The

Silurian The Silurian ( ) is a geologic period and system spanning 23.5 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the third and shortest period of t ...

Tuscarora Formation — also known as Tuscarora Sandstone or Tuscarora Quartzite — is a mapped

bedrock In geology, bedrock is solid rock that lies under loose material ( regolith) within the crust of Earth or another terrestrial planet. Definition Bedrock is the solid rock that underlies looser surface material. An exposed portion of bed ...

unit in

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 ...

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 ...

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 ...

, and

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 ...

, US.

Description

The Tuscarora is a thin- to thick-bedded fine-grained to coarse-grained orthoquartzite. It is a white to medium-gray or gray-green subgraywacke,

sandstone Sandstone is a Clastic rock#Sedimentary clastic rocks, clastic sedimentary rock composed mainly of grain size, sand-sized (0.0625 to 2 mm) silicate mineral, silicate grains, Cementation (geology), cemented together by another mineral. Sand ...

siltstone Siltstone, also known as aleurolite, is a clastic sedimentary rock that is composed mostly of silt. It is a form of mudrock with a low clay mineral content, which can be distinguished from shale by its lack of fissility. Although its permeabil ...

and

shale Shale is a fine-grained, clastic sedimentary rock formed from mud that is a mix of flakes of Clay mineral, clay minerals (hydrous aluminium phyllosilicates, e.g., Kaolinite, kaolin, aluminium, Al2Silicon, Si2Oxygen, O5(hydroxide, OH)4) and tiny f ...

, cross-stratified and conglomeratic conglomerate in parts, containing a few

interbeds.Berg, T.M., Edmunds, W.E., Geyer, A.R. and others, compilers, (1980). Geologic Map of Pennsylvania: Pennsylvania Geologic Survey, Map 1, scale 1:250,000. Details of the type locality and of stratigraphic nomenclature for this unit as used by the U.S. Geological Survey are available on-line at the National Geologic Map Database. The Tuscarora and its lateral equivalents are the primary ridge-formers of the

Ridge-and-Valley Appalachians The Ridge-and-Valley Appalachians, also called the Ridge and Valley Province or the Valley and Ridge Appalachians, are a physiographic province of the larger Appalachian Highlands division. The physiographic province is divided into three se ...

in the eastern

United States The United States of America (USA), also known as the United States (U.S.) or America, is a country primarily located in North America. It is a federal republic of 50 U.S. state, states and a federal capital district, Washington, D.C. The 48 ...

It is typically 935 feet thick in Pennsylvania, and in Maryland varies from 60 feet to 400 feet thick from east to west.

Notable exposures

The Tuscarora Formation is commonly exposed on various ridge crests and in many water gaps in the Ridge and Valley

physiographic province physiographic province is a geographic region with a characteristic geomorphology, and often specific subsurface rock type or structural elements. The continents are subdivided into various physiographic provinces, each having a specific characte ...

of the Appalachians of Pennsylvania, Maryland, and West Virginia, particularly along the Wills Mountain Anticline. In Pennsylvania, the Tuscarora is exposed along US 30 on the north and south sides of the Narrows in central Bedford County, where it is nearly vertical. It is also well-exposed in the core of Jack's Mountain in Jack's Narrows, where the

Juniata River The Juniata River () is a tributary of the Susquehanna River, approximately long,U.S. Geological Survey. National Hydrography Dataset high-resolution flowline dataThe National Map , accessed August 8, 2011 in central Pennsylvania. The river is ...

cuts through the mountain, just west of Mount Union. The Standing Stone Trail traverses this cut, and many of the "Thousand Steps" here are Tuscarora quartzite. In Maryland, the

National Road The National Road (also known as the Cumberland Road) was the first major improved highway in the United States built by the federal government. Built between 1811 and 1837, the road connected the Potomac and Ohio Rivers and was a main tran ...

