined by elongate aggregates of quartz and feldspar and trains of biotite and hornblende. Age is Late Proterozoic based on correlation with Northbridge Gneiss (MA), which has been dated at 557+/-4 Ma by Zartman and Naylor (1984) (Skehan and Rast, 1990).

Lithology: gneiss

Littleton Formation (Lower Devonian) at surface, covers < 0.1 % of this area

Littleton Formation - Black to gray aluminous mica schist, quartzose schist, and aluminous phyllite.

Lithology: schist; phyllite

Hornblende gneiss member [of Collinsville Formation] (Middle Ordovician) at surface, covers 0.4 % of this area

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.

Lithology: amphibolite; mafic gneiss; metamorphic rock

Waterford Group plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers 0.1 % of this area

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.

Lithology: gneiss; granitic gneiss; granite; pegmatite; amphibolite

Ordovician? granitic gneiss (Middle Ordovician?) at surface, covers < 0.1 % of this area

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.

Lithology: granitic gneiss

Collinsville Formation (Middle Ordovician) at surface, covers 1 % of this area

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

Lithology: gneiss; amphibolite; felsic metavolcanic rock; mafic metavolcanic rock; granulite

Dioritic phase [of Preston Gabbro] (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Dioritic phase [of Preston Gabbro] - Medium- to dark-gray, streaked or speckled, medium-grained diorite and quartz diorite, gneissic where sheared near contact, composed of plagioclase, hornblende, and biotite, and locally quartz and relic pyroxene.

Lithology: diorite; quartz diorite; gneiss

Ultramafic rock (Ordovician or older) at surface, covers < 0.1 % of this area

Ultramafic rock - Ultramafic rock, originally composed of olivine and pyroxene, now generally altered to tremolite, talc, chlorite, or serpentine.

Lithology: ultramafic intrusive rock; serpentinite

Allingtown Metavolcanics (Middle? Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: greenstone; phyllite

Upper member [of Bigelow Brook Formation] (Silurian and perhaps Ordovician) at surface, covers 0.4 % of this area

Upper member [of Bigelow Brook Formation] - Chiefly gray, rusty-weathering, medium-grained, generally well layered and locally fissile schist, composed of plagioclase, quartz, biotite, garnet, and sillimanite, locally with K-feldspar or cordierite, fissile layers commonly with graphite and pyrrhotite, interlayered with quartzose granofels with less biotite but with calc-silicate minerals.

Lithology: schist; granofels

Stockbridge Formation (Lower Ordovician) at surface, covers < 0.1 % of this area

Stockbridge Formation - White to blue-gray and white layered calcite marble.

Lithology: marble

Rusty mica schist and gneiss (Proterozoic Y; may contain some older rocks) at surface, covers 1 % of this area

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.

Lithology: schist; gneiss; quartzite; amphibolite

Fordham Gneiss (C and D member) (Precambrian - Middle Proterozoic ) at surface, covers < 0.1 % of this area

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.

Lithology: gneiss; amphibolite; quartzite

Cheshire Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area

Cheshire Quartzite - Mainly pure, white, glassy, tough quartzite.

Lithology: quartzite

Eastford gneiss phase [of Canterbury Gneiss] (Devonian) at surface, covers 0.6 % of this area

Eastford gneiss phase [of Canterbury Gneiss] - Mainly light-gray, medium-grained, foliated to strongly lineated gneiss, composed of quartz, microcline, oligoclase, or albite, biotite, and muscovite.

Lithology: gneiss

Lower member [of Bigelow Brook Formation] (Silurian or Ordovician or both) at surface, covers 0.7 % of this area

Lower member [of Bigelow Brook Formation] - Chiefly gray, medium-grained, well-layered granofels, composed of quartz, oligoclase, and biotite, commonly with garnet and sillimanite, interlayered with thinly fissile sillimanitic, graphitic, pyrrhotite schist.

Lithology: granofels; schist

Light House Gneiss (Proterozoic Z?) at surface, covers < 0.1 % of this area

Light House Gneiss - Light-pink or gray to red, medium-grained, generally well foliated granitic gneiss, composed of K-feldspar, oligoclase, quartz, biotite, and magnetite, with local muscovite but no garnet.

Lithology: granitic gneiss

Stockbridge Formation (Cambrian - Lower Ordovician) at surface, covers < 0.1 % of this area

Stockbridge Formation - calcitic and dolomitic marble.

