Geologic units in Hampshire county, Massachusetts

New Haven Arkose (Upper Triassic) at surface, covers 18 % 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 17 % 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.

Waits River Formation (Lower Devonian) at surface, covers 8 % 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.

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

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

Goshen Formation (Lower Devonian) at surface, covers 5 % 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.

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

Reddish-brown to pale red conglomerate and arkose.

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.

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

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

Partridge Formation (includes Brimfield Schist of Emerson, 1917) (Middle Ordovician) at surface, covers 3 % of this area

Sulfidic mica schist and subordinate amphibolite.

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

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

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

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

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

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

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

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

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

Layered to massive biotite-feldspar gneiss and amphibolite.

Gray, well-layered biotite-plagioclase-quartz gneiss (Proterozoic Y) at surface, covers 1 % of this area

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

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

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

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

Undifferentiated Hoosac Formation.

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

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

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

Sulfidic mica schist and abundant amphibolite.

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

(Intrudes De) - Zone containing primary igneous orthopyroxene-augite quartz monzodiorite.

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

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

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

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

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

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

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).

Hawley Formation (Middle Ordovician) at surface, covers 0.6 % 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).

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

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

Mount Mineral Formation (Proterozoic Z) at surface, covers 0.6 % 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.

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

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).

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

Similar to Dg but having scattered beds of calcareous granofels.

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

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

Hawley Formation (Middle Ordovician) at surface, covers 0.5 % 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).

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

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

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

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

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

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.

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

Plagioclase gneiss and minor amphibolite.

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

Rowe Schist (Lower Ordovician and Cambrian) at surface, covers 0.3 % 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.

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

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

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

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

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

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

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

Massive granitic gneiss in cores of Warwick and Vernon domes.

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

Granofels and schist where mapped separately.

Paxton Formation (Silurian) at surface, covers 0.2 % 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).

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

Like Dgm but having a higher percentage of quartzite.

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.

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

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.

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

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

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

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).

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

Diabase dikes and sills.

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

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).

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

Amphibolite where mapped separately.

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

Partly associated with the Williamsburg Granodiorite.

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

Interpreted as tectonic slivers.

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

(Intrudes De) - Hornblendite.

Hawley Formation (Middle Ordovician) at surface, covers < 0.1 % 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).

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

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

Poplar Mountain Gneiss (Proterozoic Z) at surface, covers < 0.1 % 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.

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

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).

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

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

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

Green to dark-green greenstone or amphibolite.

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

Muscovite quartzite.

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

Bluish-gray weathering black sulfidic slate and chert.

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

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).

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

Although extremely narrow, shows local cross cutting relations with Ops, Sfs, and Dl.

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

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

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

(Intrudes De) - Inclusions of granofels (age uncertain).

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

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

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.

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.

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

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

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

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

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

Biotite-tourmaline schist and quartzite.

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).

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

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

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

(Intrudes De) - Biotite tonalite of marginal stocks.

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

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).

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

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

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

Amphibolite.

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.

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

(Intrudes De) - Hornblende peridotite.

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

Intruded near or along thrust faults. Intrudes CAZh and Proterozoic Y gneisses.