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Geologic units in Franklin county, Massachusetts

Poplar Mountain Gneiss (Proterozoic Z) at surface, covers 1 % of this area

Poplar Mountain Gneiss (Probably correlates with Mount Mineral Formation but is more feldspathic) - Biotite gneiss where mapped separately.

Lithology: biotite gneiss

Moretown Formation (Middle Ordovician or older) at surface, covers 0.5 % of this area

Moretown Formation - Buff to gray, medium- to coarse-grained, poorly bedded mica-rich schist showing dark-green chlorite clots. Some pinstriped granofels.

Lithology: mica schist; granofels

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

Littleton Formation - Gray slate and phyllite containing interbeds of gray schistose quartzite 1/4 inch to 6 inches thick. West of Guildhall are lustrous, light to dark gray biotite-garnet phyllite and schist, some slate, and subordinate quartzite and impure quartzite. South of Bellows Falls gray phyllite passes eastward into gray mica schist containing porphyroblasts of biotite, garnet, and staurolite.

Lithology: slate; phyllite; quartzite; schist; mica schist

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

Monson Gneiss - Amphibolite where mapped separately.

Lithology: amphibolite

Waits River Formation (Lower Devonian) at surface, covers 1 % of this area

Waits River Formation - Dw containing thick (1 m) beds of calcareous granofels. Mapped only in Colrain quadrangle; included in Dw elsewhere.

Lithology: schist; granofels; marble

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

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

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

Lithology: gneiss

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

Sugarloaf Formation - Pale red conglomerate and arkosic sandstone, coarsens eastward.

Lithology: conglomerate; sandstone

Erving Formation (Lower Devonian) at surface, covers < 0.1 % 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 0.3 % of this area

Erving Formation - Amphibolite where mapped separately.

Lithology: amphibolite

Littleton Formation (Lower Devonian) at surface, covers 5 % 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 3 % of this area

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

Lithology: granitic gneiss

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Felsic gneiss of volcanic derivation and minor amphibolite.

Lithology: felsic gneiss; amphibolite

Hawley Formation (Middle Ordovician) at surface, covers 3 % 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

Poplar Mountain Gneiss (Proterozoic Z) at surface, covers 0.4 % 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

Gile Mountain Formation (Lower Devonian) at surface, covers 0.1 % of this area

Gile Mountain Formation - Amphibolite, hornblende schist.

Lithology: amphibolite; amphibole schist

Belchertown Complex (Devonian) at surface, covers < 0.1 % 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 0.8 % 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

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

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

Waits River Formation - Amphibolite or hornblende schist locally containing conspicuous hornblende or garnet megacrysts. Rocks mapped as Conway Schist by Emerson (1898, 1917) and subsequently subdivided by Segerstrom (1956) and Willard (1956) were mapped across the MA-VT State line as Waits River and Gile Mountain Formations by Doll and others (1961) on Centennial Geologic Map of Vermont. Although controversy still exists over relative ages, detailed reconnaissance mapping by authors and S.F. Clark, Jr., L.M. Hall, and J.W. Pferd shows that Waits River and Gile Mountain Formations are readily distinguished in the field. For these reasons, and to maintain continuity across the State line, authors chose to follow VT nomenclature on here and on MA State bedrock geologic map (Zen and others, 1983). Primary difference between Waits River and Gile Mountain is presence in Gile Mountain of beds of noncalcareous, commonly micaceous quartzite. Both formations contain conspicuous beds of punky brown-weathering impure marble or calcareous granulite, mostly in Waits River and less abundant in Gile Mountain. Predominant lithology of both formations is typically contorted gray, graphitic, locally very sulfidic, moderately aluminous mica schist containing quartz veins. Gradational but definitely significant boundary can be mapped between both formations. Amphibolite in both formations may correlate with Standing Pond Volcanics occurring at or near Waits River-Gile Mountain contact in VT. Report goes into great detail regarding informal subdivision of each formation. Rocks previously mapped as Waits River Formation northeast of Shelburne Falls dome by Hatch and Hartshorn (1968) are here reassigned to an unnamed member of Goshen Formation because the rocks are indistinguishable from the Goshen. Goshen-Waits River contact is defined as the line along which, going eastward, the schist changes from aluminous, planar-bedded, and virtually quartz-free (Goshen), to alumina-poor, contorted, and rich in quartz veins (Waits River) (Hatch and others, 1988).

Lithology: amphibolite; amphibole schist

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

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

Hoosac Formation - Rusty, gray, quartz-albite-mica (-chlorite) schist and gneiss. Locally conglomeratic.

