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Mineral Resources > Online Spatial Data > Geology > by state > Massachusetts Geology

Geologic units in Hampshire county, Massachusetts

Belchertown Complex (age uncertain) at surface, covers < 0.1 % of this area

Belchertown Complex (intrudes De) - Inclusions of amphibolite (age uncertain).

Lithology: amphibolite

Goshen Formation (Lower Devonian) at surface, covers 17 % of this area

Goshen Formation - Well-bedded micaceous quartzite or quartz schist grading upward into light- to dark-gray, carbonaceous aluminous schist in beds 5 to 15 cm thick.

Lithology: schist; quartzite

Diabase dikes and sills (Lower Jurassic) at surface, covers 2 % of this area

Diabase dikes and sills.

Lithology: diabase

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers 1 % of this area

Hoosac Formation - Undifferentiated Hoosac Formation.

Lithology: schist; phyllite; gneiss; amphibolite; quartzite; granofels; calc-silicate rock

Serpentinite and/or talc rock (Precambrian to Phanerozoic) at surface, covers < 0.1 % of this area

Serpentinite and/or talc rock - Interpreted as tectonic slivers.

Lithology: serpentinite

East Berlin Formation (Lower Jurassic) at surface, covers 0.7 % of this area

East Berlin Formation - Reddish-brown to pale red arkosic sandstone and siltstone, and gray sandstone, gray mudstone, and black shale; interpreted as lake beds. Assigned to Newark Supergroup (Robinson and Luttrell, 1985). 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: sandstone; siltstone; mudstone; black shale

Belchertown Complex (Devonian) at surface, covers < 0.1 % of this area

Belchertown Complex (intrudes De) - Biotite tonalite of marginal stocks.

Lithology: tonalite

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

Hampden Basalt - Thin flows of quartz tholeiite, locally intimately associated with Granby Basaltic Tuff.

Lithology: tholeiite

New Haven Arkose (Upper Triassic) at surface, covers 18 % 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

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

East Berlin Formation - Pale red conglomerate and arkosic sandstone. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).

Lithology: conglomerate; sandstone

Hawley Formation (Middle Ordovician) at surface, covers 0.5 % of this area

Hawley Formation - Black, fine-grained, splintery, rusty-weathering schist and thin dark quartzite; interlayered amphibolite commonly has plagioclase megacrysts. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Lithology: schist; quartzite; amphibolite

Belchertown Complex (Devonian) at surface, covers < 0.1 % of this area

Belchertown Complex (intrudes De) - Hornblende peridotite.

Lithology: peridotite

Belchertown Complex (Precambrian to Paleozoic) at surface, covers < 0.1 % of this area

Belchertown Complex (intrudes De) - Inclusions of granofels (age uncertain).

Lithology: granofels

Waits River Formation (Lower Devonian) at surface, covers 8 % of this area

Waits River Formation - Interbedded medium- to dark-gray, moderately rusty weathering, highly contorted, unbedded schist and punky-weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.

Lithology: schist; granofels; marble

Belchertown Complex (Devonian) at surface, covers 0.9 % of this area

Belchertown Complex (intrudes De) - Zone containing primary igneous orthopyroxene-augite quartz monzodiorite.

Lithology: quartz monzodiorite

Dry Hill Gneiss (Proterozoic Z) at surface, covers 2 % of this area

Dry Hill Gneiss - Pink microcline-biotite and microcline-hornblende gneiss containing pink microcline megacrysts and minor quartzite.

Lithology: granitic gneiss; quartzite

Portland Formation (Lower Jurassic) at surface, covers 3 % 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

Holyoke Basalt (Lower Jurassic) at surface, covers 0.6 % 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

Fourmile Gneiss (Ordovician, Cambrian, or Proterozoic Z) at surface, covers 2 % of this area

Fourmile Gneiss - Layered to massive biotite-feldspar gneiss and amphibolite.

Lithology: biotite gneiss; amphibolite

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Moretown Formation - Green to dark-green greenstone or amphibolite.

Lithology: greenstone; amphibolite

Partridge Formation (Middle Ordovician) at surface, covers 3 % of this area

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

Lithology: mica schist; amphibolite

Belchertown Complex (Devonian) at surface, covers < 0.1 % of this area

Belchertown Complex (intrudes De) - Hornblendite.

