Bulletin 799 Plate 2A Harpers Schist photomicrograph

The Harpers Formation is a

geologic formation A geological formation, or simply formation, is a body of rock having a consistent set of physical characteristics ( lithology) that distinguishes it from adjacent bodies of rock, and which occupies a particular position in the layers of rock exp ...

Maryland Maryland ( ) is a state in the Mid-Atlantic region of the United States. It shares borders with Virginia, West Virginia, and the District of Columbia to its south and west; Pennsylvania to its north; and Delaware and the Atlantic Ocean to ...

Pennsylvania Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...

Virginia Virginia, officially the Commonwealth of Virginia, is a state in the Mid-Atlantic and Southeastern regions of the United States, between the Atlantic Coast and the Appalachian Mountains. The geography and climate of the Commonwealth ar ...

, and

West Virginia West Virginia is a state in the Appalachian, Mid-Atlantic and Southeastern regions of the United States.The Census Bureau and the Association of American Geographers classify West Virginia as part of the Southern United States while the Bur ...

, consisting of

schist Schist ( ) is a medium-grained metamorphic rock showing pronounced schistosity. This means that the rock is composed of mineral grains easily seen with a low-power hand lens, oriented in such a way that the rock is easily split into thin flakes o ...

phyllite Phyllite ( ) is a type of foliated metamorphic rock created from slate that is further metamorphosed so that very fine grained white mica achieves a preferred orientation.Stephen Marshak ''Essentials of Geology'', 3rd ed. It is primarily compo ...

, and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of clay minerals (hydrous aluminium phyllosilicates, e.g. kaolin, Al2 Si2 O5( OH)4) and tiny fragments (silt-sized particles) of other minerals, especial ...

. It dates back to the early

Cambrian The Cambrian Period ( ; sometimes symbolized C with bar, Ꞓ) was the first geological period of the Paleozoic Era, and of the Phanerozoic Eon. The Cambrian lasted 53.4 million years from the end of the preceding Ediacaran Period 538.8 million ...

period Period may refer to: Common uses * Era, a length or span of time * Full stop (or period), a punctuation mark Arts, entertainment, and media * Period (music), a concept in musical composition * Periodic sentence (or rhetorical period), a concept ...

. It is considered part of the

Chilhowee Group The Chilhowee Group is a sedimentary body composed of early Cambrian siliciclastic sedimentary rocks which crop out along the eastern margin of the Blue Ridge province in Alabama, Maryland, Tennessee, North Carolina, Virginia, and West Virginia. ...

Notable exposures

The type section is in gorges of the

Potomac River The Potomac River () drains the Mid-Atlantic United States, flowing from the Potomac Highlands into Chesapeake Bay. It is long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map. Retrieved Augus ...

and the

Shenandoah River The Shenandoah River is the principal tributary of the Potomac River, long with two forks approximately long each,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map accessed August 15, 2011 in t ...

Harpers Ferry, West Virginia Harpers Ferry is a historic town in Jefferson County, West Virginia. It is located in the lower Shenandoah Valley. The population was 285 at the 2020 census. Situated at the confluence of the Potomac and Shenandoah rivers, where the U.S. stat ...

. The Harpers Formation overlies the Ledger Formation (

dolomite Dolomite may refer to: *Dolomite (mineral), a carbonate mineral *Dolomite (rock), also known as dolostone, a sedimentary carbonate rock *Dolomite, Alabama, United States, an unincorporated community *Dolomite, California, United States, an unincor ...

) due to a

thrust fault A thrust fault is a break in the Earth's crust, across which older rocks are pushed above younger rocks. Thrust geometry and nomenclature Reverse faults A thrust fault is a type of reverse fault that has a dip of 45 degrees or less. If ...

in small roadside quarry (currently overgrown) on Pottery Hill, southwest of

York, Pennsylvania York ( Pennsylvania Dutch: ''Yarrick''), known as the White Rose City (after the symbol of the House of York), is the county seat of York County, Pennsylvania, United States. It is located in the south-central region of the state. The populati ...

. A. J. Stose and G. W. Stose, 1944. ''Geology of the Hanover-York district'', U. S. Geological Survey Professional paper 204.

Gallery

File:Quartzite (Harpers Formation, Lower Cambrian; Verona, Virginia, USA).jpg, Quartzite sample of Harpers Formation from near

Verona, Virginia Verona is a census-designated place (CDP) in Augusta County, Virginia, United States. The population was 4,239 at the 2010 census. It is part of the Staunton– Waynesboro Micropolitan Statistical Area. History Mount Airy and Verona School ...

File:Jefferson Rock, Harpers Ferry, WV - area view.jpg, Harpers Shale by

Jefferson Rock Jefferson Rock is a rock formation on the Appalachian Trail in Harpers Ferry, West Virginia. It consists of several large masses of Harpers shale, piled one upon the other, that overlook the Shenandoah River just prior to its confluence with the P ...

Harpers Phyllite Pottery Hill outcrop 2022.jpg, Sample of phyllite from the outcrop at Pottery Hill, southwest of

York York is a cathedral city with Roman origins, sited at the confluence of the rivers Ouse and Foss in North Yorkshire, England. It is the historic county town of Yorkshire. The city has many historic buildings and other structures, such as a ...

References

Cambrian West Virginia {{Cambrian-stub