HARPERS FERRY HISTORIC PARK

GEOLOGY

MARYLAND & WEST VIRGINIA U.S.A

 

The

ROCK LAYERS

The

WEVERTON FORMATION

The formation is metamorphosed alluvial sediment formed at the base of a transgressive marine sequence, it represents the change between volcaniclastic and fluvial sediments. The river environment that placed the Weverton Formation shows a paleocurrent direction towards the west when the sandstone, siltstone and shale were placed before the formation was metamorphosed. 

Metamorphic rocks in the Weverton Formation:

The formation is comprised of 600 feet of folded quartzite which is a non-foliated metamorphic rock which was once quartz sandstone. Greywacke is a form of sandstone that is poorly sorted dark in colour and is in a clay matrix, this type also contains smaller rocks forming a more conglomerate like texture. Phyllite is a foliated medium-grade metamorphic rock that was once fine-grained shale and is the third rock type shale turns into when metamorphosed. The name metamillstone is used when siltstone has gone under metamorphism to some degree. Metagreywacke is a mix of quartzose chlorite/biotite schists that contain very fine-to course-grained granules of blue quartz.

The Weverton Formation is comprised of 3 different members:

. Buzzard Knob Member

The Buzzard Knob Member is 160 feet thick with the lower 50 feet of the member comprised of thin-to-medium bedded light-grey to greenish-grey chloritic coarse-grained to very coarse-grained quartzite. Trough cross-bedding is characteristic of the Buzzard Knob Member where the environment that deposited it was angled to the ancient current.

. Maryland Heights Member

The Maryland Heights Member weathers much faster than the above and below sections of the massive quartzite in the other sections of the Weverton Formation. Other rock types in the member include altering medium-grey quartzite and medium-dark grey conglomeratic greywacke, dark-grey phyllite and metasiltstone. Phyllite and highly folded metasiltstone between the Buzzard Knob and Owens Creek Members are deformed to a degree where the stratigraphic characteristics are almost completely obscured.

. Owens Creek Member

The Owens Creek Member is the upper member of the Weverton Formation and is more resistant to weathering than the other two lower members. The member rarely forms ledges like the Buzzard Knob Member and has more exposures compared to the Maryland Heights Member. The member consists of dark-grey interbedded phyllite and thin-bedded, coarse-grained, dark-grey metagraywacke. The visible lower 50 feet of the member consists of medium-grey medium-bedded, course to very coarse-grained quartzite along with granular conglomerate. The remaining 90 feet of the member is comprised of interbedded, medium-to dark-grey thin-bedded coarse-grained greywacke. Dark-grey quartzite with pebble conglomerate, several greenish-grey quartzose, ferruginous (Iron Cemented) siltstone is also apart of the upper section of the member.  

The Maryland Heights Trail (Photos Located Below) is comprised of the Owens Creek member of the Weverton Formation across the river from the town of Harpers Ferry. 

HARPERS FORMATION

The tilted Harpers Formation is located below the Owens Creek Member of the Weverton Formation, both formations dip to the southwest in Harpers Ferry. To the north at the Pennsylvania Maryland state line, the formation is dominated by more quartzites. 

The formations name has been changed three times since 1893, the first name being the Harpers Ferry Shale than to the Harper's Shale again by Keith in 1894 and to the current Harpers Formation.

The formation is comprised of an interval of shale, siltstone, sandstone, and quartzite. The lower section around Harpers Ferry is comprised of several hundred feet of dark-grey to olive-black, medium-grained sandstone and siltstone with 1-4 inches of medium-grey, fine-grained sandstone.

 

Above the sandstone are 700-1000 feet of greenish-black to brownish-black, highly cleaved siltstone, fine-grained sandstone and silty shale.  Greenish-black/olive-gray and brownish-black medium-bedded/medium-grained sandstone layers, ranging from 20-40 feet are visible at the entrance to the historic park in Harpers Ferry. 

 

The very top layer is comprised of interbedded dark-greenish-grey to olive-black sandy siltstones and shales, fine-grained sandstone with beds 2-6 inches thick and is light/medium-grey in colour. The very highest section of the formation ranges in thickness from 500-700 feet.

 

Skolithos burrow trace fossils are also visible at the top section of the formation which were once found in a shallow marine environment and were used for feeding.    

WATERFALLS

The Ojo Alamo Formation contains the majority of the petrified wood 

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REFEreNCES

Southworth, Scott, Brezinski, D.K., Orndorff, R.C., Logueux, K.M., and Chirico, P.G. (2000).​ Digital geologic map of the Harpers Ferry National Historic Park, Open-File Report OF-2000-297, USGS.

David K. Brezinski, Emery T. Cleaves, Director Department Of Natural Resources, Maryland Geologic Servey, Lithostratigraphy Of The Western Blue Ridge Cover Rocks In Maryland, Report Of Investigation NO. 55

Richard P. Nickelsen, (March 1st, 1956). Geology Of  The Blue Ridge Near Harpers Ferry, West Virginia, 

The University of Maryland, Department of Geology, (2019).  Sedimentary structures I, GEOL 342 Sedimentation and Stratigraphy, Fall Semester.

Genus: Skolithos, Fernández & Pazos, (2012). Fossil ID.info.

Scott Southworth and David K. Brezinski, Geology of the Harpers Ferry Quadrangle, Virginia, Maryland, and West Virginia, Prepared in cooperation with the Maryland Geological Survey, the National Park Service, and the Loudoun County Department of Environmental Resources, U.S. GEOLOGICAL SURVEY GORDON P. EATON, Director, U.S. DEPARTMENT OF THE INTERIOR BRUCE BABBITT, Secretary, U.S. GEOLOGICAL SURVEY BULLETIN 2123