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

Geologic units in Essex county, Vermont

Essexitite (Permian-Triassic) at surface, covers < 0.1 % of this area

Essexitite

Lithology: gabbro

Undifferentiated Granitic Rocks (Ordovician) at surface, covers 2 % of this area

Undifferentiated granitic rocks.

Lithology: granite

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

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

Lithology: mica schist

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

Ammonoosuc Volcanics, Felsic metavolcanic rocks.

Lithology: felsic metavolcanic rock

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

Gile Mountain Formation, Amphibolite - Hornblende-quartz-biotite-chlorite rock.

Lithology: amphibolite

Hornblende granite to granodiorite (Late Ordovician) at surface, covers < 0.1 % of this area

Hornblende granite to granodiorite - Part of Lost Nation pluton of northwestern New Hampshire.

Lithology: granite; granodiorite

Waits River Formation (Devonian) at surface, covers 0.6 % of this area

Waits River Formation - Gray quartzose and micaceous crystalline limestone weathered to distinctive brown earthy crust; interbedded and intergradational with gray quartz-muscovite phyllite or schist. Where more metamorphosed the limestones contain actinolite, hornblende, zoisite, diopside, wollastonite, and garnet, and the phyllite and schist, biotite, garnet, and locally andalusite, kyanite or sillimanite.

Lithology: limestone; phyllite; mica schist

Frontenac Formation, Mixed volcanic and sedimentary facies (Silurian?) at surface, covers < 0.1 % of this area

Frontenac Formation, Mixed volcanic and sedimentary facies.

Lithology: metavolcanic rock; metasedimentary rock

Smalls Falls Formation, undivided (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers < 0.1 % of this area

Smalls Falls Formation, undivided -Very rusty weathering, thinly bedded sulfidic-graphitic schist and pyrrhotitic calc-silicate granofels. Eastern facies equivalent to lower part of the Fitch Formation. Locally mapped as Francestown Formation of Nielson (1981) in southern New Hampshire.

Lithology: schist; granofels

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

Clough Formation - Quartzite, quartz-conglomerate, and mica schist; lenses of fossiliferous calcareous quartzite in upper part. (Southeastern Vermont).

Lithology: conglomerate; quartzite; mica schist

Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments (Upper to Middle Silurian (Ludlovian and Wenlockian)) at surface, covers < 0.1 % of this area

Smalls Falls Formation, Mixed metavolcanic rocks and metavolcanic sediments.

Lithology: metavolcanic rock

Ironbound Mountain Formation, undivided (Lower Devonian) at surface, covers < 0.1 % of this area

Ironbound Mountain Formation, undivided - Interbedded gray phyllite, in places containing feldspathic clasts, and feldspathic metasandstone, variably graded.

Lithology: phyllite; metasedimentary rock

Frontenac Formation, undivided (Silurian?) at surface, covers < 0.1 % of this area

Frontenac Formation, undivided - Interbedded thick feldspathic wackes, tan and green slates, and minor calcareous lenses.

Lithology: metasedimentary rock; slate

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

Fitch Formation - Quartz-plagioclase-biotite granulite; actinolite-diopside granulite; impure limestone and dolomite; mica schist; the carbonate-rich beds are typically an inch or two thick and segmented so as to give the weathered outcrop a characteristic pitted appearance. (Southeastern Vermont).

Lithology: granulite; limestone; dolostone (dolomite); mica schist

Gile Mountain Formation, Meetinghouse Slate Member (Devonian) at surface, covers 0.4 % of this area

Gile Mountain Formation, Meetinghouse Slate Member - Chiefly gray slate or phyllite characterized by beds of gray schistose quartzite 1/8 inch to 3 inches thick. Gile Mountain Formation and its Meetinghouse Slate Member were previously considered to be Early Devonian based on Emsian plant fossils from Compton Formation of QUE (Hueber and others, 1990; Hatch, 1991). Age assignment here changed to Early Devonian(?) because recent mapping indicates that Gile Mountain and Compton are not coextensive across VT-QUE border as formerly believed by Doll and others (1961, State map) and St. Julien and Slivitsky (1987). Instead, the formations are separated by Ironbound Mountain Formation. Ironbound Mountain Formation is conformably overlain by Compton, but it is not yet known whether Ironbound Mountain is overlain or underlain by Gile Mountain; this is shown by queried Ironbound Mountain-Gile Mountain contact in area of Averill 7.5-min quad, VT. Correlation of Gile Mountain and Compton is justified only if Gile Mountain in this area conclusively is shown to be underlain by Ironbound Mountain; otherwise, Gile Mountain (with possible exception of its Meetinghouse Slate Member) would be coeval with Silurian Frontenac Formation. Hatch (1988) proposed that Meetinghouse represents upper part of Gile Mountain on basis of graded bedding seen south of map area. This relationship is not proven, however, because Gile Mountain-Meetinghouse contact is difficult to define and graded beds are not always easily interpreted. On this map, Meetinghouse is tentatively shown to occur below main body of Gile Mountain on basis of remarkable similarity between it and Ironbound Mountain Formation. This relationship easily explains highly pelitic character of the Meetinghouse with upward-coarsening character of Lower Devonian sequences elsewhere in map area. Meetinghouse Slate Member includes volcanic facies (Moench and others, 1995).