( US 40) passes arched Tuscarora sandstone outcrops in the Cumberland Narrows in Allegany County. In West Virginia, the River Knobs along the North Fork of the South Branch of the Potomac River in Pendleton County include dramatic outcrops of nearly vertical Tuscarora sandstone. Some of the better known of these exposures are

Seneca Rocks Seneca Rocks is a large cliff, crag and local landmark in Pendleton County, West Virginia, Pendleton County in the Eastern Panhandle of West Virginia, United States. The south peak is the only peak inaccessible except by technical rock climbing ...

, Champe Rocks, Judy Rocks, and Nelson Rocks. These cliffs are clearly visible along U.S. Route 33 and West Virginia Routes 28 and 55. North Fork Mountain, to the east of the River Knobs, is a long Ridge and Valley

anticline In structural geology, an anticline is a type of Fold (geology), fold that is an arch-like shape and has its oldest Bed (geology), beds at its core, whereas a syncline is the inverse of an anticline. A typical anticline is convex curve, c ...

ridge capped by Tuscarora sandstone. Two of the more comprehensive exposures of the Tuscarora Formation are in two quarries at the crest and south end of Canoe Mountain
Spruce Creek Quadrangle
.

Geographic Extent

The Tuscarora is present in

, and

, US.

Stratigraphic Setting

The Tuscarora rests conformably atop the Juniata Formation and conformably below the Clinton Group in

. The Tuscarora is a lateral equivalent of the Minsi and Weiders members of the Shawangunk Formation in eastern

New Jersey New Jersey is a U.S. state, state located in both the Mid-Atlantic States, Mid-Atlantic and Northeastern United States, Northeastern regions of the United States. Located at the geographic hub of the urban area, heavily urbanized Northeas ...

, and New York, and of the Massanutten Formation in

, and the Clinch Sandstone farther south. Butts (1940) indicated that in the Appalachian Valley and Ridge Province the name "Tuscarora Sandstone" should be applied to these strata from Pennsylvania in the north to 38deg N latitude, and that the name "Clinch Sandstone" should be applied to these strata south of 38deg N latitude. There is one named

member Member may refer to: * Military jury, referred to as "Members" in military jargon * Element (mathematics), an object that belongs to a mathematical set * In object-oriented programming, a member of a class ** Field (computer science), entries in ...

of the formation: Castanea, occurring at the top, leaving the Lower and Middle Tuscarora Formation at the bottom. This formation has been called the "White Medina Sandstone" in West Virginia.

Fossils

Very few fossils exist in the Tuscarora, and most of them are

trace fossils A trace fossil, also called an ichnofossil (; ), is a fossil record of biological activity by lifeforms, but not the preserved remains of the organism itself. Trace fossils contrast with body fossils, which are the fossilized remains of part ...

. At least two hughmilleriid

Eurypterid Eurypterids, often informally called sea scorpions, are a group of extinct marine arthropods that form the Order (biology), order Eurypterida. The earliest known eurypterids date to the Darriwilian stage of the Ordovician period, 467.3 Myr, mil ...

s (sea scorpions) have been discovered in the Tuscarora.Boucot, A.J., Gray, Jane, and Hoskins, D.M., 1994, New hughmilleriid (Eurypterida) occurrence from the Tuscarora Formation, central Pennsylvania, and its environmental interpretation, IN Landing, Ed, ed., Studies in stratigraphy and paleontology in honor of Donald W. Fisher: New York State Museum Bulletin, no. 481, p. 21-23.

Age

Relative age dating of the Tuscarora places it in the Lower

period, being deposited between 440 and 417 (±10) million years ago.

Interpretations of 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 Tuscarora has always been interpreted as mostly terrestrial or shallow marine deposits resulting in a

molasse __NOTOC__ In geology, "molasse" () are sandstones, shales and conglomerates that form as terrestrial or shallow marine deposits in front of rising mountain chains. The molasse deposits accumulate in a foreland basin, especially on top of flys ...

sequence produced by the

Taconic orogeny The Taconic orogeny was a mountain building period that ended 440 million years ago (Ma) and affected most of modern-day New England. A great mountain chain formed from eastern Canada down through what is now the Piedmont of the east coast of the ...