Lithology: marble

Taine Mountain and Collinsville Formations undivided (Middle to Lower? Ordovician) at surface, covers 0.3 % of this area

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

Lithology: gneiss; amphibolite;; granofels; felsic metavolcanic rock; mafic metavolcanic rock

Taine Mountain Member (Lower? Ordovician) at surface, covers 0.9 % of this area

Taine Mountain Member - Gray, medium-grained, generally fairly well layered to well-laminated ("pin-stripe") gneissic or schistose granofels, composed of quartz, oligoclase, biotite, muscovite, and garnet, and locally staurolite and kyanite or sillimanite. The Taine Mountain Formation of Stanley (1964) is here adopted in the Collinsville and Bristol quads, CT. Includes 3 pinstriped units: the Wildcat, Scranton Mountain, and Whigville Members, also adopted from Stanley (1964). Underlies Bristol Gneiss (revised). Correlates with the Savoy Schist of Emerson (1898), Missisquoi Schist or Group of Richardson (1919, 1924), in MA; and the Moretown Formation of Cady (1956) in MA and VT. Age is Middle Ordovician (Simpson, 1990).

Lithology: granofels

Ordovician? granitic gneiss (Middle Ordovician?) at surface, covers 2 % of this area

Lithology: granitic gneiss; schist

Tatnic Hill Formation (Ordovician or Proterozoic Z) at surface, covers < 0.1 % of this area

Tatnic Hill Formation - Sulfidic sillimanite schist, sillimanite schist and gneiss, biotite gneiss; minor amphibolite, calc-silicate gneiss and marble.

Lithology: schist; gneiss; biotite gneiss; amphibolite; marble

Paxton Formation (Silurian) at surface, covers < 0.1 % of this area

Paxton Formation - Undifferentiated biotite granofels, calc-silicate granofels, and sulfidic schist. 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).

Lithology: granofels; schist

Fordham Gneiss, undivided (Precambrian - Middle Proterozoic ) at surface, covers < 0.1 % of this area

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.

Lithology: gneiss; amphibolite; granulite; quartzite

Wepawaug Schist (Devonian or Silurian or both) at surface, covers 0.8 % of this area

Wepawaug Schist - Medium- to dark-gray, medium- to fine-grained, well-layered schist or phyllite and metasiltstone, composed of quartz, muscovite or sericite, plagioclase, biotite, and in appropriate metamorphic zones chlorite, garnet, staurolite, and kyanite. Schist or phyllite generally graphic.

Lithology: schist; phyllite; metasedimentary rock

Carringtons Pond Member [of Trap Falls Formation] (Middle or Lower Ordovician) at surface, covers 0.5 % of this area

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.

Lithology: schist; gneiss; amphibolite

Biotite-hornblende diorite and quartz-bearing diorite (Devonian) at surface, covers < 0.1 % of this area

Biotite-hornblende diorite and quartz-bearing diorite - Mostly foliated; intrudes Dl.

Lithology: diorite; quartz diorite

Plainfield Formation plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers < 0.1 % of this area

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.

Lithology: quartzite; mica schist; gneiss; granitic gneiss; granite; amphibolite; calc-silicate rock; pegmatite

Harrison Gneiss (Middle? Ordovician) at surface, covers < 0.1 % of this area

Lithology: gneiss

Washington Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Washington Gneiss - Well-layered, rusty-tan weathering muscovite-biotite plagioclase-microcline-quartz granofels containing layers of rusty sulfidic calc-silicate rocks.

Lithology: granofels; calc-silicate rock

Quartzite unit [in Plainfield Formation] (Proterozoic Z?) at surface, covers 0.6 % of this area

Quartzite unit [in Plainfield Formation] - Light-gray, glassy, generally thin bedded quartzite, also feldspathic and micaceous quartzite containing quartz-sillimanite nodules.

Lithology: quartzite

New London Gneiss (Proterozoic Z?) at surface, covers 0.4 % of this area

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).

Lithology: granitic gneiss; amphibolite

Basal member of upper slice of Canaan Mountain Schist (Cambrian?) at surface, covers < 0.1 % of this area

Basal member of upper slice of Canaan Mountain Schist - Gray, generally rusty- or tan-weathering gneiss, composed of quartz, plagioclase, microcline, biotite, and muscovite, interlayered with feldspathic quartzite.

Lithology: gneiss; quartzite

Washington Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Washington Gneiss - Coarse- to medium-grained hornblende-garnet amphibolite, hornblende-plagioclase gneiss and phlogopite-hornblende-plagioclase amphibolite (metabasalt).

