James Run Gneiss (MDjg;4)

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	NGMDB product page for 16548
Counties	Baltimore - Harford

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

NGMDB product page for 16548

Counties

Baltimore - Harford