Geologic units in Herkimer county, New York

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 16 % 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.

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 12 % of this area

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

Utica Shale (Middle Ordovician) at surface, covers 8 % of this area

Utica Shale

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

Underlying bedrock geology unknown.

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 6 % 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. In northwest Adirondacks, grades into Yphg.

Undivided metasedimentary rock and related migmatite (Middle Proterozoic) at surface, covers 6 % of this area

Undivided metasedimentary rock and related migmatite.

Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic) at surface, covers 5 % of this area

Overprint signifies inequigranular texture.

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic) at surface, covers 4 % 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.

Frankfort Formation (Upper Ordovician) at surface, covers 4 % of this area

Shale, siltstone.

Helderberg Group (Lower Devonian) at surface, covers 4 % of this area

West of Albany: Alsen, Becraft, New Scotland, Kalkberg, Coeymans, and Manlius Limestones; Rondout Dolostone. South of Albany: Port Ewen, Alsen thru Manlius Limestones; Rondout Dolostone.

Utica Shale (Middle Ordovician) at surface, covers 4 % of this area

Utica Shale

Trenton and Black River Groups, undivided (Middle Ordovician) at surface, covers 4 % of this area

Mohawk Valley: Dolgeville, Denley, Sugar River, Kings Falls, Glens Falls, Rockland, Amsterdam, and Lowville Limestones. Washington County: Glens Falls and Orwell Limestones.

Onondaga Limestone (Lower to Middle Devonian) at surface, covers 3 % of this area

Schoharie Formation-shale, limestone; Carlisle Center Siltstone; Esopus Shale.

Trenton Group (Middle Ordovician) at surface, covers 2 % of this area

In Black River Valley: Cobourg Formation-Hillier shale and limestone Member, Hallowell limestone Member; Denley, Sugar River, Kings Falls, and Rockland Limestones. In Champlain Valley: Glens Falls Formation-Montreal shale and limestone Member, Larrabee limestone Member.

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 2 % of this area

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

Cobleskill Limestone (Upper Silurian) at surface, covers 2 % of this area

Bertie, Camillus, and Syracuse Formations - shale, dolostone; Brayman Shale.

Biotite-quartz-plagioclase gneiss (Middle Proterozoic) at surface, covers 2 % of this area

Commonly very low in biotite content, with interbedded feldspathic and biotitic quartzite and amphibolite; sillimanite and garnet common, graphite sporadic.

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 1 % 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.

Beekmantown Group (Cambrian) at surface, covers 1 % of this area

Mohawk Valley: Little Falls Dolostone-chert; Hoyt Formation-limestone, dolostone, oolite. Washington county: Whitehall Formation-dolostone, limestone; Ticonderoga Dolostone-chert.

Clinton Group (Silurian) at surface, covers 1 % of this area

Herkimer Sandstone including Joslin Hill and Jordanville Members; Kirkland Hematite; Willowvale Shale; Westmoreland Hematite; Sauquoit Formation-sandstone, shale; Otsquago Sandstone; Oneida Conglomerate.

Undivided metasedimentary rock and related migmatite (Middle Proterozoic) at surface, covers 0.8 % of this area

Undivided metasedimentary rock and related migmatite.

Quartz-feldspar gneiss (Middle Proterozoic) at surface, covers 0.8 % of this area

With variable amounts of garnet, sillimanite, biotite.

Marcellus Formation (Middle Devonian) at surface, covers 0.7 % of this area

Pecksport, Solsville, Otsego, and Chittenango shale and sandstone Members, Cherry Valley Limestone, and Union Springs Shale Members.

Vernon Shale (Upper Silurian) at surface, covers 0.7 % of this area

Vernon Shale

Pyroxene-hornblende-quartz-plagioclase gneiss (Middle Proterozoic) at surface, covers 0.6 % of this area

Pyroxene-hornblende-quartz-plagioclase gneiss.

Glacial and Alluvial Deposits (Quaternary) at surface, covers 0.6 % of this area

Underlying bedrock geology unknown.

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers 0.2 % of this area

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

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 0.2 % 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.

Beekmantown Group (Lower Ordovician) at surface, covers 0.2 % of this area

Mohawk Valley: Chuctanunda Creek Dolostone; Tribes Hill Formation-limestone, dolostaone; Gailor Dolostone. Washington County: Providence Island Dolostone; Fort Cassin Formation-limestone, dolostone; Fort Ann Formation-limestone, dolostone; Cutting Formation-dolostone, local chert, limestone at top, siltstone at base.

Ilion Shale (Upper Silurian) at surface, covers 0.2 % of this area

Ilion Shale

Black River Group (Middle Ordovician) at surface, covers 0.1 % of this area

Chaumont Limestone-chert; Lowville Limestone; Pamelia Dolostone.

Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic) at surface, covers 0.1 % of this area

Overprint signifies inequigranular texture.

Leucogranitic (alaskitic) gneiss (Middle Proterozoic) at surface, covers 0.1 % 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.

Undifferentiated Hamilton Group (Middle Devonian) at surface, covers < 0.1 % of this area

Shale, siltstone. In eastern Orange County: Skunnemunk Formation-sandstone, conglomerate; Bellvale Formation-shale, sandstone; Cornwall Shale.

Amphibolite (Middle Proterozoic) at surface, covers < 0.1 % of this area

Commonly biotitic; garnetiferous, pyroxenic, in and adjacent to central massif of Adirondacks.

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers < 0.1 % of this area

Variably siliceous; in part with calcsilicate rock and amphibolite.

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).