Lithology: amphibolite; mafic gneiss; meta-basalt

Basal member [of Taine Mountain Formation] (Lower? Ordovician) at surface, covers 0.4 % of this area

Basal member [of Taine Mountain Formation] around Waterbury dome - Differs from rest of Taine Mountain Formation in being especially well layered and generally less micaceous and schistose.

Lithology: granofels

Rope Ferry Gneiss (Proterozoic Z?) at surface, covers 1 % of this area

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).

Lithology: gneiss; amphibolite

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Stockbridge Formation - White to light-powdery-blue-gray dolostone with disseminated grains of quartz and prominent sprays of tremolite in higher-grade areas.

Lithology: dolostone (dolomite)

Mamacoke Formation (Proterozoic Z?) at surface, covers 0.7 % of this area

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.

Lithology: gneiss; quartzite; amphibolite; calc-silicate rock

Preston Gabbro (Middle Ordovician or older) at surface, covers 0.2 % of this area

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.

Lithology: gabbro

Sterling Igneous Suite - alaskite gneiss (Late Proterozoic) at surface, covers < 0.1 % of this area

Sterling Igneous Suite - alaskite gneiss - Pale pink, orange, or gray, fine- to medium-grained granite gneiss, rarely with porphyroclasts of microcline/orthoclase. Composition is granite with generally less than 3% dark minerals. Composed of sodic plagioclase, quartz, microcline/orthoclase, minor biotite, and opaque minerals; minor muscovite (in part secondary), and rare garnet and sphene in some rocks; accessory apatite and zircon; secondary chlorite. Varies from massive to layered. Strongly foliated and locally well lineated. Includes most rock mapped formerly as Hope Valley Alaskite Gneiss.

Lithology: granitic gneiss

Dalton Formation (Lower Cambrian and Proterozoic Z) at surface, covers < 0.1 % of this area

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.

Lithology: mica schist; quartzite; conglomerate; schist

Quartzite unit [in Plainfield Formation] plus Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers < 0.1 % of this area

Quartzite unit [in Plainfield Formation] plus Stony Creek Granite Gneiss plus Narragansett Pier Granite - Quartzite unit [in Plainfield Formation] - light-gray, glassy, generally thin bedded quartzite, also feldspathic and micaceous quartzite containing 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.

Lithology: quartzite; granitic gneiss; granite; pegmatite

Mylonite along Paleozoic faults (Upper or Middle Paleozoic) at surface, covers 0.1 % of this area

Mylonite along Paleozoic faults - Mylonite, blastomylonite, and blastomylonitic gneiss, composed of intensely granulated quartz, plagioclase, biotite, and epidote, in places with hornblende or microcline and commonly with secondary minerals. In places has later been silicified (compare unit Jsi)..

Lithology: mylonite; gneiss

Tyringham Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Tyringham Gneiss - Light pinkish-gray ferrohastingsite-biotite, quartz-rodded granodioritic to quartz monzonitic gneiss, coarsely porphyritic, locally having fine-grained aplitic border. Intrudes all Berkshire Proterozoic Y units.

Lithology: granitic gneiss

Maltby Lakes Metavolcanics (Middle? Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: greenstone; greenschist; schist; amphibolite

Fly Pond (calc-silicate) Member [of Tatnic Hill Formation] (Upper? and Middle Ordovician) at surface, covers 0.5 % of this area

Fly Pond (calc-silicate) Member [of Tatnic Hill Formation] - Light-gray, medium-grained, layered to massive calc-silicate gneiss, composed of andesine, quartz, hornblende or actinolite, epidote, and commonly diopside, biotite, and scapolite; some layers are calcitic.

Lithology: gneiss

Biotite granite gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Biotite granite gneiss - overprint signifies inequigranular texture.

Lithology: granitic gneiss

Waterbury Gneiss (Proterozoic Z or Cambrian or both) at surface, covers 0.9 % of this area

Waterbury Gneiss - Medium- to dark-gray, fine- to medium-grained, generally irregularly foliated and lenticular rather than regularly layered schist and schistose gneiss, composed of biotite, quartz, oligoclase, kyanite (or sillimanite), and garnet, also locally microcline, irregularly mixed with granitoid gneiss, composed of oligoclase or andesine, quartz, biotite, and commonly microcline and muscovite.

