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Chilhowee Group; Harpers Formation

Harpers Formation - Brown to dark bluish-gray banded shale, to light bluish-gray, finely laminated phyllite; distinctively pale purple in basal part; bedding obscured by cleavage; increasingly metamorphosed toward east from shale to slate and phyllite; estimated thickness 2,000 feet.
State Maryland
Name Chilhowee Group; Harpers Formation
Geologic age Cambrian
Comments secondary unit description from USGS Geologic Names lexicon (ref MD005): The Harpers Formation is predominantly a dark-greenish-gray to brownish-gray, very fine-grained, laminated to massively bedded, phyllitic metasiltstone. The base of the unit is locally sharp, but is transitional with the underlying quartz-pebble conglomeratic quartzite of the upper member of the Weverton Formation. The metasiltstone is highly cleaved and bedding is obscure. Thickness of the Harpers in the mapped area is 732 meters. The Harpers Formation overlies the Weverton Formation and underlies the Antietam Quartzite. The unit is of Early Cambrian age.
Primary rock type shale
Secondary rock type phyllite
Other rock types slate
Lithologic constituents
Major
Sedimentary > Clastic > Mudstone > Shale
Metamorphic > Metasedimentary > Metaclastic > Phyllite
Minor
Metamorphic > Metasedimentary > Metaclastic > Slate
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Unpublished digital version of the Maryland state geologic map that was digitized by the USGS Water Resources Office in Towson, MD
USGS Geologic Names Lexicon (GEOLEX)
Counties Carroll - Frederick - Washington