Chilhowee Group; 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
Lithologic constituents
Sedimentary > Clastic > Mudstone > Shale
Metamorphic > Metasedimentary > Metaclastic > Phyllite
Metamorphic > Metasedimentary > Metaclastic > Slate
Comments secondary unit description from USGS Geologic Names Lexicon (ref MD004): 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.
Stratigraphic units Chilhowee Group

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

USGS Geologic Names lexicon found at:

NGMDB product
Counties Carroll - Frederick - Washington