Lithology: schist; gneiss

Scotland Schist (Devonian or Silurian or both) at surface, covers 1 % of this area

Scotland Schist - Gray to silvery, locally rusty, fine- to medium-grained schist, composed of quartz, muscovite, biotite, staurolite, and oligoclase, locally with kyanite or sillimanite; interlayered, especially below and to the west, with quartz-oligoclase-biotite schist and granofels and locally with quartzite.

Lithology: schist; granofels; quartzite

Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Walloomsac Formation - Dark-gray, graphitic quartz phyllite and schist containing minor lenses of limestone.

Lithology: phyllite; schist; limestone

Brookfield Gneiss (Middle? Ordovician) at surface, covers 1 % of this area

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.

Lithology: orthogneiss; amphibolite; mica schist

Golden Hill Schist (Lower? Ordovician) at surface, covers < 0.1 % of this area

Lithology: schist; granofels

Lower slice of Canaan Mountain Schist (Cambrian?) at surface, covers 0.1 % of this area

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.

Lithology: schist; amphibolite

Plainfield Formation plus Potter Hill Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers 0.3 % of this area

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.

Lithology: quartzite; mica schist; gneiss; granitic gneiss; granite; amphibolite; calc-silicate rock; pegmatite

Pink granitic gneiss (Proterozoic Y) at surface, covers 1 % of this area

Pink granitic gneiss - Light-pink to gray, medium- to coarse-grained, foliated but generally massive or poorly layered granitic gneiss, composed of quartz, microcline, oligoclase, and either biotite or muscovite or both, also locally amphibole or epidote.

Lithology: granitic gneiss

White to gray and black-spotted muscovite-biotite granite and granodiorite (Ordovician) at surface, covers < 0.1 % of this area

White to gray and black-spotted muscovite-biotite granite and granodiorite - Intruded near or along thrust faults. Intrudes CAZh and Proterozoic Y gneisses.

Lithology: granite; granodiorite

Stony Creek Granite Gneiss plus Narragansett Pier Granite (Proterozoic Z? and Permian) at surface, covers < 0.1 % of this area

Stony Creek Granite Gneiss plus Narragansett Pier Granite - 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.

Lithology: granitic gneiss; granite; pegmatite

Washington Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

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

Lithology: mica schist; conglomerate; felsic metavolcanic rock

Harrison/Ravenswood Gneiss (Ordovician?) at surface, covers < 0.1 % of this area

Harrison Gneiss - in New York and Connecticut, Brookfield diorite gneiss in Connecticut, and Ravenswood Gneiss in Brooklyn - biotite-hornblende-quartz- plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.

Lithology: gneiss; augen gneiss

Everett Schist (Cambrian?) at surface, covers 0.2 % of this area

Everett Schist - Grayish to greenish (some rusty-weathering), fine- to medium-grained, foliated but poorly layered schist or phyllite, composed of quartz, albite or oligoclase, muscovite, garnet, staurolite or chloritoid, and generally chlorite. Local layers are dark-gray to silvery schist or phyllite.

Lithology: schist; phyllite

Granitoid Gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Granitoid gneiss - Biotite ferrohastingsite granodioritic and granitic gneiss with large schlieren of biotite, locally contains garnet and muscovite.

Lithology: granitic gneiss

Preston Gabbro plus Quinebaug Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

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.

Lithology: gabbro; gneiss; amphibolite

Erving Formation (Devonian) at surface, covers < 0.1 % of this area

Erving Formation - Gray, medium-grained, well-foliated and generally well layered granofels and schist, composed of quartz, plagioclase, and biotite, also muscovite in schist, and accessory garnet and kyanite.

Lithology: granofels; schist

Maromas Granite Gneiss (Devonian?) at surface, covers < 0.1 % of this area

Maromas Granite Gneiss - Light-gray to buff, medium- to fine-grained granitic gneiss, composed of quartz and microcline with minor plagioclase and biotite. Central body is massive, but outlying strips are foliated and have accessory hornblende or garnet. Massive parts may be young anatectic intrusive rocks; foliated parts may include older felsic metavolcanic rocks belonging to unit Ochv. Pegmatite bodies are common in the vicinity.

Lithology: granitic gneiss; felsic metavolcanic rock; pegmatite

Cheshire Quartzite (Lower Cambrian) at surface, covers < 0.1 % of this area

Cheshire Quartzite - White, massive vitreous quartzite.

Lithology: quartzite

Bedford Gneiss (Ordovician?) at surface, covers < 0.1 % of this area

Bedford Gneiss - biotite-quartz-plagioclase gneiss and interlayered amphibolite; in part with augen of andesine and microcline.