Lithology: hornblendite

Mount Mineral Formation (Proterozoic Z) at surface, covers < 0.1 % of this area

Mount Mineral Formation (Probably correlates with Poplar Mountain Gneiss but is more aluminous) - Lenses of partially serpentinized harzburgite containing abundant veins of anthophyllite.

Lithology: peridotite; serpentinite

Moretown Formation (Middle Ordovician or older) at surface, covers 0.8 % of this area

Moretown Formation - Nubble garnet schist, pinstriped granofels, and fine-grained amphibolite in equal parts.

Lithology: schist; granofels; amphibolite

Dry Hill Gneiss (Proterozoic Z) at surface, covers 1 % of this area

Dry Hill Gneiss - Pelham Quartzite Member. White to buff quartzite and feldspathic quartzite commonly with biotite and/or actinolite.

Lithology: quartzite

Middlefield Granite (Devonian) at surface, covers 0.5 % of this area

Middlefield Granite - Moderately foliated, biotite-muscovite granite with microcline megacrysts. Intrudes OCAr and Om.

Lithology: granite

Gile Mountain Formation (Lower Devonian) at surface, covers 0.2 % of this area

Gile Mountain Formation - Like Dgm but having a higher percentage of quartzite.

Lithology: phyllite; schist; quartzite; granofels; marble

Goshen Formation (Lower Devonian) at surface, covers 5 % of this area

Goshen Formation - Light gray-brown micaceous quartzite and quartz-mica-garnet schist in beds as much as 6 m thick. Calc-silicate granofels and rare punky-weathering calcareous granofels.

Lithology: quartzite; schist; granofels

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

Clough Quartzite - Quartz-pebble conglomerate, quartzite, and minor mica schist and calc-silicate rocks. Fossils at Bernardston are similar to those at Croyden Mountain, New Hampshire which indicate late Llandoverian age. Parts of the Littleton and Partridge Formations, and Clough Quartzite in MA are here reassigned to the Rangeley Formation [here geographically extended to MA]. The four mapped areas of Clough Quartzite in the Amherst area west of the Connecticut Valley border fault are now interpreted as conglomerate lenses in the Rangeley. Clough is considered the key stratigraphic unit in Bronson Hill anticlinorium because 1) it is dominated by distinctive, readily recognizable rock types, 2) where present, it is base of Silurian-Devonian sequence, resting with detectable unconformity on older rocks, and 3) it contains late Llandoverian fossils at several localities in western NH and adjacent VT, and at Bernardston, MA. Consists mostly of quartz-pebble conglomerate in which pebbles are typically deformed; other lithologies are quartz grit or white to pink, well-bedded quartzite. Locally contains some mica schist beds. On the MA State bedrock geologic map (Zen and others, 1983), thickness is locally exaggerated because at many localities, the unit was only a few meters or less thick and could not be shown at a scale of 1:250,000. Maximum thickness is 200 m on west limb of Northfield syncline. Unconformably overlies Fourmile Gneiss in Pelham dome and in Kempfield anticline, or Ammonoosuc Volcanics over most gneiss domes. Partridge Formation occurs along Clough-Ammonoosuc contact as lenses in many areas (Hatch and others, 1988).

Lithology: conglomerate; quartzite; mica schist; calc-silicate rock

Belchertown Complex (Devonian) at surface, covers 5 % of this area

Belchertown Complex (intrudes De) - Outer zone of hornblende quartz monzodiorite gneiss.

Lithology: granitic gneiss

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

Rowe Schist - Fine- to medium-grained, well-layered and foliated amphibolite; epidote-rich layers locally abundant. Includes its typical Chester Amphibolite Member at Chester, Massachusetts.

Lithology: amphibolite

Hatch Hill Formation (Upper Cambrian) at surface, covers < 0.1 % of this area

Hatch Hill Formation - Bluish-gray weathering black sulfidic slate and chert.

Lithology: slate; chert

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

Shuttle Meadow Formation - Reddish-brown to pale red arkosic sandstone and siltstone, and gray sandstone, gray mudstone, and black shale; interpreted as lake beds. The Shuttle Meadow Formation is assigned to Newark Supergroup and is extended into MA in the Hartford basin. It consists of sandstone strata containing one interval of gray mudstone beds. The unit grades eastward along strike into a conglomeratic facies. It overlies the New Haven Arkose or Hitchcock Volcanics and underlies the Holyoke Basalt (Robinson and Luttrell, 1985).

Lithology: sandstone; siltstone; mudstone; black shale

Granby Basaltic Tuff (Lower Jurassic) at surface, covers 0.3 % of this area

Granby Basaltic Tuff - Friable, well-bedded dark tuff, commonly incorporating sediment fragments. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).

