{{Infobox rockunit , name = Conococheague Formation , image = Conococheague1.jpg , caption = Etched section of rock from the Conococheague Formation from

Washington County, Maryland Washington County is located in the western part of the U.S. state of Maryland. As of the 2020 census, the population was 154,705. Its county seat is Hagerstown. Washington County was the first county in the United States to be named for the ...

(dolomite is lighter than the limestone) , type = sedimentary , prilithology =

Limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

, otherlithology =

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 ...

, sandstone , namedfor =

Conococheague Creek Conococheague Creek, a tributary of the Potomac River, is a free-flowing stream that originates in Pennsylvania and empties into the Potomac River near Williamsport, Maryland. It is in length,U.S. Geological Survey. National Hydrography Dataset h ...

Stose, G.W., 1908, The Cambro-Ordovician limestones of the Appalachian Valley in southern Pennsylvania:

Journal of Geology ''The Journal of Geology'' publishes research on geology, geophysics, geochemistry, sedimentology, geomorphology, petrology, plate tectonics, volcanology, structural geology, mineralogy, and planetary sciences. Its content ranges from planetary evo ...

, v. 16, p. 698-714. , namedby = G. W. Stose, 1908 , region =

Appalachian Basin The geology of the Appalachians dates back to more than 480 million years ago. A look at rocks exposed in today's Appalachian Mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ...

of eastern

North America North America is a continent in the Northern Hemisphere and almost entirely within the Western Hemisphere. It is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South America and the Car ...

, unitof = , subunits = Big Spring Station Member , overlies = Elbrook Formation , underlies = Beekmantown Dolomite , thickness = , extent = Maryland, Pennsylvania, Virginia, West Virginia , age =

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 = Cambrian The Conococheague Formation is a mapped Appalachian bedrock unit of

age, consisting primarily of

limestone Limestone ( calcium carbonate ) is a type of carbonate sedimentary rock which is the main source of the material lime. It is composed mostly of the minerals calcite and aragonite, which are different crystal forms of . Limestone forms whe ...

and

. It occurs in central

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 ...

, southern and central

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, ...

, the Valley and Ridge of

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 easternmost

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 B ...

Description

Depositional environment

The

depositional environment In geology, depositional environment or sedimentary environment describes the combination of physical, chemical, and biological processes associated with the deposition of a particular type of sediment and, therefore, the rock types that will be ...

of the Conococheague was most likely shallow marine to tidal on a carbonate platform.

Notable Exposures

The type section is located at

Scotland Scotland (, ) is a country that is part of the United Kingdom. Covering the northern third of the island of Great Britain, mainland Scotland has a border with England to the southeast and is otherwise surrounded by the Atlantic Ocean to the ...

Franklin County, Pennsylvania Franklin County is a county in the Commonwealth of Pennsylvania. As of the 2020 census, the population was 155,932 Its county seat is Chambersburg. Franklin County comprises the Chambersburg–Waynesboro, PA Metropolitan Statistical Area, whi ...

(northeast of

Chambersburg Chambersburg is a borough in and the county seat of Franklin County, in the South Central region of Pennsylvania, United States. It is in the Cumberland Valley, which is part of the Great Appalachian Valley, and north of Maryland and the Mas ...

). Accessible outcrops occur along various roadcuts and waterways in the area, including roadcuts near mile marker 20 of

I-70 Interstate 70 (I-70) is a major east–west Interstate Highway in the United States that runs from I-15 near Cove Fort, Utah, to a park and ride lot just east of I-695 in Baltimore, Maryland, and is the fifth-longest Interstate in the c ...

near Hagerstown, Maryland. The

bedding Bedding, also known as bedclothes or bed linen, is the materials laid above the mattress of a bed for hygiene, warmth, protection of the mattress, and decorative effect. Bedding is the removable and washable portion of a human sleeping environm ...

at this site is nearly vertical, with the strike nearly perpendicular to the highway, and thus one can easily walk up and down the sections. The Conococheague also forms dramatic, 100- foot cliffs along 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 ...

upstream of

Shepherdstown, West Virginia Shepherdstown is a town in Jefferson County, West Virginia, United States, located in the lower Shenandoah Valley along the Potomac River. Home to Shepherd University, the town's population was 1,734 at the time of the 2010 census. History 18 ...

(northwest of

Harpers Ferry 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 ...

), where entrenched

meander A meander is one of a series of regular sinuous curves in the channel of a river or other watercourse. It is produced as a watercourse erodes the sediments of an outer, concave bank ( cut bank) and deposits sediments on an inner, convex ba ...

s expose mile-long sections of tilted Conococheague strata. These may be easily seen from the towpath trail of the

Chesapeake and Ohio Canal National Historical Park The Chesapeake and Ohio Canal National Historical Park is located in the District of Columbia and the state of Maryland. The park was established in 1961 as a National Monument by President Dwight D. Eisenhower to preserve the neglected remains o ...

along the Maryland bank of the Potomac. In Shepherdstown itself, the top of a Conococheague cliff provides the setting for the monument to

steamboat A steamboat is a boat that is marine propulsion, propelled primarily by marine steam engine, steam power, typically driving propellers or Paddle steamer, paddlewheels. Steamboats sometimes use the ship prefix, prefix designation SS, S.S. or S/S ...

-inventor

James Rumsey James Rumsey (1743 – December 21, 1792) was an American mechanical engineer chiefly known for exhibiting a boat propelled by machinery in 1787 on the Potomac River at Shepherdstown in present-day West Virginia before a crowd of local notables ...

Fossils

Conodonts are present in the Conococheague.

Thrombolite Thrombolites (from Ancient Greek θρόμβος ''thrómbos'' meaning " clot" and λῐ́θος ''líthos'' meaning "stone") are clotted accretionary structures formed in shallow water by the trapping, binding, and cementation of sedimentary g ...

s and the possible chiton '' Matthevia'' are present in the Boxley Blue Ridge Quarry in Bedford County, Virginia.Unusual Cambrian Thrombolites from the Boxley Blue Ridge Quarry, Bedford County, Virginia
by A. C. Dooley, Jr., JEFFERSONIANA, Number 19, 10 January 2009, Virginia Museum of Natural History

Age

Relative-age dating of the Conococheague places it in the Upper

period.

References

Generalized Stratigraphic Column for West Virginia
Cambrian United States Dolomite formations Limestone formations of the United States Cambrian geology of Pennsylvania Cambrian Maryland Cambrian geology of Virginia Cambrian West Virginia Cambrian System of North America Cambrian southern paleotemperate deposits