Lithology: gneiss; amphibolite; augen gneiss

Unit c [of Stockbridge Marble] (Upper Cambrian) at surface, covers 0.6 % of this area

Unit c [of Stockbridge Marble] - Gray, generally massive dolomite marble, commonly contains quartz grains, locally beds of sandstone; may be calcitic near top.

Lithology: marble; sandstone

Mafic phase [of Narragansett Pier Granite] (Permian) at surface, covers < 0.1 % of this area

Mafic phase [of Narragansett Pier Granite] - Gray to reddish, medium-grained, generally massive granite, like Pn but with more biotite and locally hornblende.

Lithology: granite

Foliated granitic gneiss (Devonian?) at surface, covers < 0.1 % of this area

Foliated granitic gneiss - Light-gray, coarse-grained, strongly to weakly foliated gneiss, composed of phenocrysts of K-feldspar in a groundmass of plagioclase, quartz, K-feldspar, and biotite, with accessory sillimanite and garnet.

Lithology: granitic gneiss

Units e and d [of Stockbridge Marble] (Lower Ordovician) at surface, covers 0.1 % of this area

Units e and d [of Stockbridge Marble] - White to gray massive calcite marble, commonly mottled with dolomite and locally interlayered with dolomite marble and calcareous siltstone and sandstone.

Lithology: marble; dolostone (dolomite); siltstone; sandstone

Pinewood Adamellite (Permian) at surface, covers < 0.1 % of this area

Pinewood Adamellite - Light-gray, medium-grained, massive adamellite, composed of microcline, albite, quartz, and muscovite with accessory fluorite. High radioactivity.

Lithology: quartz monzonite

Portland Formation (Lower Jurassic) at surface, covers < 0.1 % of this area

Portland Formation - Reddish-brown to pale red arkose and siltstone, and gray sandstone, gray siltstone, and black shale interpreted as lake beds.

Lithology: arkose; siltstone; sandstone; black shale

Massive mafic rock (in Middletown Formation) (Middle Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: amphibolite

Tatnic Hill Formation (Ordovician or Proterozoic Z) at surface, covers < 0.1 % of this area

Tatnic Hill Formation - Yantic Member - Gray mica schist.

Lithology: mica schist

Lower part [of Maltby Lakes Metavolcanics] (Middle? Ordovician) at surface, covers < 0.1 % of this area

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

Lithology: greenschist; greenstone; schist; phyllite; metavolcanic rock; metasedimentary rock

Manhattan Schist (Cambrian?) at surface, covers 2 % of this area

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).

Lithology: gneiss; amphibolite

Partridge Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Mafic and felsic gneisses of volcanic derivation with calc-silicate granofels.

Lithology: mafic gneiss; felsic gneiss; granofels

Inwood Marble (Early Cambrian - Lower Ordovician) at surface, covers < 0.1 % of this area

Inwood Marble - dolomite marble, calc-schist, granulite, and quartzite, overlain by calcite marble; grades into underlying patchy Lowerre Quartzite of Early Cambrian age.

Lithology: marble; schist; granulite; quartzite

West Rock Dolerite (Lower Jurassic) at surface, covers 0.1 % of this area

West Rock Dolerite - Dark-gray to greenish-gray (weathers bright orange to brown), medium- to fine-grained, grading from basalt near contacts to fine-grained gabbro in the interior, generally massive with well-developed columnar jointing, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine.

Lithology: diabase; basalt; gabbro

Holyoke Basalt (Lower Jurassic) at surface, covers < 0.1 % of this area

Holyoke Basalt - Thick, columnar quartz tholeiite containing local gabbroic segregations, thinks eastward; interpreted as one or more thick ponded lava flows. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).

Lithology: tholeiite; gabbro

Upper member [of Middletown Formation] (Middle Ordovician) at surface, covers 0.2 % of this area

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.

Lithology: gneiss; granofels; amphibolite; biotite gneiss

Rowe Schist (Lower Ordovician or Cambrian or both) at surface, covers < 0.1 % of this area

Lithology: schist

Middletown Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Lithology: gneiss; granofels; mafic gneiss; amphibolite; calc-silicate rock

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.

