{{Infobox rockunit
, name = Conococheague Formation
, image = Conococheague1.jpg
, caption = Etched section of rock from the Conococheague Formation from
Washington County, Maryland
Washington County is a County (United States), county located in the U.S. state of Maryland. The population was 154,705 as of the 2020 United States census, 2020 census. Its county seat and largest city is Hagerstown, Maryland, Hagerstown. The ...
(dolomite is lighter than the limestone)
, type = sedimentary
, prilithology =
Limestone
Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
, otherlithology = dolomite, sandstone
, namedfor = Conococheague CreekStose, 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 ev ...
, v. 16, p. 698-714.
, namedby = G. W. Stose, 1908
, region =
Appalachian Basin
The geology of the Appalachians dates back more than 1.2 billion years to the Mesoproterozoic era when two continental cratons collided to form the supercontinent Rodinia, 500 million years prior to the development of the range during the form ...
of eastern
North America
North America is a continent in the Northern Hemisphere, Northern and Western Hemisphere, Western hemispheres. North America is bordered to the north by the Arctic Ocean, to the east by the Atlantic Ocean, to the southeast by South Ameri ...
, unitof =
, subunits = Big Spring Station Member
, overlies = Elbrook Formation
, underlies = Beekmantown Dolomite
, thickness =
, extent = Maryland, Pennsylvania, Virginia, West Virginia
, age =
Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
, period = Cambrian
The Conococheague Formation is a mapped
Appalachia
Appalachia ( ) is a geographic region located in the Appalachian Mountains#Regions, central and southern sections of the Appalachian Mountains in the east of North America. In the north, its boundaries stretch from the western Catskill Mountai ...
n bedrock unit of
Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...
age, consisting primarily of
limestone
Limestone is a type of carbonate rock, carbonate sedimentary rock which is the main source of the material Lime (material), lime. It is composed mostly of the minerals calcite and aragonite, which are different Polymorphism (materials science) ...
Maryland
Maryland ( ) is a U.S. state, state in the Mid-Atlantic (United States), Mid-Atlantic region of the United States. It borders the states of Virginia to its south, West Virginia to its west, Pennsylvania to its north, and Delaware to its east ...
, southern and central
Pennsylvania
Pennsylvania, officially the Commonwealth of Pennsylvania, is a U.S. state, state spanning the Mid-Atlantic (United States), Mid-Atlantic, Northeastern United States, Northeastern, Appalachian, and Great Lakes region, Great Lakes regions o ...
, the Valley and Ridge of
Virginia
Virginia, officially the Commonwealth of Virginia, is a U.S. state, state in the Southeastern United States, Southeastern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States between the East Coast of the United States ...
and easternmost
West Virginia
West Virginia is a mountainous U.S. state, state in the Southern United States, Southern and Mid-Atlantic (United States), Mid-Atlantic regions of the United States.The United States Census Bureau, Census Bureau and the Association of American ...
.
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 b ...
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 Countries of the United Kingdom, country that is part of the United Kingdom. It contains nearly one-third of the United Kingdom's land area, consisting of the northern part of the island of Great Britain and more than 790 adjac ...
in Franklin County, Pennsylvania (northeast of Chambersburg).
Accessible outcrops occur along various roadcuts and waterways in the area, including roadcuts near mile marker 20 of I-70 near Hagerstown, Maryland. The
bedding
Bedding, also called 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 environment ...
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
The foot (: feet) is an anatomical structure found in many vertebrates. It is the terminal portion of a limb which bears weight and allows locomotion. In many animals with feet, the foot is an organ at the terminal part of the leg made up o ...
cliffs along the
Potomac River
The Potomac River () is in the Mid-Atlantic (United States), Mid-Atlantic region of the United States and flows from the Potomac Highlands in West Virginia to Chesapeake Bay in Maryland. It is long,U.S. Geological Survey. National Hydrography D ...
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 1,531 at the time of the 2020 census. The town wa ...
(northwest of
Harpers Ferry
Harpers Ferry is a historic town in Jefferson County, West Virginia, United States. The population was 269 at the 2020 United States census. Situated at the confluence of the Potomac River, Potomac and Shenandoah River, Shenandoah Rivers in the ...
), where entrenched
meander
A meander is one of a series of regular sinuous curves in the Channel (geography), channel of a river or other watercourse. It is produced as a watercourse erosion, erodes the sediments of an outer, concave bank (cut bank, cut bank or river cl ...
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 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. The term ''steamboat'' is used to refer to small steam-powered vessels worki ...
-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
Conodont
Conodonts, are an extinct group of marine jawless vertebrates belonging to the class Conodonta (from Ancient Greek κῶνος (''kōnos''), meaning " cone", and ὀδούς (''odoús''), meaning "tooth"). They are primarily known from their hard ...
s are present in the Conococheague.
Thrombolites and the possible
chiton
Chitons () are marine molluscs of varying size in the class Polyplacophora ( ), formerly known as Amphineura. About 940 extant and 430 fossil species are recognized.
They are also sometimes known as sea cradles or coat-of-mail shells or suck ...
Relative-age dating of the Conococheague places it in the Upper
Cambrian
The Cambrian ( ) is the first geological period of the Paleozoic Era, and the Phanerozoic Eon. The Cambrian lasted 51.95 million years from the end of the preceding Ediacaran period 538.8 Ma (million years ago) to the beginning of the Ordov ...