Geologic units in Cheshire county, New Hampshire

Additional scientific data in this geographic area

Upper part of Rangeley Formation (Lower Silurian (Llandoverian)) at surface, covers 21 % of this area

Rusty-weathering, pelitic schist, metasandstone, and local coarse-grained metasandstone lentils; calc-silicate pods common; minor coticule. Probably equivalent to member C of Rangeley Formation of Maine.

Granite, granodiorite, and tonalite (Late Ordovician) at surface, covers 14 % of this area

Granite, granodiorite, and tonalite.

Kinsman Granodiorite (Early Devonian) at surface, covers 11 % of this area

(Kinsman Quartz Monzonite of Billings, 1955) - Foliated granite, granodiorite, tonalite, and minor quartz diorite; large megacrysts of potassium feldspar characteristic; garnet locally abundant.

Lower part of Rangeley Formation (Lower Silurian (Llandoverian)) at surface, covers 9 % of this area

Gray, thinly laminated (5-25 mm) metapelite with local lentils of turbidites and thin quartz conglomerates in western New Hampshire. Sparse calc-silicate pods and coticule. Probably equivalent to member B of Rangeley Formation of Maine.

Concord Granite (Late Devonian) at surface, covers 5 % of this area

Gray two-mica granite, locally grading to tonalite.

Partridge Formation, undivided (Middle - Upper Ordovician) at surface, covers 4 % 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.

Spaulding Tonalite (Early Devonian) at surface, covers 3 % of this area

(Spaulding Quartz Diorite of Fowler-Billings, 1949) - Weakly foliated to nonfoliated, spotted biotite quartz diorite, tonalite, granodiorite, and granite; garnet and muscovite may or may not be present.

Ammonoosuc Volcanics, Bimodal volcanic rocks (Middle - Upper Ordovician) at surface, covers 3 % of this area

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

Oliverian Plutonic Suite - granodioritic to quartz dioritic gneissic (Late Ordovician) at surface, covers 3 % of this area

Granodioritic to quartz dioritic gneissic border phase of Oobg, perhaps in part metasomatic. Part of the Bronson Hill arch intrusive rocks.

Littleton Formation, undivided (Lower Devonian; Siegenian) at surface, covers 3 % 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.

Waits River Formation - muscovite porphyroblastic carbonaceous schist member (staurolite-grade rocks) (Lower Devonian and Upper Silurian) at surface, covers 3 % 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.

Partridge Formation (Upper Ordovician) at surface, covers 3 % 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.

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

Thinly or poorly bedded aluminous lower part, somewhat rusty. Rare quartzite lentils. Carrabassett Formation in northwestern Maine is probably correlative.

Biotite granite (Late Ordovician) at surface, covers 2 % of this area

Pink, moderately to weakly foliated.

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

Light-gray metaturbidite, lithologically identical to, and probably correlative with, the Seboomook Formation of Maine. Coticule layers common.

Kinsman Quartz Monzonite of Billings (1955) (Early Devonian) at surface, covers 1 % of this area

Medium- to coarse-grained, potassium-feldspar-megacrystic, biotite granodiorite gneiss of the Ashuelot pluton. U-Pb zircon age of 403±2 Ma (R.D. Tucker, USGS, written commun., 2008). Part of the Bronson Hill arch intrusive rocks.

Bethlehem Granodiorite (Early Devonian) at surface, covers 1 % of this area

(Bethlehem Gneiss of Billings, 1955) - Gray, strongly foliated biotite-muscovite granodiorite and associated tonalite and granite.

Ammonoosuc Volcanics of Billings (1935) - undivided (Upper and Middle Ordovician) at surface, covers 1 % of this area

A heterogeneous unit of interlayered and interfingering metamorphosed volcanic, volcaniclastic, and sedimentary rocks. Compositions range from basalt to sodic rhyolite. Fragmental rocks dominate (tuff to tuff breccia), but include sparse mafic pillow lava and felsic lava. Sedimentary protoliths include dark-gray sulfidic shale, ironstone, siltstone, graywacke, volcanic conglomerate, and rare limestone. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Madrid and Smalls Falls Formations, undivided (Silurian) at surface, covers 0.9 % of this area

Madrid and Smalls Falls Formations, undivided.

Granite, granodiorite, and trondhjemite (Late Ordovician) at surface, covers 0.9 % of this area

Granite, granodiorite, and trondhjemite.

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

Medium-dark- to dark-gray slate interlayered with light-gray, fine-grained micaceous quartzite; in southeastern Vermont near the Vernon dome Dl is equated with DSwb and may be older than in the Bradford area. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Rangeley Formation (Lower Silurian) at surface, covers 0.7 % of this area

Interlayered, commonly rusty-weathering quartz-feldspar micaceous granofels and dark-gray mica schist containing porphyroblasts of garnet, staurolite, and kyanite. Calc-silicate lenses common in the granofels; granule and pebble metaconglomerate locally are present. Part of Piermont and other allochthons.

