Manhattan Formation, undivided

Pelitic schists, amphibolite; Units ?Omb, ?Omc, and ?Omd may be Cambrian eugeosynclinal rocks thrust upon Oma; ?Omd - sillimanite-garnet-muscovite-biotite-plagioclase-quartz gneiss; ?Omc - sillimanite-garnet-muscovite-biotite-quartz-plagioclase schistose gneiss, sillimanite nodules, local quartz-rich layers; ?Omb - discontinous unit of amphibolite and ?Omc-type schist.
State New York
Name Manhattan Formation, undivided
Geologic age Ordovician?
Lithologic constituents
Metamorphic > Amphibolite
Metamorphic > Gneisssillimanite-garnet-muscovite-biotite-plagioclase-quartz gneiss; sillimanite-garnet-muscovite-biotite-quartz-plagioclase schistose gneiss
Metamorphic > Schist > Pelitic-schist
Comments part of Trenton Group and Metamorphic Equivalents up to 8000 ft. (2400 m). All units (?Omb - ?Omd) are mapped under Om in digital map. Only unit Oma is separated out, so I separated it out of this description. Unit is also mentioned under Eugeosynclinal (Allochthonous) Sequence; uses same symbol and color. Age change and second unit description from USGS Lexicon website (ref. NY046) and reference NY004: Manhattan Schist member A replaced by Walloomsac Formation (not new) based on work by Jackson and Hall (1982), Hall (in press), and A.A. Drake (1990, pers. commun.). In addition, L.M. Hall (1985?, pers. commun.) determined that member B of the Manhattan Schist is part of member C and thus recommended the abandonment of member B (Baskerville, 1992) .

Fisher, D.W., Isachsen, Y.W., and Rickard, L.V., 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson, New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250,000.

Baskerville, C.A., 1992, Bedrock and engineering geologic maps of Bronx County and parts of New York and Queens Counties, New York: U.S. Geological Survey Miscellaneous Investigations Series Map, I-2003, 2 sheets, scale 1:24,000.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Bronx - Dutchess - New York - Putnam - Westchester