Lithology: mica schist; gneiss

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

Mount Toby Formation (Lower Jurassic) at surface, covers 2 % of this area

Mount Toby Formation - Breccia of amphibolite at Whitmore Ferry; interpreted as landslide deposit. The Mount Toby Conglomerate is here revised and renamed the Mount Toby Formation of the Newark Supergroup. It includes only the sedimentary strata in the Deerfield basin above the slump zone unconformity defined by Cornet (1977), or its projected equivalent at its contact with the underlying Turners Falls Sandstone. It includes conglomerates at the type locality, landslide deposits within the conglomerate, and sandstone and lake beds above the slump zone unconformity, which were formerly included in the Turners Falls Sandstone. Other rocks mapped as Mount Toby Conglomerate by Emerson (1898) in the Hartford, Deerfield, and Northfield basins have been assigned to the Portland, Sugarloaf, and Turners Falls Formations. Age is Sinemurian and Pliensbachian, based on the discovery by Cornet (1977) of palynoflora in these strata (Robinson and Luttrell, 1985).

Lithology: sedimentary breccia

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

Monson Gneiss - Lenses of peridotite, variously altered.

Lithology: peridotite

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

Cooleyville Granitic Gneiss - Biotite tonalite to granite in composition, strongly foliated and lineated; contains inclusions of Dpgb; intrudes Dl.

Lithology: tonalite; granite; gabbro

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 0.4 % 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

Prescott Complex (Devonian) at surface, covers 0.3 % of this area

Prescott Complex - Hornblende gabbro (formerly Prescott Diorite of Emerson, 1917).

Lithology: gabbro

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

Fitch Formation - Calc-silicate granofels, biotite granofels, minor sulfidic schist and marble. Correlated with the fossiliferous Fitch Formation of western New Hampshire. 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] (Hatch and others, 1988).

Lithology: granofels; schist; marble

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 < 0.1 % 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

Hoosac Formation (Lower Cambrian and Proterozoic Z) at surface, covers 0.4 % of this area

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

Lithology: mica schist; granofels

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

Goshen Formation (Lower Devonian) at surface, covers 3 % 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

Sherman Marble (Proterozoic Y) at surface, covers < 0.1 % of this area

Sherman Marble - White, coarse-grained graphite dolomite-calcite marble at Sherman Reservoir at the State line.

Lithology: marble

Turner Falls Sandstone (Lower Jurassic) at surface, covers 2 % of this area

Turner Falls Sandstone - Reddish-brown to pale red arkosic sandstone, and gray sandstone, gray siltstone, and black shale interpreted as lake beds.

Lithology: sandstone; siltstone; black shale

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

Collinsville Formation - Interlayered amphibolite and white felsic gneiss containing biotite, hornblende, and magnetite. Local calc-silicate beds. Coticule-bearing granofels, muscovite quartzite and amphibolite in upper part.

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

Collinsville Formation (Middle Ordovician or older) at surface, covers 0.1 % 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

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

Biotite granitic gneiss.

Lithology: granitic gneiss

Monson Gneiss (Ordovician, Cambrian, or Proterozoic Z) at surface, covers 7 % of this area

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

Lithology: biotite gneiss; amphibolite; augen gneiss

Poplar Mountain Gneiss (Proterozoic Z) at surface, covers 0.5 % of this area

Poplar Mountain Gneiss (Probably correlates with Mount Mineral Formation but is more feldspathic) - Dark biotite gneiss containing white microcline megacrysts and beds of quartzite.

Lithology: biotite gneiss; quartzite

Mount Mineral Formation (Proterozoic Z) at surface, covers 0.2 % 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

Granite, granodiorite, and tonalite (Late Ordovician) at surface, covers < 0.1 % of this area

Granite, granodiorite, and tonalite.

Lithology: granite; granodiorite; tonalite

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

Dry Hill Gneiss - Biotite-tourmaline schist and quartzite.

Lithology: schist; quartzite

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

Partridge Formation, undivided - Black, rusty-weathering sulfidic-graphitic slate or schist and sparse to abundant metagraywacke. Lies stratigraphically between upper and lower parts of the Ammonoosuc Volcanics.

Lithology: slate; schist; metasedimentary rock

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

Fine-grained hornblende diorite (Precambrian to Paleozoic) at surface, covers < 0.1 % of this area

Fine-grained hornblende diorite - In Connecticut River bed, near French King Rock.

Lithology: diorite

Putney Volcanics (Lower Devonian) at surface, covers < 0.1 % of this area

Putney Volcanics - Light greenish-gray plagioclase-quartz-muscovite phyllite and granofels.

Lithology: phyllite; granofels

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

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

Lithology: granitic gneiss

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

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

Ammonoosuc Volcanics (Middle Ordovician) at surface, covers 3 % 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

Mount Toby Formation (Lower Jurassic) at surface, covers 0.6 % of this area

Mount Toby Formation - Reddish-brown to pale red arkosic sandstone, and gray sandstone, gray siltstone, and black shale interpreted as lake beds.

Lithology: arkose; sandstone; siltstone; black shale;

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers 0.5 % 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

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

Collinsville Formation - Felsic gneiss containing scattered biotite, magnetite, garnet and hornblende. Local beds of amphibolite.

Lithology: felsic gneiss; amphibolite

Undifferentiated Poplar Mountain and Dry Hill Gneisses (Proterozoic Z) at surface, covers 1 % of this area

Undifferentiated Poplar Mountain and Dry Hill Gneisses .