Fitch and Clough Formations, undivided (Silurian) at surface, covers 0.6 % of this area

Fitch and Clough Formations, undivided.

Perry Mountain and Rangeley Formations, undivided (Silurian) at surface, covers 0.6 % of this area

Perry Mountain and Rangeley Formations, undivided.

Member C (uppermost) of the Rangeley Formation in Maine and northeastern and southwestern New Hampshire (Lower Silurian (Llandoverian)) at surface, covers 0.5 % of this area

Quartz-pebble conglomerate overlain by rusty metapelite and feldspathic quartzite.

Clough Quartzite (Lower Silurian (upper Llandoverian)) at surface, covers 0.4 % 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.

Bethlehem Gneiss (Early Devonian) at surface, covers 0.3 % of this area

Medium- to coarse-grained, equigranular to porphyritic, muscovite-biotite-microcline-plagioclase metaquartz monzonite; contains garnet, sillimanite-andalusite and cordierite; intrudes rocks of the Rangeley Formation in New Hampshire. U-Pb zircon age of 407±5 Ma, no. 43 (Kohn and others, 1992) at Bellows Falls. Part of the Bronson Hill arch intrusive rocks.

Fitch Formation (Lower Devonian and Upper Silurian) at surface, covers 0.3 % 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.

Clough Quartzite - quartzite and quartz-cobble metaconglomerate (Lower Silurian) at surface, covers 0.3 % 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.

Rangeley Formation, Pink to green calc-silicate and purple biotite granofels (Lower Silurian (Llandoverian)) at surface, covers 0.3 % of this area

Thinly bedded. Close to transition from lower to upper parts of the Rangeley Formation. Probably equivalent to part of Paxton Formation of Zen and others (1983) in Massachusetts.

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

Within unit Sr; rusty sulfidic schist occurs in Fall Mountain nappe near Bellows Falls. Part of Piermont and other allochthons.

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.

Fitch Formation (Upper Silurian; Pridolian and Ludlovian) (Upper Silurian - (Pridolian and Ludlovian)) at surface, covers 0.1 % of this area

Metamorphosed limestone, calcareous sandstone, siltstone, and dark pelitic schist; lower contact is disconformable on the Clough Quartzite. Fossiliferous.

Trondhjemite (Late Ordovician) at surface, covers < 0.1 % of this area

Contains biotite and hornblende.

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

Amphibolite. Stratified rocks of the Bronson Hill arch and Sawyer Mountain belt.

Granite and trondhjemite dikes of Chester and Athens domes and west of the Connecticut Valley trough (Devonian) at surface, covers < 0.1 % of this area

Light-gray to white, garnet-muscovite-biotite granodiorite at Gassetts quarry, having a U-Pb zircon SHRIMP age of 392±6 Ma, no. 46 (Aleinikoff and others, 2011), from rims on Proterozoic-age cores (J.N. Aleinikoff, USGS, written commun., 2002); and whitish-gray muscovite-rich quartz monzonite and granodiorite, granite pegmatite, and aplite which occur as crosscutting nonfoliated dikes within the core of the domes and as folded and well-foliated dikes on the east and west flanks of the domes; also granite dikes and small stocks of very light gray to white, muscovite-rich, locally garnet-bearing, fine- to medium-grained biotite-muscovite quartz monzonite and granodiorite, locally orbicular, that intrude cover rocks east of the Green Mountain massif from Jamaica to Northfield, including the Liberty Hill locality and the granodiorite stock east of Plymouth. The latter contains inherited zircon with rims having an imprecise SHRIMP age of about 380 to 390 Ma (Aleinikoff and others, 2011); a similar dike south of Plymouth has a U-Pb zircon SHRIMP age of 365±5 Ma, no. 49 (Aleinikoff and others, 2011). These closely resemble undated white granodiorites of the Bethel area and dikes in the Chester and Athens domes; also resemble small dikes of granite, trondhjemite, and quartz monzonite largely west of the Connecti-cut Valley trough. Devonian granitic rocks of southern Vermont. Part of the New Hampshire Plutonic Suite.

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.

Hypersthene-biotite quartz diorite and hornblende or actinolite diorite or gabbro (Early Devonian - Late Devonian) at surface, covers < 0.1 % of this area

Spatially associated with Spaulding Tonalite plutons.

Perry Mountain Formation, undivided (Lower? - Middle? Silurian) at surface, covers < 0.1 % of this area

Sharply interbedded quartzites, light-gray nongraphitic metapelite, and "fast-graded" meta-turbidites. Coticule layers common.

Rangeley Formation - quartz conglomerate (Lower Silurian) at surface, covers < 0.1 % of this area

Within unit Sr; quartz conglomerate occurs in Fall Mountain nappe near Bellows Falls. Part of Piermont and other allochthons.