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Tonoloway Formation facts for kids

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Tonoloway Formation
Stratigraphic range: Pridoli
A Tonoloway limestone "fin" known as Blue Rock, Smoke Hole Canyon, West Virginia
Type sedimentary
Underlies Keyser Formation
Overlies Wills Creek Formation
Thickness 250+/-20 m
Primary limestone
Other shale
Region Appalachian Mountains
Extent Pennsylvania, Maryland, Virginia, West Virginia
Type section
Named for Tonoloway Ridge, Rock Ford, WV
Named by E. O. Ulrich, 1911

The Late Silurian Tonoloway Formation is a mapped limestone bedrock unit in Pennsylvania, Maryland, Virginia and West Virginia.


The basal 50 m consists of medium-dark-gray laminated to thin-bedded calcisiltite with shale partings and interbeds. Overlying 5 m are light-yellowish-gray to olive-gray mudstone and shale. Above this interval are 75 m of laminated calcisiltite with interbeds of thick to very thick bedded calcisiltite. The remainder of the formation is cyclic, consisting of three or four resistant ledges of laminated limestone and shale. Uppermost 20 m contains a variety of limestones. Lower contact with the Wills Creek is probably conformable. Upper contact is conformable and undulatory, occurring at the base of the "calico" limestone of the Keyser Formation.

Depositional environment

The depositional environment of the Tonoloway is interpreted as shallow marine.

Notable exposures


Relative age dating places the Tonoloway in the late Silurian.

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