Harrison/Ravenswood Gneiss

Harrison Gneiss - in New York and Connecticut, Brookfield diorite gneiss in Connecticut, and Ravenswood Gneiss in Brooklyn - biotite-hornblende-quartz-plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.
State New York
Name Harrison/Ravenswood Gneiss
Geologic age Ordovician?
Lithologic constituents
Metamorphic > Gneiss > Hornblende-gneissbiotite-hornblende-quartz-plagioclase gneiss with accessory garnet and sphene; plagioclase commonly occurs as augen.
Comments part of Eugeosynclinal (Allochthonous) Sequence up to 4000 ? ft. (1200 m). On printed map, unit has ? in front of Ohr. Second unit description and age change to Camrbrian to Early Ordovician from USGS Lexicon website (ref. NY046) and reference NY009: In New York City, Cameron's Line, a tectonic boundary which shows evidence of extreme compression and thrust faulting, separates the Manhattan Prong, with its Middle Proterozoic Fordham Gneiss overlain by Cambrian and Ordovician allochthonous units on the west, from the allochthonous eugeoclinal Hartland Formation and Ravenswood Granodiorite on the east. The Hartland is mapped in the east Bronx and Queens; the Ravenswood in is Queens, Kings, and lower east Manhattan. All three of these were previously mapped as Brooklyn Gneiss or Brooklyn Injection Gneiss, which should be abandoned. The age of the Hartland and Ravenswood is Cambrian and Ordovician, based on correlation with rocks of southwestern CT, their relative positions and lithologic similarities. Isotope data on the Ravenswood gives an early Paleozoic age, probably Early Ordovician (Baskerville and Mose, 1989).

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. and Mose, D.G., 1989, The separation of the Hartland Formation and Ravenswood Granodiorite from the Fordham Gneiss at Cameron's Line in the New York City area: Northeastern Geology, v. 11, no. 1, p. 22-28.

USGS Geologic Names lexicon found at: http://ngmdb.usgs.gov/Geolex/


NGMDB product
Counties New York - Queens - Westchester