Lithology: tuff

Ammonoosuc Volcanics (Middle Ordovician) at surface, covers 0.8 % 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

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers 0.6 % of this area

Rowe Schist - Light-green to light-bluish-gray schist having thin granular quartz lenses and lamellae. Kyanite and staurolite typical at higher grades.

Lithology: schist

Belchertown Complex (Devonian) at surface, covers 0.4 % of this area

Belchertown Complex (intrudes De) - Intrusive breccia, mafic and ultramafic fragments in quartz diorite matrix.

Lithology: quartz diorite; breccia; mafic rock; ultramafic intrusive rock

Dry Hill Gneiss (Proterozoic Z) at surface, covers < 0.1 % of this area

Dry Hill Gneiss - Biotite-tourmaline schist and quartzite.

Lithology: schist; quartzite

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers 0.3 % of this area

Hoosac Formation - Lustrous greenish-gray schist characterized by 1-1.5 cm garnets; resembles Gassetts Schist of Vermont.

Lithology: schist

Silicified fault-breccia or strongly silicified metamorphic rocks (Lower Jurassic) at surface, covers < 0.1 % of this area

Silicified fault-breccia or strongly silicified metamorphic rocks.

Lithology: breccia; metamorphic rock

Shuttle Meadow Formation (Lower Jurassic) at surface, covers 0.1 % of this area

Shuttle Meadow Formation - Pale red conglomerate and arkosic sandstone. The Shuttle Meadow Formation is assigned to Newark Supergroup and is extended into MA in the Hartford basin. It consists of sandstone strata containing one interval of gray mudstone beds. The unit grades eastward along strike into a conglomeratic facies. It overlies the New Haven Arkose or Hitchcock Volcanics and underlies the Holyoke Basalt (Robinson and Luttrell, 1985).

Lithology: conglomerate; sandstone

Hitchcock Volcanics (Lower Jurassic) at surface, covers < 0.1 % of this area

Hitchcock Volcanics - Nested cones of basaltic breccia containing abundant fragments of New Haven Arkose (Jn, TRn), locally intrusive into arkose near base; overlain by lava flow of Holyoke Basalt (Jhb) and/or Shuttle Meadow Formation (Jsm).

Lithology: volcanic breccia (agglomerate); arkose

Collinsville Formation (Middle Ordovician or older) at surface, covers 0.4 % of this area

Collinsville Formation - Plagioclase gneiss and minor amphibolite.

Lithology: gneiss; amphibolite

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

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

Lithology: mica schist; amphibolite

Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z) at surface, covers 3 % of this area

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

Lithology: biotite gneiss; amphibolite; augen gneiss

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

Fourmile Gneiss - Muscovite quartzite.

Lithology: quartzite

Mount Mineral Formation (Proterozoic Z) at surface, covers 0.6 % of this area

Mount Mineral Formation (Probably correlates with Poplar Mountain Gneiss but is more aluminous) - Aluminous schist, amphibolite, and quartzite, undifferentiated; locally rich in garnet and kyanite, and with relict sillimanite and orthoclase from pre-Middle Ordovician metamorphism.

Lithology: schist; amphibolite; quartzite

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

Fitch Formation - Sulfidic calc-silicate and minor sulfidic schist. Although the text and figures of this report show the Fitch as Silurian, a footnote [added just before this report went to press] cites a change in age from Silurian to Early Devonian based on conodonts found at the Bernardston, MA, locality, as reported in Elbert and others (1988). In Bronson Hill anticlinorium in MA, Fitch occurs as lenses between Clough Quartzite and Littleton Formation. Most common rock types in MA are gray, massive to weakly bedded, quartz-labradorite-biotite granulite containing a moderate amount of some combination of calc-silicate minerals (calcic amphibole, zoisite or clinozoisite, diopside, sphene, and microcline); commonly interbedded with biotite-free granulite that contains same calc-silicate minerals. One small exposure consists of nearly pure calcite marble. Larger lenses of Fitch consist of varieties of schist, similar to Partridge Formation. Best exposures are in low hills west of village of Orange, northeast of junction of MA Hwys 2A and 78. As shown on MA State bedrock geologic map, Fitch everywhere overlies Clough Quartzite and is never in contact with Partridge. Fossils dating the Fitch as Pridolian (Harris and others, 1983) are all from Littleton, NH, area [however, see mention of footnote, above]. [Papers presented as chapters in U.S. Geological Survey Professional Paper 1366 are intended as explanations and (or) revisions to MA State bedrock geologic map of Zen and others (1983) at scale of 1:250,000.] (Hatch and others, 1988).