Lithology: slate; phyllite; quartzite

Gile Mountain Formation, Hall Stream Member (Devonian) at surface, covers < 0.1 % of this area

Gile Mountain Formation, Hall Stream Member - Highly feldspathic grit, probably volcanic; feldspathic chlorite-ankerite schist and amphibolite; all northeast of Nulhegan River.

Lithology: schist; amphibolite

Littleton Formation (Devonian) at surface, covers 0.2 % 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

Undifferentiated Granitic Gneiss (Devonian) at surface, covers 34 % of this area

Undifferentiated Granitic Gneiss - Small dikes and sills do not show.

Lithology: granitic gneiss

Granites (Permian-Triassic) at surface, covers < 0.1 % of this area

Granites - Biotite and hornblende granites.

Lithology: granite

Waits River formation, Standing Pond Volcanic Member (Devonian) at surface, covers < 0.1 % of this area

Waits River formation, Standing Pond Volcanic Member - Amphibolite, garnet amphibolite, coarse garnet schist with fasciculitic hornblende, and hornblende maculite; contains pillow lavas near St. Johnsbury and passes eastward into actinolitic greenstone and greenstone south of Windsor.

Lithology: amphibolite; schist; greenstone

Syenite (Permian-Triassic) at surface, covers 0.8 % of this area

Syenite - Hornblende, biotite, quartz and augite syenites.

Lithology: syenite; quartz syenite

Ammonoosuc Volcanics (Ordovician) at surface, covers 0.4 % of this area

Ammonoosuc Volcanics - Fine-grained chloritic and biotitic gneiss and greenstone in areas north of Bellows Falls; biotite gneiss and amphibolite south of Bellows Falls. (Southeastern Vermont).

Lithology: biotite gneiss; greenstone; amphibolite

Tonalite, diorite, granodiorite, and granite (Late Ordovician ) at surface, covers 0.1 % of this area

Tonalite, diorite, granodiorite, and granite - More mafic rocks have hornblende; part of Lost Nation pluton.

Lithology: tonalite; diorite; granodiorite; granite

Pink equigranular biotite granite (Late Devonian) at surface, covers < 0.1 % of this area

Pink equigranular biotite granite - Found in Woodsville and Whitefield quadrangles and in small intrusive units in northern and southeastern New Hampshire.

Lithology: granite

Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire (Lower Devonian) at surface, covers < 0.1 % of this area

Ironbound Mountain Formation, Grits at Halls Stream in northern New Hampshire - Thickly bedded feldspathic volcaniclastic grit and interbedded gray slate. Equivalent to Grenier Ponds Member of the Ironbound Mountain Formation in western Maine.

Lithology: metavolcanic rock; slate

Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite (Silurian?) at surface, covers < 0.1 % of this area

Frontenac Formation, Graded-bedded metagraywacke and subordinate gray phyllite.

Lithology: metasedimentary rock; phyllite

Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon (Lower?- Middle? Silurian) at surface, covers < 0.1 % of this area

Perry Mountain Formation, Sedimentary and subordinate distal felsic and mafic volcanic facies in Piermont allochthon.

Lithology: metasedimentary rock; felsic metavolcanic rock; mafic metavolcanic rock

Gile Mountain Formation (Devonian) at surface, covers 36 % of this area

Gile Mountain Formation - Gray quartz-muscovite phyllite or schist, interbedded and intergradational with gray micaceous quartzite (graywacke northeast of Nulhegan River), calcareous mica schist, and, locally, quartzose and micaceous crystalline limestone like that of the Waits River formation. The phyllite and schist commonly contain porphyroblasts of biotite, garnet, or staurolite, and locally kyanite, andalusite, or sillimanite. Used as Early Devonian Gile Mountain Formation. Generally consists of gray to tan metawacke and schist or phyllite, gradational into its Meetinghouse Slate Member, but much more thickly bedded and less pelitic. Contains minor metavolcanic lentils. Unnamed metavolcanic member is possibly equivalent to Putney Volcanics of southeastern VT. Separately mapped interbedded gray slate or phyllite and brown-weathering calcite-ankerite metasiltstone, and minor marble and quartzite, resembles Waits River Formation of VT. Meetinghouse Slate Member consists of gray to black phyllite and silty metasandstone turbidite. Report includes geologic map, cross sections, correlation chart, and four 1:500,000-scale derivative maps (Lyons and others, 1997).

Lithology: phyllite; mica schist; quartzite; limestone; graywacke

Albee Formation (Ordovician) at surface, covers 23 % of this area

Albee Formation - Massive, gray, white-weathered quartzite and feldspathic quartzite interbedded with greenish-gray slate, phyllite, feldspthic phyllite and quartzose argillaceous phyllite. Micaceous quartzite, quartz-mica schist, mica schist and hornfels contining porphyroblasts of biotite, garnet, staurolite and sillimanite in the vicinity of granitic plutons. Soda-rhyolite tuff occurs locally. Micaceous quartzite characterized by thin, schistose "pinstripe" partings is common in many areas.

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