Wissahickon Formation

Fine- to medium-grained biotite-quartz-plagioclase schist and gneiss that contains thin amphibolite layers. Schist and gneiss in alternating layers suggest a turbidite sequence of shale and graywacke. The rocks are at high metamorphic grade, and, in places, the more pelitic parts have partly melted forming veins of migmatite. Some exposures show evidence of polymetamorphism as micaceous minerals occur both within the schistosity and as static porphyroblasts.
State New Jersey
Name Wissahickon Formation
Geologic age Lower Cambrian and Late Proterozoic
Lithologic constituents
Major
Metamorphic > Gneiss > Biotite-gneissFine- to medium-grained biotite-quartz-plagioclase gneiss
Metamorphic > Schist > Amphibole-schistFine- to medium-grained biotite-quartz-plagioclase schist
Minor
Metamorphic > Amphibolite
Incidental
Metamorphic > MigmatiteThe rocks are at high metamorphic grade, and, in places, the more pelitic parts have partly melted forming veins of migmatite.
Comments Obducted rocks
References

Dalton, R.F., Herman, G.C., Monteverde, D.H., Pristas, R.S., Sugarman, P.J., and Volkert, R.A., 1999, New Jersey Department of Environmental Protection, Bedrock Geology and Topographic Base Maps of New Jersey: New Jersey Geological Survey CD Series CD 00-1; ARC/INFO (v. 7.1), scale 1:100,000.

Owens, James P., Sugarman, Peter J., Sohl, Norman F., Parker, Ronald A., Houghton, Hugh F., Volkert, Richard A., Drake, Avery A., Jr., and Orndorff, Randall C., 1998, Bedrock Geologic Map of Central and Southern New Jersey: U.S. Geological Survey Miscellaneous Investigations Series Map I-2540-B, 8 cross sections, 4 sheets, each size 58x41, scale 1:100,000.

https://pubs.er.usgs.gov/publication/i2540B

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