Lithology: calc-silicate rock; schist

Biotite-garnet-feldspar gneiss of Ragged Hill (Devonian) at surface, covers < 0.1 % of this area

Biotite-garnet-feldspar gneiss of Ragged Hill - Although extremely narrow, shows local cross cutting relations with Ops, Sfs, and Dl.

Lithology: gneiss

Feldspar-quartz-muscovite pegmatite (Devonian) at surface, covers < 0.1 % of this area

Feldspar-quartz-muscovite pegmatites - Partly associated with the Williamsburg Granodiorite.

Lithology: pegmatite

Paxton Formation (Silurian) at surface, covers 0.2 % of this area

Paxton Formation - Amphibolite. The Paxton, here of group rank, includes strata formerly mapped in CT as the Hebron Formation and in MA as the Paxton Formation. It conformably overlies the Oakdale Formation and structurally and conformably underlies the Brimfield Group. It is undivided in central MA; in northeast CT and adjacent MA it is divided into the Dudley and Southbridge Formations. Age is Late Proterozoic(?) based on the intrusion of 440 m.y. Hedgehog Hill gneiss into the overlying Brimfield Group and an age of 1188 m.y. for detrital zircons from the Paxton (Pease, 1989).

Lithology: amphibolite

Coys Hill Porphyritic Granite Gneiss (Lower Devonian) at surface, covers 0.1 % of this area

Coys Hill Porphyritic Granite Gneiss - Coarse-grained porphyritic microcline granite gneiss, commonly containing garnet and sillimanite with or without muscovite; continuous with the Cardigan and Ashuelot plutons of Kinsman Quartz Monzonite in New Hampshire; appears to be an early quasi-concordant intrusion within Dl.

Lithology: granitic gneiss

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers 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

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

Goshen Formation - Dg containing beds of punky-weathering calcareous granofels more than 15 cm thick near the contact with the Waits River Formation.

Lithology: schist; quartzite; granofels

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

Hoosac Formation - Greenish chlorite-albite-magnetite-sericite-quartz schist and granofels.

Lithology: mica schist; granofels

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

Hoosac Formation - Green to gray-green chlorite-sericite-quartz phyllite; interbeds of chloritoid- or albite-rich schist and minor quartzite, locally rich in garnet and kyanite.

Lithology: phyllite; schist; quartzite

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Lenses of ultramafic rock, commonly hornblendite with or without olivine, orthopyroxene, spinel, cummingtonite, anthophyllite, ilmenite and chlorite.

Lithology: ultramafic intrusive rock; hornblendite

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

Hawley Formation - Medium-gray plagioclase-hornblende-chlorite schist containing megacrysts of plagioclase and angular fragments of feldspar granofels, epidote-plagioclase granofels, and dark-gray amphibolite. As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Lithology: schist; granofels; amphibolite

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers 0.3 % of this area

Rowe Schist - Gray to black, fine-grained , slightly rusty, moderately carbonaceous schist; minor fine- to medium-grained dark-gray to white quartzite. Minor lenses of rock identical to OCAr.

Lithology: schist; quartzite

Portland Formation (Lower Jurassic) at surface, covers 4 % of this area

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

Lithology: conglomerate; arkose

Hardwick Tonalite (Lower Devonian) at surface, covers 0.7 % of this area

Hardwick Tonalite - Dark-gray, moderately to strongly foliated biotite tonalite to granodiorite gneiss; intrudes Dl.

Lithology: granitic gneiss

Belchertown Complex (Devonian) at surface, covers 1 % of this area

Belchertown Complex (intrudes De) - Transition zone dominated by augite-hornblende quartz monzodiorite.

Lithology: quartz monzodiorite

Erving Formation (Lower Devonian) at surface, covers 0.3 % of this area

Erving Formation - Biotite-plagioclase granofels, minor mica schist and calc-silicate granofels, and layers of epidote amphibolite.

Lithology: granofels; mica schist; amphibolite

New Haven Arkose (Lower Jurassic) at surface, covers 0.4 % 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. Assigned to Newark Supergroup (Robinson and Luttrell, 1985).

