Geologic units in Franklin county, Massachusetts

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

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.

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

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).

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

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

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

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

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

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

Littleton Formation (Lower Devonian) at surface, covers 6 % of this area

Black to gray aluminous mica schist, quartzose schist, and aluminous phyllite.

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

Layered to massive biotite-feldspar gneiss and amphibolite.

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers 5 % of this area

Sulfidic mica schist and subordinate amphibolite.

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

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.

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

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

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

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

Pauchaug Gneiss (Ordovician) at surface, covers 3 % of this area

Massive granitic gneiss in cores of Warwick and Vernon domes.

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

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).

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

Amphibolite, felsic gneiss, garnet-amphibole quartzite, and marble too thin to show separately at map scale. Gedrite, anthophyllite, cummingtonite locally abundant in amphibolite layers.

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

Pale red conglomerate and arkosic sandstone, coarsens eastward. 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).

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

Like Dgm but having a higher percentage of quartzite.

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

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

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

Undifferentiated Hoosac Formation.

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

Undifferentiated Poplar Mountain and Dry Hill Gneisses .

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

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

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

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

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

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers 1 % of this area

Sulfidic mica schist and abundant amphibolite.

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

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

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

Pale red conglomerate and arkosic sandstone.

Erving Formation (Lower Devonian) at surface, covers 0.8 % of this area

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

Clough Quartzite (Upper Silurian) at surface, covers 0.8 % of this area

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).

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

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

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

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

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

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

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

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

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

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

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

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers 0.5 % of this area

Felsic gneiss of volcanic derivation and minor amphibolite.

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

White to buff quartzite and feldspathic quartzite commonly with biotite and/or actinolite.

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

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).

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

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

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

(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.

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

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

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

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

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

Amphibolite where mapped separately.

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

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

Hawley Formation (Middle Ordovician) at surface, covers 0.3 % of this area

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).

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers 0.2 % of this area

Sillimanite-feldspar augen gneiss.

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

Light-gray foliated microcline-plagioclase-quartz biotite gneiss containing microcline megacrysts. Intrudes Om.

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

(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.

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

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.

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

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

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

Pale red conglomerate and arkosic sandstone, coarsens eastward.

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

Amphibolite, hornblende schist.

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

Rusty-weathering, massive granofels containing anthophyllite and tourmaline; some rusty-stained gneiss.

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

White to very-light-green plagioclase granofels containing minor garnet. Plagioclase-hornblende-garnet gneiss containing hornblende blades and garnet 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).

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

(Intrudes De) - Outer zone of hornblende quartz monzodiorite gneiss.

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

Biotite-tourmaline schist and quartzite.

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

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

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

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).

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

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

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

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

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

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.

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

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).

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

Green to dark-green greenstone or amphibolite.

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

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

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

Biotite granitic gneiss.

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

Granite, granodiorite, and tonalite.

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

(Intrudes De) - Transition zone dominated by augite-hornblende quartz monzodiorite.

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

Diabase dikes and sills.

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

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).

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

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

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.

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

Dark-gray to grayish-black, rusty-weathering sulfidic slate and phyllite interlayered with felsic volcanic rocks and tuffs, and amphibolite (Opa). Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

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

Granofels and schist where mapped separately.

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

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).

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.

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

Partly associated with the Williamsburg Granodiorite.

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

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).

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

Containing beds of amphibolite, aluminous schist, quartzite, and calc-silicate gneiss.

Waits River Formation - muscovite porphyroblastic carbonaceous schist member (staurolite-grade rocks) (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Dark-gray to coaly-black, fine-grained plagioclase-muscovite-quartz schist and metawacke, shown southeast of Springfield; in part correlative with staurolite-grade rocks mapped as Littleton Formation (Dl) flanking the Vernon dome (shown as DSwb/Dl). Part of the Connecticut Valley Trough.

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

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

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

Slightly foliated.

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

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers < 0.1 % of this area

Lenses of ultramafic rock, commonly hornblendite with or without olivine, orthopyroxene, spinel, cummingtonite, anthophyllite, ilmenite and chlorite.

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

Lenses of peridotite, variously altered.

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

In Connecticut River bed, near French King Rock.

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

Interpreted as tectonic slivers.

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

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.

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

Hornblendite (ultramafic rock).

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

Basal quartzite and conglomerate.

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

Mostly foliated; intrudes Dl.

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

Amphibolite where mapped separately.

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

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

Clough Quartzite - quartzite and quartz-cobble metaconglomerate (Lower Silurian) at surface, covers < 0.1 % of this area

Quartzite and quartz-cobble metaconglomerate. Locally contains quartz-cobble conglomerate with abundant dark-gray phyllite matrix that resembles phyllite of the Littleton Formation. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

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

Metamorphosed limestone, calcareous sandstone, siltstone, and pelite. Some limestone conglomerate and polymict conglomerate with calcareous matrix. Locally equivalent to Madrid and Smalls Falls Formations in Chesterfield, N.H., area. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Waits River Formation - volcaniclastic rock member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Silvery-grayish-green to light-gray, muscovite-biotite (chlorite)-plagioclase-quartz schist and granofels. Part of the Connecticut Valley Trough.

Waits River Formation - slate and phyllite member (Lower Devonian and Upper Silurian) at surface, covers < 0.1 % of this area

Predominantly dark- to light-gray, lustrous, carbonaceous chlorite-biotite-muscovite-quartz slate, phyllite, or schist; contains thin beds of quartzite and only sparse layers of punky-weathering limestone. Shown south of the Pomfret dome where rocks typical of the Gile Mountain Formation are absent, and near Randolph. Part of the Connecticut Valley Trough.