Geologic units in Essex county, New York

Metanorthosite and anorthositic gneiss (Middle Proterozoic) at surface, covers 47 % of this area

Mafic mineral percentage contoured in northwestern Marcy massif (St. Regis Quadrangle); contour value shown on high side of countoue line. See also Yach, Yack, Yamu.

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic) at surface, covers 12 % of this area

Variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.

Glacial and Alluvial Deposits (Quaternary) at surface, covers 7 % of this area

Underlying bedrock geology unknown.

Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic) at surface, covers 6 % of this area

Overprint signifies inequigranular texture.

Metagabbro (Middle Proterozoic) at surface, covers 3 % of this area

Metagabbro, olivine metagabbro, derived amphibolite.

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 3 % of this area

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.

Undivided metasedimentary rock and related migmatite (Middle Proterozoic) at surface, covers 3 % of this area

Undivided metasedimentary rock and related migmatite.

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers 3 % of this area

Predominantly; variably siliceous; in part with calcsilicate rock and amphibolite.

Beekmantown Group (in part) (Lower Ordovician) at surface, covers 2 % of this area

In St. Lawrence Valley: Ogdensburg Dolostone (Beauharnois Dolostone in Canada); In Champlain Valley: Providence Island Dolostone; Fort Cassin Formation-limestone, dolostone; Fort Ann Formation (Spellman of Clinton and Essex Counties)-limestone, dolostone; Cutting Formation-dolostone (locally cherty), limestone, siltstone. In Vermont: includes Bridport, Bascom, Cutting, and Shelburne carbonates.

Hybrid rock: anorthositic and metasedimentary rock (Middle Proterozoic) at surface, covers 2 % of this area

Ranges from anorthositic rock with local blocks, shreds or layers of undifferentiated metasediment, to mappable roof pendants and/or xenoliths of metasediment in anorthositic rock.

Leucogranitic (alaskitic) gneiss (Middle Proterozoic) at surface, covers 2 % of this area

Sodic plagioclase ranges from generally subordinate to locally dominant; locally with biotite, hornblende, pyroxene, garnet, sillimanite, disseminated magnetite; commonly contains metasedimentary layers, amphibolite, migmatite; plagioclase-rich variety is host to magnetite ore bodies in eastern Adirondacks.

Pyroxene and/or hornblende granitic gneiss (Middle Proterozoic) at surface, covers 2 % of this area

Biotitic in part; sodic plagioclase ranges from generally subordinate to locally dominant; plagioclase-rich facies locally contain disseminated magnetite and magnetite ore bodies; grades westward into Yhbg, and southward into Ylg.

Hybrid rock: mangeritic to charnockitic gneiss (Middle Proterozoic) at surface, covers 1 % of this area

With xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.

Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite (Middle Proterozoic) at surface, covers 1 % of this area

Locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.

Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock (Middle Proterozoic) at surface, covers 0.7 % of this area

Metasedimentary amphibolite, pyroxene granulite, and various gneisses; includes interlayered diopsidic and tremolitic marble and quartzite, and talc-tremolite rock (mined in Balmat-Edwards belt, northwest Adirondacks).

Potsdam Sandstone (Cambrian) at surface, covers 0.7 % of this area

Potsdam Sandstone (Covey Hill in Quebec)

Mangerite, pyroxene-(hornblende) syenite gneiss (Middle Proterozoic) at surface, covers 0.7 % of this area

Mangerite, pyroxene syenite gneiss - pyroxene-(hornblende) syenitic gneiss; mesoperthite common. Overprint signifies inequigranular texture.

Valcour, Crown Point, and Day Point Limestones (Middle Ordovician) at surface, covers 0.5 % of this area

Locally reefy, Ste. Therese Siltstone at base; Middlebury Limestone in Vermont; St. Martin and Rockcliffe Limestones in St. Lawrence Valley. Includes some Otbr and Obk adjacent to Champlain Thrust in Vermont.

Interlayered gabbroic or noritic metanorthosite (Middle Proterozoic) at surface, covers 0.4 % of this area

Mangerite or charnockite, and the Yach lithology.

Quartzite, quartz-biotite schist and graphitic schist (Middle Proterozoic) at surface, covers 0.4 % of this area

In part feldspathic, micaceous, garnetiferous, sillimanitic.

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 0.3 % of this area

Locally pyroxenic; commonly with subordinate leucogranitic gneiss, biotite-quartz-plagioclase gneiss, other metasedimentary rocks, amphibolite, migmatite. Amphibolite with porphyroblasts of K-feldspar locally prominent in northwest Adirondacks. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.

Trenton and Black River Groups, undivided (Middle Ordovician) at surface, covers 0.3 % of this area

Glens Falls and Orwell Limestones. In Canada: Lindsay, Verulam, Bodcaygeon, Gull River Limestones; Shadow Lake Dolostone.

Amphibolite (Middle Proterozoic) at surface, covers 0.2 % of this area

Commonly biotitic; garnetiferous, pyroxenic, in and adjacent to Adirondack Highlands.

Canajoharie Shale (Middle Ordovician) at surface, covers < 0.1 % of this area

Includes Hortonville and Ira Shales in Vermont.

Beekmantown Group (in part) (Cambrian) at surface, covers < 0.1 % of this area

In Champlain Valley: Whitehall Formation-dolostone, limestone (with Cryptozoon reefs); Ticonderoga Formation-dolostone (locally cherty), sandstone. In Vermont: Clarendon Springs Dolostone; Danby Formation-sandstone, quartzite, dolostone.

Stony Point Shale (Middle Ordovician) at surface, covers < 0.1 % of this area

Stony Point Shale

Lamprophyre, trachyte, and rhyolite dikes (Jurassic - Lower Cretaceous) at surface, covers < 0.1 % of this area

Lamprophyre, trachyte, and rhyolite dikes - not shown in Proterozoic terrane.

Trachyte porphyry (Jurassic - Lower Cretaceous) at surface, covers < 0.1 % of this area

Laccolith (?) at Cannon's Point near Willsboro, Essex County.

Gabbroic or noritic metanorthosite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Dark mineral content in excess of 10 percent (part of unit Ya).

Ferrohedenbergite-fayalite granite and granite gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Ferrohedenbergite-fayalite granite and granite gneiss.