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.
Potsdam Sandstone (Covey Hill in Quebec)
Interlayered amphibolite and granitic, charnockitic, mangeritic, or syenitic gneiss.
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.
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.
Dolostone, sandstone (Chateauguay in Quebec).
Mangerite, pyroxene syenite gneiss - pyroxene-(hornblende) syenitic gneiss; mesoperthite common. Overprint signifies inequigranular texture.
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.
Overprint signifies inequigranular texture.
Undivided metasedimentary rock and related migmatite.
Metagabbro, olivine metagabbro, derived amphibolite.
Interlayered metasedimentary rock and granitic, charnockitic, mangeritic, or syenitic gneiss.
Commonly biotitic; garnetiferous, pyroxenic, in and adjacent to Adirondack Highlands.
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.
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.
Predominantly; variably siliceous; in part with calcsilicate rock and amphibolite.