Chimney Rocks, Geological Area - Hollidaysburg, Pennsylvania, USA - Places of Geologic Significance on Waymarking.com

The Chimney Rocks Geological formation sets to the east of Hollidaysburg Borough in a public park, named Chimney Rocks Park. There are hiking trails that lead from parking to the formation. The rocks gave long been a landmark and point of interest.

Chimney Rocks is an outstanding outcrop of towers of limestone. The rocks are beds of the Tonoloway and Keyser Formations and part of the western flank of Catfish Ridge. The ridge is mainly supported by the Keyser Formation, a limestone that is slightly more resistant than the Tonoloway Formation, and which makes up the base of the ridge. A small vertical fault is the primary cause for the development of the chimneys.

Northeast trending joints, which have enlarged by dissolution of limestone, also have contributed to the isolation of the chimneys. The Keyser Formation is noticeably fossiliferous, including crinoids, corals, brachiopods, bryozoans, and stromatoporoids.

In addition, Chimney Rocks provides a scenic view of Hollidaysburg and its setting in the Ridge and Valley Province.

In the distance, the imposing wall of the Allegheny Front rises to the north. This marks the boundary between the Ridge and Valley and the Appalachian Plateaus physiographic provinces.

"Keyser and Tonoloway Formations, undivided:
In descending order: Keyser Formation--medium-gray, crystalline to nodular, fossiliferous limestone; upper part laminated and mud-cracked; not present east of Harrisburg; passes into lower Coeymans, Rondout, and Decker Formations in the east. Tonoloway Formation--medium-gray, laminated, mud-cracked limestone containing some medium-dark- or olive-gray shale interbeds; lower part passes into Wills Creek Formation east and south; passes into Bossardville and Poxono Island beds in the east.

State: Pennsylvania
Name: Keyser and Tonoloway Formations, undivided
Geologic age: Devonian and Silurian
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