Lithology: metasedimentary rock; gneiss

Ayer Granite (Lower Silurian) at surface, covers < 0.1 % of this area

Ayer Granite - Granite to tonalite, partly porphyritic; locally gneissic, locally muscovitic; may include rocks older than Silurian; intrudes Sb and So. Ayer Granite is divided into the Clinton facies and the Devens-Long Pond facies (Gore, 1976). In addition, there are some masses not assigned to either facies that intrude Berwick Formation west and northwest of Lawrence, and that intrude Paxton and Oakdale Formations south of Worcester and west of probable southern continuation of Wekepeke fault. Radiometric ages obtained for facies of Ayer pose problems in assigning ages to unfossiliferous sedimentary rocks they intrude. Clinton facies has a well-defined U-Pb zircon age of 433 +/-5 Ma (Zartman and Naylor, 1984) that authors cite as Early Silurian; Devens-Long Pond facies has a similar age. This age greatly compresses the time available for deposition, burial, deformation, and metamorphism of Berwick and Paxton if these units are truly Silurian. Some of the Ayer not assigned to a facies may have been more properly correlated with Early Devonian Chelmsford Granite and muscovite-biotite granite at Millstone Hill. Bodies south of Worcester may be more properly correlated with Canterbury Gneiss of CT, which lies on strike with Ayer and has Early Devonian age of 329 +/-9 Ma (Zartman and Naylor, 1984). Zartman and Naylor (1984) believe Ayer Granite has same age range as Newburyport Complex. It is quite possible, based on textural and mineralogical differences that the two facies should be separate units, representing different magmatic events (Wones and Goldsmith, 1991).

Lithology: granite; tonalite

Walloomsac Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Walloomsac Formation - Orange-brown weathering, graphite-albite-biotite calcitic marble and schistose marble and interbedded black phyllite.

Lithology: marble; phyllite

Upper slice of Canaan Mountain Schist (Cambrian?) at surface, covers 0.4 % of this area

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.

Lithology: schist; gneiss; amphibolite

Waterford Group and Branford Gneiss (Proterozoic Z?) at surface, covers 0.1 % of this area

Lithology: gneiss; granitic gneiss; amphibolite

Esmond Igneous Suite - granite gneiss (Late Proterozoic) at surface, covers < 0.1 % of this area

Esmond Igneous Suite - granite gneiss - Pale-gray to pale-pink, fine- to medium-grained granite gneiss, rarely with porphyroclasts of microcline/orthoclase. Composition ranges from quartz monzonite to granite. Composed of sodic plagioclase, quartz, microcline, biotite, opaque minerals; minor muscovite common, garnet more rare; accessory apatite and zircon; sphene and hornblende present in some rocks; secondary chlorite. Typically massive, but with strong penetrative foliation and lineation defined by major minerals. Commonly associated with, and in part gradational into, augen gneiss. Includes rock mapped formerly in part as Ponaganset Granite Gneiss, Scituate Granite Gneiss, Ten Rod Granite Gneiss, and Hope Valley Alaskite Gneiss.

Lithology: granitic gneiss; augen gneiss

Everett Schist (Cambrian?) at surface, covers < 0.1 % of this area

Everett Schist - minor meta-graywacke lenses. Includes Greylock Schist in Massachusetts.

Lithology: schist; metasedimentary rock

West Rock Dolerite (uncertain) (Lower Jurassic) at surface, covers < 0.1 % of this area

West Rock Dolerite (uncertain) - Dark-gray to greenish-gray (weathers bright orange to brown), medium- to fine-grained, grading from basalt near contacts to fine-grained gabbro in the interior, generally massive with well-developed columnar jointing, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine.

Lithology: basalt; gabbro

Southbridge Formation (Silurian or Ordovician or both) at surface, covers 0.3 % of this area

Lithology: granofels; schist

Porphyry (dacite or rhyolite) (Permian) at surface, covers < 0.1 % of this area

Porphyry (dacite or rhyolite) - Light-colored, very fine grained, massive porphyry with phenocrysts of quartz, feldspar, and biotite; muscovite and accessory fluorite in groundmass.

Lithology: rhyolite; dacite

Shelton Member [of Trap Falls Formation] (Middle or Lower Ordovician) at surface, covers 0.3 % of this area

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).

Lithology: granitic gneiss; biotite gneiss; mica schist; calc-silicate rock

Rusty and gray biotite-quartz-feldspar gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Rusty and gray biotite-quartz-feldspar gneiss - rusty facies contains variable amounts of garnet, sillimanite, cordierite, graphite, sulfides; minor marble and calcsilicate rock.

Lithology: gneiss; marble; calc-silicate rock

Mount Pisgah Member of Littleton Formation (Devonian) at surface, covers < 0.1 % of this area

Mount Pisgah Member of Littleton Formation - Gray, medium-grained, well-layered (locally graded) granofels or micaceous quartzite with some schist, composed of quartz, oligoclase, biotite, garnet, and sillimanite.

