James Run Gneiss

Thick-bedded, light gray biotite-quartz-plagioclase gneiss with thin interbeds of quartz amphibolite; grades downward into sharply layered, thin- to thick-bedded paragneiss composed of subequal amounts of biotite-quartz-plagioclase gneiss and quartz amphibolite; thickness unknown.
State Maryland
Name James Run Gneiss
Geologic age Late Precambrian (?)
Lithologic constituents
Major
Metamorphic > Amphibolitequartz amphibolite
Metamorphic > Gneiss > Biotite-gneissincludes granitic gneiss and paragneiss
Metamorphic > Metasedimentary > Paragneiss
Comments secondary unit description from USGS Geologic Names Lexicon (ref MD004): Named for James Run, southeastern Harford Co., northeastern MD. Consists of interlayered quartz amphibolite and biotite-quartz-plagioclase gneiss. Conformably overlies garnet schist that closely resembles part of Wissahickon Formation, which in turn overlies microcline-mica gneiss similar to that of Setters Formation. Sequence is separated from main part of Glenarm metasedimentary rocks by broad belt of plutons across which correlation is uncertain. James Run Gneiss should not be included in Glenarm Series until further work can be done. Age is late Precambrian(?).
References

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/.

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

https://ngmdb.usgs.gov/Geolex/search

NGMDB product
Counties Baltimore - Harford