Lithology: arkose; siltstone; mudstone; conglomerate

Gneiss at Hallockville Pond (Ordovician) at surface, covers 0.2 % of this area

Gneiss at Hallockville Pond - Light-gray foliated microcline-plagioclase-quartz biotite gneiss containing microcline megacrysts. Intrudes Om.

Lithology: granitic gneiss

Moretown Formation (Middle Ordovician or older) at surface, covers 3 % of this area

Moretown Formation - Light-greenish-gray to buff, fine-grained, pinstriped granofels and schist.

Lithology: granofels; schist

Hawley Formation (Middle Ordovician) at surface, covers 0.6 % of this area

Hawley Formation - Interbedded amphibolite, greenstone, feldspathic schist and granofels. Coarse plagioclase in some amphibolite near top; local coarse hornblende blades or sprays. Sparse coticule (Emerson, 1917, p. 43). As used here the Hawley includes amphibolite, sulfidic rusty schists, abundant coticules, silvery schists, quartzites and quartz conglomerates, and quartz, feldspar, biotite granulites. The quartzites and quartz conglomerates occur at two positions in rocks here assigned to the Hawley. Those occurring near the top have been mapped previously as Russell Mountain Formation or as Shaw Mountain Formation. The Hawley overlies the Ordovician Barnard Gneiss and underlies Silurian and Devonian "calciferous schists" that include the westernmost Goshen Formation in MA and Northfield Formation in southern VT, the central Waits River Formation and the eastern Gile Mountain Formation. Authors believe that the Goshen, Northfield, and Waits River are facies equivalents, while the Gile Mountain is slightly younger. Map symbol indicates that Hawley is Ordovician and Silurian. 40Ar/3Ar hornblende release spectrum date of 433+/-3 Ma obtained by Spear and Harrison (1989) (Trzcienski and others, 1992).

Lithology: amphibolite; greenstone; schist; granofels

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

Cobble Mountain Formation - Thick-bedded (15 to 40 cm), nonrusty-weathering, silvery-gray, medium- to coarse-grained mica gneiss interlayered with nonrusty-weathering mica schist and minor amphibolite.

Lithology: gneiss; mica schist; amphibolite

Poplar Mountain Gneiss (Proterozoic Z) at surface, covers < 0.1 % of this area

Poplar Mountain Gneiss (Probably correlates with Mount Mineral Formation but is more feldspathic) - Basal quartzite, where thick enough to map; commonly feldspathic, containing biotite and actinolite or muscovite.

Lithology: quartzite

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

Ponaganset Gneiss - Gneissic biotite granite containing megacrysts of microcline; biotite in coarse streaks and patches. Equivalent to part of former Northbridge Granite Gneiss (usage now abandoned). 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: granite

Williamsburg Granodiorite (Devonian) at surface, covers 0.5 % of this area

Williamsburg Granodiorite - Equigranular biotite-muscovite granodiorite. Overprinting used in area where sufficient metasedimentary outcrop allows continuity in stratigraphic mapped. Intrudes Dg, Dw, Dgm, Dl, and De.

Lithology: granodiorite

Erving Formation (Lower Devonian) at surface, covers 0.2 % of this area

Erving Formation - Granofels and schist where mapped separately.

Lithology: granulite; schist

Moretown Formation (Middle Ordovician or older) at surface, covers < 0.1 % of this area

Moretown Formation - Light- to medium-gray, rusty, carbonaceous quartz-muscovite schist.

Lithology: mica schist

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

Erving Formation - Amphibolite where mapped separately.

Lithology: amphibolite

Littleton Formation (Lower Devonian) at surface, covers 2 % of this area

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

Lithology: schist; phyllite

Pauchaug Gneiss (Ordovician) at surface, covers 0.2 % of this area

Glastonbury Gneiss - Massive granitic gneiss in cores of Warwick and Vernon domes.

Lithology: granitic gneiss

Goshen Formation (Lower Devonian) at surface, covers 0.5 % of this area

Goshen Formation - Similar to Dg but having scattered beds of calcareous granofels.

Lithology: quartzite; schist; granofels

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

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

Gile Mountain Formation (Lower Devonian) at surface, covers 4 % of this area

Gile Mountain Formation - Gray, slightly rusty, poorly bedded phyllite and schist containing 20 cm to 2 m beds of light-gray, fine-grained quartzite, local punky-brown weathering calcareous granofels or quartzose marble, and pods and stringers of vein quartz.

Lithology: phyllite; schist; quartzite; granofels; marble