Lithology: gneiss; biotite gneiss; quartzite; schist

Dry Hill Gneiss (Proterozoic Z) at surface, covers 0.4 % of this area

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

Lithology: quartzite

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

Partridge Formation - Rusty weathering carbonaceous mica schist locally containing porphyroblasts of biotite, garnet, or staurolite. (Southeastern Vermont).

Lithology: mica schist

Goshen Formation (Lower Devonian) at surface, covers 0.2 % 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 0.8 % 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

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

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

Lithology: phyllite; schist; quartzite; granofels; marble

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

Clough Quartzite - Orthoquartzite, quartz metaconglomerate, muscovite schist, minor polymictic metaconglomerate. Disconformable below Fitch Formation and unconformable on Ordovician formations. Equivalent, in part, to member C of Rangeley Formation of Maine. Fossiliferous.

Lithology: quartzite; meta-conglomerate; mica schist

Partridge Formation (Middle Ordovician) at surface, covers 5 % of this area

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

Lithology: mica schist; amphibolite

Moretown Formation (Middle Ordovician or older) at surface, covers 0.6 % of this area

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

Lithology: schist; granofels; amphibolite

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

Ammonoosuc Volcanics - Basal quartzite and conglomerate.

Lithology: quartzite; conglomerate

Dry Hill Gneiss (Proterozoic Z) at surface, covers 6 % of this area

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

Lithology: granitic gneiss; quartzite

Biotite-muscovite granite (Devonian) at surface, covers < 0.1 % of this area

Biotite-muscovite granite - Slightly foliated.

Lithology: granite

Turner Falls Sandstone (Lower Jurassic) at surface, covers 0.8 % of this area

Turner Falls Sandstone - Pale red conglomerate and arkosic sandstone.

Lithology: conglomerate; sandstone

Fourmile Gneiss (Ordovician, Cambrian, or Proterozoic Z) at surface, covers 5 % 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

Sugarloaf Formation (Lower Jurassic) at surface, covers 0.4 % of this area

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

Lithology: arkose; sandstone; siltstone; black shale

Partridge Formation (Middle Ordovician) at surface, covers 0.2 % of this area

Partridge Formation (includes Brimfield Schist of Emerson, 1917) - Sillimanite-feldspar augen gneiss.

Lithology: augen gneiss

New Haven Arkose (Upper Triassic) at surface, covers 7 % 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

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

Collinsville Formation - Interlayered amphibolite and felsic gneiss in beds less than 1 m thick. Local, coarse-grained magnetite-hornblende gneiss.

Lithology: amphibolite; felsic gneiss; mafic gneiss

Hawley Formation (Middle Ordovician) at surface, covers 0.4 % 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

Waits River Formation (Lower Devonian) at surface, covers 12 % 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

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

Mount Toby Formation - Breccia of granitic gneiss at Taylor Hill; interpreted as landslide deposit. The Mount Toby Conglomerate is here revised and renamed the Mount Toby Formation of the Newark Supergroup. It includes only the sedimentary strata in the Deerfield basin above the slump zone unconformity defined by Cornet (1977), or its projected equivalent at its contact with the underlying Turners Falls Sandstone. It includes conglomerates at the type locality, landslide deposits within the conglomerate, and sandstone and lake beds above the slump zone unconformity, which were formerly included in the Turners Falls Sandstone. Other rocks mapped as Mount Toby Conglomerate by Emerson (1898) in the Hartford, Deerfield, and Northfield basins have been assigned to the Portland, Sugarloaf, and Turners Falls Formations. Age is Sinemurian and Pliensbachian, based on the discovery by Cornet (1977) of palynoflora in these strata (Robinson and Luttrell, 1985).

Lithology: sedimentary breccia

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

Ammonoosuc Volcanics - Hornblendite (ultramafic rock).

Lithology: hornblendite

Ammonoosuc Volcanics, Bimodal volcanic rocks (Middle - Upper Ordovician) at surface, covers < 0.1 % of this area

Ammonoosuc Volcanics, Bimodal volcanic rocks - Locally includes unmapped Oals.

Lithology: bimodal suite

Goshen Formation (Lower Devonian) at surface, covers 7 % 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

Deerfield Basalt (Lower Jurassic) at surface, covers 0.6 % of this area

Deerfield Basalt - Well-jointed quartz tholeiite, locally vesicular and locally pillowed near base.

Lithology: tholeiite

Diabase dikes and sills (Lower Jurassic) at surface, covers 0.1 % of this area

Diabase dikes and sills.

Lithology: diabase

Collinsville Formation (Middle Ordovician or older) at surface, covers 1.0 % of this area

Collinsville Formation - Homogeneous garnetiferous biotite gneiss containing chlorite as clots and halos around garnet.

Lithology: biotite gneiss

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

Littleton Formation undivided - Gray metapelite and metawacke and subordinate metavolcanic rocks; generally, but not everywhere, conformable with underlying Fitch or Madrid Formations. Fossiliferous in western New Hampshire.

Lithology: metasedimentary rock; metavolcanic rock

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