Lithology: granofels; quartzite; schist

Units g and f [of Stockbridge Marble] (Lower Ordovician) at surface, covers < 0.1 % of this area

Units g and f [of Stockbridge Marble] - White to gray massive calcite marble with layers and laminae of dolomitic marble.

Lithology: marble

Porphyritic phase [of Potter Hill Granite Gneiss] (Proterozoic Z?) at surface, covers 0.2 % of this area

Porphyritic phase [of Potter Hill Granite Gneiss] - Light- to medium-gray, fine- to medium-grained, porphyritic, well-foliated (not lineated) granitic gneiss, composed of microcline (much of it as megacrysts up to 4 cm long), quartz, oligoclase, biotite and magnetite. Sterling Plutonic Suite is here restricted to the Hope Valley terrane. (The Hope Valley together with the Esmond-Dedham terrane make up the Avalon superterrane of this report.) The Ponaganset Gneiss and the Ten Rod Granite Gneiss lie within the Esmond-Dedham terrane and are therefore removed from the Sterling. The Ponaganset is interpreted as an intensely deformed phase of the Esmond Plutonic Suite. The Sterling, as defined here, includes only the Hope Valley Alaskite Gneiss and the Potter Hill Granite Gneiss. These rocks intrude the Plainfield Formation and the Waterford Group in southeastern CT and western Rhode Island and are Late Proterozoic in age. The gneiss of the Potter Hill is mainly weathered, deeply stained, somewhat crumbly, and generally slabby. Contains xenoliths of the Plainfield Formation. Is distinguished from Hope Valley by its higher biotite content (Skehan and Rast, 1990).

Lithology: granitic gneiss

Ammonoosuc Volcanics (Middle Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: amphibolite; felsic gneiss; quartzite; marble

Ratlum Mountain Schist (Lower Ordovician) at surface, covers 0.3 % of this area

Lithology: schist; granofels; amphibolite; calc-silicate rock

Unit b [of Stockbridge Marble] (Upper and Middle? Cambrian) at surface, covers 0.4 % of this area

Unit b [of Stockbridge Marble] - White, pink, cream, and light-gray, generally well bedded dolomitic marble interlayered with phyllite and schist and with siltstone, sandstone, or quartzite, commonly dolomitic.

Lithology: marble; phyllite; schist; siltstone; sandstone; quartzite

Gneiss of Highlands massifs (Proterozoic Y; may contain some older rocks) at surface, covers 0.7 % of this area

Gneiss of Highlands massifs, (including Fordham Gneiss) - Mixture of rock types described below, where not separately mapped.

Lithology: gneiss; amphibolite; schist

Wildcat Member [of Taine Mountain Formation] (Lower? Ordovician) at surface, covers < 0.1 % of this area

Wildcat Member [of Taine Mountain Formation] - Gray, medium-grained, generally fairly well layered to well-laminated ("pin-stripe") gneissic or schistose granofels, composed of quartz, oligoclase, biotite, muscovite, and garnet, and locally staurolite and kyanite or sillimanite. The Taine Mountain Formation of Stanley (1964) is here adopted in the Collinsville and Bristol quads., CT. Includes three pinstriped units, the Wildcat, Scranton Mountain, and Whigville Members of Stanley (1964), also adopted. Wildcat Member is the basal pinstriped gneiss unit of the Taine Mountain, which correlates with the Savoy Schist of Emerson (1898), Missisquoi Schist or Group of Richardson (1919, 1924) in MA; and the Moretown Formation of Cady (1956) in MA and VT. Inferred age is Middle Ordovician (Simpson, 1990).

Lithology: granofels

Ratlum Mountain Schist plus Amphibolite unit [in Ratlum Mountain Schist] (Lower Ordovician) at surface, covers < 0.1 % of this area

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.

Lithology: schist; granofels; amphibolite; mafic gneiss; calc-silicate rock

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers < 0.1 % of this area

Gray, well-layered biotite-plagioclase-quartz gneiss - Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.

Lithology: granitic gneiss; amphibolite; schist; quartzite; gneiss

Hartland Formation (Ordovician?) at surface, covers < 0.1 % of this area

Hartland Formation - basal amphibolite overlain by pelitic schists.