. It is thought to represent a vast sand shoal along the margin of the Iapetus Ocean.

Ripple marks In geology, ripple marks are sedimentary structures (i.e., bedforms of the lower flow regime) and indicate agitation by water ( current or waves) or directly by wind. Defining ripple cross-laminae and asymmetric ripples * ''Current ripple ...

are seldom found, but do support interpretation as a shallow marine depositional environment.

Economic uses

The Tuscarora may have been used as a ganister for making furnace liners in 19th century

iron Iron is a chemical element; it has symbol Fe () and atomic number 26. It is a metal that belongs to the first transition series and group 8 of the periodic table. It is, by mass, the most common element on Earth, forming much of Earth's o ...

smelting Smelting is a process of applying heat and a chemical reducing agent to an ore to extract a desired base metal product. It is a form of extractive metallurgy that is used to obtain many metals such as iron-making, iron, copper extraction, copper ...

blast furnace A blast furnace is a type of metallurgical furnace used for smelting to produce industrial metals, generally pig iron, but also others such as lead or copper. ''Blast'' refers to the combustion air being supplied above atmospheric pressure. In a ...

s of central Pennsylvania. The Tuscarora has become very important to the tourism industry of eastern West Virginia, where the formation has many conspicuous outcrops visible from such roads as U.S. Routes 33 and 50 and West Virginia Routes 28 and 55. Tuscarora-capped North Fork Mountain and various Tuscarora cliffs are prominent in scenic views from such sites as

Spruce Knob Spruce Mountain, located in eastern West Virginia, is the highest ridge of the Allegheny Mountains. The whale-backed ridge extends for only from northeast to southwest, but several of its peaks exceed in elevation. The summit, Spruce Knob (), ...

and Dolly Sods.

Pendleton County, West Virginia Pendleton County is a county located in the U.S. state of West Virginia. As of the 2020 census, the population was 6,143, making it the second-least populous county in West Virginia. Its county seat is Franklin. The county was created by the ...

, has become a world-renowned

rock climbing Rock climbing is a climbing sports discipline that involves ascending climbing routes, routes consisting of natural rock in an outdoor environment, or on artificial resin climbing walls in a mostly indoor environment. Routes are documented in c ...

location. It is the only "true peak" (a peak inaccessible except by technical

techniques) on the East Coast of the United States. Two climbing schools near the outcrop and many other guide services offer guided climbing trips on the 300+ climbing routes on the west-facing cliff.

is managed by the U.S. Forest Service, and is located within the Spruce Knob–Seneca Rocks National Recreation Area of the

Monongahela National Forest The Monongahela National Forest is a U.S. National Forest, national forest located in the Allegheny Mountains of eastern West Virginia, US. It protects over of federally managed land within a proclamation boundary that includes much of the Po ...

. The Nelson Rocks Preserve, located near Circleville, West Virginia, is a privately owned and operated nature preserve dedicated to preserving Nelson Rocks and the surrounding environment as a cultural, educational, and recreational resource. The preserve offers a

via ferrata A via ferrata (Italian language, Italian for "iron path", plural ''vie ferrate'' or in English ''via ferratas'') is a protected climbing route found in the Alps and certain other Alpine locations. The protection includes steel fixtures such as ...

climbing trail, one of six in the United States.

References

{{Stratigraphic column of West Virginia Silurian System of North America Quartzite formations Sandstone formations of the United States Shale formations of the United States Siltstone formations of the United States Silurian United States Silurian Maryland Silurian geology of Pennsylvania Silurian geology of Virginia Silurian West Virginia Cliff-formers Aeronian Telychian