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Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation

Potomac Group - Interbedded quartzose gravels; protoquartzitic to orthoquartzitic argillaceous sands; and white, dark gray, and multicolored silts and clays; thickness 0 to 800 feet. Includes Raritan and Patapsco Formations - Gray, brown, and red variegated silts and clays; lenticular, cross-bedded, argillaceous, subrounded sands; minor gravels; thickness 0 to 400 feet; Arundel Clay - Dark gray and maroon lignitic clays; abundant siderite concretions; present only in Baltimore-Washington area; thickness 0 to 100 feet; and Patuxent Formation - White or light gray to orange-brown, moderately sorted, cross-bedded, argillaceous, angular sands and subrounded quartz gravels; silts and clays subordinate, predominantly pale gray; thickness 0 to 250 feet.
State Maryland
Name Potomac Group, including Raritan and Patapsco Formations, Arundel Clay, and Patuxent Formation
Geologic age Cretaceous
Primary rock type gravel
Secondary rock type sand
Other rock types silt; clay or mud
Lithologic constituents
Major
Unconsolidated > Coarse-detrital > Sand
Minor
Unconsolidated > Coarse-detrital > Gravel
Unconsolidated > Fine-detrital > Silt
Unconsolidated > Fine-detrital > Clay
Map references
Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.
Unit references
Cleaves, E.T., Edwards, J., Jr., Glaser, J.D., 1968, Geologic Map of Maryland: Maryland Geological Survey, Baltimore, Maryland, scale 1:250,000.
Unpublished digital version of the Maryland state geologic map that was digitized by the USGS Water Resources Office in Towson, MD
Counties Anne Arundel - Baltimore - Cecil - Charles - Harford - Howard - Kent - Montgomery - Prince George's - Baltimore