Lithology: amphibolite; pelitic schist

Black Hill Member [of Quinebaug Formation] (Middle Ordovician or older) at surface, covers 0.2 % of this area

Black Hill Member [of Quinebaug Formation] - Gray, medium- to fine-grained, well-layered schist and granofels, composed of oligoclase, quartz, and biotite, commonly with hornblende or muscovite, and locally with calcite, garnet, or epidote.

Lithology: schist; granofels

New Haven Arkose plus Buttress Dolerite (Upper Triassic; possibly Lower Jurassic at top plus Middle? Jurassic) at surface, covers < 0.1 % of this area

New Haven Arkose plus Buttress Dolerite - New Haven Arkose - Red, pink, and gray coarse-grained, locally conglomeratic, poorly sorted and indurated arkose, interbedded with brick-red micaceous, locally shaly siltstone and fine-grained feldspathic clayey sandstone. Buttress Dolerite (Middle? Jurassic) - Dark-gray to greenish-gray (weathers brown or gray), medium- to fine-grained, commonly porphyritic, generally massive with well-developed columnar jointing, grading from basalt near contacts to fine-grained gabbro in the interior, composed of plagioclase and pyroxene with accessory opaques and locally devitrified glass, quartz, or olivine.

Lithology: arkose; diabase; conglomerate; siltstone; sandstone

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Stockbridge Formation - Beige, tan, and dark-gray weathering quartzose dolomite marble containing interbeds of black, green and maroon phyllite and punky weathering blue quartz pebble quartzite.

Lithology: marble; phyllite; quartzite

Amphibolite-bearing unit of Manhattan Schist (Cambrian?) at surface, covers 0.5 % of this area

Amphibolite-bearing unit of Manhattan Schist - Like Manhattan Schist but with numerous lenses and layers of amphibolite.

Lithology: gneiss; amphibolite

Stockbridge Formation (Lower Cambrian) at surface, covers < 0.1 % of this area

Stockbridge Formation - Massive to finely laminated steel-gray calcitic dolomite marble containing a prominent zone of white quartz nodules near top.

Lithology: marble

Syenite (Permian) at surface, covers < 0.1 % of this area

Syenite - Medium-gray, massive syenite, composed of microcline, amphibole (arfvedsonite), and biotite with accessory apatite and sphene.

Lithology: syenite

Dalton Formation (Lower Cambrian and perhaps partly older) at surface, covers 0.8 % of this area

Dalton Formation (including Poughquag and Lowerre Formation) - Gray, tan-weathering, medium-grained, generally well layered gneiss or feldspathic quartzite, composed of quartz, microcline, plagioclase, muscovite, biotite, and generally tourmaline; some schistose micaceous layers have sillimanite; commonly as quartz-sillimanite nodules rimmed with muscovite. Layers of purer quartzite in many areas, especially near the top or where the formation is thin.

Lithology: gneiss; quartzite

Basal marble member [of Walloomsac Schist] (Middle Ordovician) at surface, covers 0.6 % of this area

Basal marble member [of Walloomsac Schist] - Dark-gray to white, massive to layered schistose or phyllitic calcite-phlogopite marble.

Lithology: marble

Augen gneiss (Proterozoic Y) at surface, covers 0.1 % of this area

Augen gneiss (including local term "Danbury Gneiss;" equivalent in part to Tyringham Gneiss of Massachusetts) - Medium-gray to spotted, fine- to medium-grained, porphyritic, foliated and lineated granitic gneiss, composed of microcline (largely as megacrysts or augen up to 10 cm long), quartz, albite, or oligoclase, biotite and minor hornblende.

Lithology: augen gneiss

Partridge Formation (Middle Ordovician) at surface, covers < 0.1 % of this area

Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Sulfidic mica schist and subordinate amphibolite.

Lithology: mica schist; amphibolite

Tatnic Hill Formation (Ordovician or Proterozoic Z) at surface, covers < 0.1 % of this area

Tatnic Hill Formation - Fly Pond Member - Calc-silicate gneiss and marble.

Lithology: gneiss; marble

Trap Falls Formation plus Ordovician? granitic gneiss (Middle or Lower Ordovician) at surface, covers 1 % of this area

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.

Lithology: schist; granitic gneiss; gneiss; mica schist; granulite; amphibolite

Westerly Granite (Permian) at surface, covers < 0.1 % of this area

Westerly Granite - Light-gray, pink-weathering, fine-grained, massive, aplitic granite, composed of oligoclase or albite, quartz, and K-feldspar, with minor biotite and accessory muscovite, magnetite, allanite, and sphene.

Lithology: granite

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