Antietam and Harpers Formations, undivided

Includes, in descending order, the Antietam (CAa) and Harpers (CAh) Formations. Antietam Formation - gray, buff-weathering quartzite. Harpers Formation - Dark-greenish-gray phyllite and schist containing thin quartzite layers; includes Montalto Member (CAhm) - gray quartztite
State Pennsylvania
Name Antietam and Harpers Formations, undivided
Geologic age Cambrian
Lithologic constituents
Metamorphic > Metasedimentary > Metaclastic > Quartzite
Metamorphic > Schist
Metamorphic > Metasedimentary > Metaclastic > PhylliteHarpers Formation (CAh)
Comments Secondary unit description from USGS Geologic Names lexicon (ref. PA003): Antietam sandstone is a fine-grained white sandstone, 250 feet thick, with scolithus and Early Cambrian fossils. Underlies Cambrian limestone and overlies Harper's Ferry shales [Harpers shale]. Named for exposures east of Antietam Creek, in Harpers Ferry quad. [In southeastern PA, the lithologic character of the formation changes and it is there called Antietam quartzite in some areas and Antietam schist in other areas.]. 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.

Berg, T.M., Edmunds, W.E., Geyer, A.R., and others, compilers, 1980, Geologic map of Pennsylvania: Pennsylvania Geological Survey, 4th ser., Map 1, 2nd ed., 3 sheets, scale 1:250,000.

Pennsylvania Bureau of Topographic and Geologic Survey, Department of Conservation and Natural Resources, Miles, C.E., and Whitfield, T.G., compilers, 2001, Bedrock Geology of Pennsylvania, edition: 1.0, digital map, scale 1:250,000.

USGS Geologic Names lexicon found at:

NGMDB product
Counties Adams - Berks - Chester - Lancaster - Montgomery - York