Geologic units in Saint Lawrence county, New York

Biotite and/or hornblende granite gneiss (Middle Proterozoic) at surface, covers 18 % 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 (in part) (Lower Ordovician) at surface, covers 16 % 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.

Theresa Formation (Cambrian - Lower Ordovician) at surface, covers 10 % of this area

Dolostone, sandstone (Chateauguay in Quebec).

Glacial and Alluvial Deposits (Quaternary) at surface, covers 9 % of this area

Underlying bedrock geology unknown.

Leucogranitic (alaskitic) gneiss (Middle Proterozoic) at surface, covers 8 % 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.

Calcitic and dolomitic marble (Middle Proterozoic) at surface, covers 8 % of this area

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

Potsdam Sandstone (Cambrian) at surface, covers 7 % of this area

Potsdam Sandstone (Covey Hill in Quebec)

Undivided metasedimentary rock and related migmatite (Middle Proterozoic) at surface, covers 5 % of this area

Undivided metasedimentary rock and related migmatite.

Biotite-quartz-plagioclase paragneiss, amphibolite, and related migmatite (Middle Proterozoic) at surface, covers 4 % of this area

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

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

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

Charnockite, granitic and quartz syenite gneiss (Middle Proterozoic) at surface, covers 2 % 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.

Dolomitic and calcitic marbles interlayered with significant amounts of calcsilicate rock (Middle Proterozoic) at surface, covers 2 % 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).

Mangerite, pyroxene-(hornblende) syenite gneiss (Middle Proterozoic) at surface, covers 2 % of this area

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

Amphibolite (Middle Proterozoic) at surface, covers 1 % of this area

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

Quartz-feldspar gneiss (Middle Proterozoic) at surface, covers 1.0 % of this area

With variable amounts of garnet, sillimanite, biotite.

Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss (Middle Proterozoic) at surface, covers 0.7 % of this area

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

Biotite-quartz-plagioclase paragneiss (Middle Proterozoic) at surface, covers 0.6 % of this area

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

Hornblende-quartz syenite gneiss (Middle Proterozoic) at surface, covers 0.6 % of this area

Overprint signifies inequigranular texture.

Charnockite, mangerite, pyroxene-quartz syenite gneiss (Middle Proterozoic) at surface, covers 0.5 % of this area

Overprint signifies inequigranular texture.

Ferrohedenbergite-fayalite granite and granite gneiss (Middle Proterozoic) at surface, covers 0.4 % of this area

Ferrohedenbergite-fayalite granite and granite gneiss.

Quartzite, quartz-biotite schist and graphitic schist (Middle Proterozoic) at surface, covers 0.3 % of this area

In part feldspathic, micaceous, garnetiferous, sillimanitic.

Valcour, Crown Point, and Day Point Limestones (Middle Ordovician) at surface, covers 0.2 % 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.

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.

Hornblende syenite gneiss (Middle Proterozoic) at surface, covers < 0.1 % of this area

Overprint signifies inequigranular texture.

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

Metagabbro, olivine metagabbro, derived amphibolite.

Trenton and Black River Groups, undivided (Middle Ordovician) at surface, covers < 0.1 % of this area

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