Geologic units in Lewis county, New York

Pulaski and Whetstone Gulf Formations (Upper Ordovician) at surface, covers 19 % of this area

Siltstone, shale.

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 14 % 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.

Oswego Sandstone (Upper Ordovician) at surface, covers 14 % of this area

Oswego Sandstone

Glacial and Alluvial Deposits (Quaternary) at surface, covers 11 % of this area

Underlying bedrock geology unknown.

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic) at surface, covers 8 % 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.

Trenton Group (Middle Ordovician) at surface, covers 7 % 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.

Mangerite, pyroxene-(hornblende) syenite gneiss (Middle Proterozoic) at surface, covers 4 % of this area

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

Hornblende-quartz syenite gneiss (Middle Proterozoic) at surface, covers 4 % of this area

Overprint signifies inequigranular texture.

Utica Shale (Middle Ordovician) at surface, covers 3 % of this area

Utica Shale

Leucogranitic (alaskitic) gneiss (Middle Proterozoic) at surface, covers 3 % 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.

Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic) at surface, covers 3 % of this area

Overprint signifies inequigranular texture.

Undifferentiated Medina Group and Queenston Formation (Upper Ordovician - Lower Silurian) at surface, covers 2 % of this area

Grimsby Formation-sandstones, shale; and Queenston Formation-siltstone, shale.

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.

Undivided metasedimentary rock and related migmatite (Middle Proterozoic) at surface, covers 1 % of this area

Undivided metasedimentary rock and related migmatite.

Hornblende syenite gneiss (Middle Proterozoic) at surface, covers 1 % of this area

Overprint signifies inequigranular texture.

Black River Group (Middle Ordovician) at surface, covers 1 % of this area

In Black River Valley: Chaumont Limestone-locally cherty; Lowville Limestone; Pamelia Formation-dolostone, shale, arkose. In Champlain Valley: Amsterdam, Isle La Motte, and Lowville Limestones: Pamelia Dolostone.

Undifferentiated Medina Group and Queenston Formation (Upper Ordovician - Lower Silurian) at surface, covers 1 % of this area

Grimsby Formation-sandstones, shale; and Queenston Formation-shale, siltstone.

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 0.9 % of this area

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

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers 0.9 % of this area

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

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 0.6 % 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. Overprint signifies inequigranular texture or phacoidal structure. In northwest Adirondacks, grades into Yphg.

Amphibolite (Middle Proterozoic) at surface, covers 0.5 % of this area

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

Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 0.3 % of this area

Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss.

Quartz-feldspar gneiss (Middle Proterozoic) at surface, covers 0.2 % of this area

With variable amounts of garnet, sillimanite, biotite.

Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock (Middle Proterozoic) at surface, covers 0.1 % 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).

Metanorthosite and anorthositic gneiss (Middle Proterozoic) at surface, covers < 0.1 % 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.

Potsdam Sandstone (Cambrian) at surface, covers < 0.1 % of this area

Potsdam Sandstone (Covey Hill in Quebec)

Theresa Formation (Cambrian - Lower Ordovician) at surface, covers < 0.1 % of this area

Dolostone, sandstone (Chateauguay in Quebec).