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.
Variably leucocratic, containing varying amounts of hornblende, pyroxenes, biotite; may contain interlayered amphibolite, metasedimentary gneiss, migmatite. Overprint signifies inequigranular texture or phacoidal structure.
Underlying bedrock geology unknown.
Overprint signifies inequigranular texture.
Metagabbro, olivine metagabbro, derived amphibolite.
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.
Undivided metasedimentary rock and related migmatite.
Predominantly; variably siliceous; in part with calcsilicate rock and amphibolite.
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.
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.
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.
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.
With xenocrysts of calcic andesine and, locally, xenoliths of anorthosite; with increasing percentage of anorthosite component, passes gradationally into anorthositic rocks.
Locally sillimanitic; commonly garnetiferous in and adjacent to Adirondack Highlands.
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 (Covey Hill in Quebec)
Mangerite, pyroxene syenite gneiss - pyroxene-(hornblende) syenitic gneiss; mesoperthite common. Overprint signifies inequigranular texture.
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.
Mangerite or charnockite, and the Yach lithology.
In part feldspathic, micaceous, garnetiferous, sillimanitic.
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.
Glens Falls and Orwell Limestones. In Canada: Lindsay, Verulam, Bodcaygeon, Gull River Limestones; Shadow Lake Dolostone.
Commonly biotitic; garnetiferous, pyroxenic, in and adjacent to Adirondack Highlands.
Includes Hortonville and Ira Shales in Vermont.
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
Lamprophyre, trachyte, and rhyolite dikes - not shown in Proterozoic terrane.
Laccolith (?) at Cannon's Point near Willsboro, Essex County.
Dark mineral content in excess of 10 percent (part of unit Ya).
Ferrohedenbergite-fayalite granite and granite gneiss.