Manhattan Formation (A Member)

Sillimanite-garnet-muscovite-biotite-quartz- plagioclase schists; calcite marble and calcsilicate rock at base.
State New York
Name Manhattan Formation (A Member)
Geologic age Middle Ordovician
Lithologic constituents
Metamorphic > Metasedimentary > Metacarbonate > Marblecalcite marble
Metamorphic > Metasedimentary > Calc-silicate-rock
Metamorphic > Schist > Mica-schistsillimanite-garnet-muscovite-biotite-quartz-plagioclase schists
Comments part of Trenton Group and Metamorphic Equivalents up to 8000 ft. (2400 m). This unit (Oma) is described under unit ?Om on printed map. Separated out, because it is used separately in digital map. Named it 'A Member' of Manhattan Formation. 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 Putnam - Rockland - Westchester