Wissahickon Formation; Metagraywacke

(Formerly mapped as Peters Creek Formation.) Rhythmically interbedded chlorite-muscovite meta-graywacke and fine-grained chlorite-muscovite schist; graded bedding locally preserved; thickness probably 2,000 to 3,000 feet.
State Maryland
Name Wissahickon Formation; Metagraywacke
Geologic age Late Precambrian (?)
Lithologic constituents
Metamorphic > Schist > Mica-schist > Muscovite-schist
Metamorphic > Metasedimentary > Metaclastic > Metasandstone > Metagraywacke
Stratigraphic units Wissahickon Formation; Glenarm Series

Cleaves, E.T., Edwards, J., Jr., and Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.

In 1995 the Water Resources Division of the U.S. Geological Survey digitized the geologic map of Maryland from the 1968 paper map (Reference MD001). Information about products from the Maryland Geological Survey can be found at http://www.mgs.md.gov/.

NGMDB product
Counties Cecil - Harford - Montgomery - Baltimore