ORISKANY SANDSTONE        

Site Locations: (4) 

Lock 55, mileage 134.10

     Nearest Access: Woodmont Road, mileage 134.50

Potomac Forks Camp, mileage 165.24

     Nearest Access: Oldtown, mileage 166.70

 Spring Gap, mileage 173.20/173.60

     Nearest Access: Spring Gap Camp, mileage 173.37

 Lock 72, mileage 174.50

     Nearest Access: North Branch Visitor Center, mileage 175.50                                            

The Oriskany is a very important rock formation commercially.  In areas where it is encountered at depth, it is an important natural gas bearing formation.  In the immediate vicinity, Berkeley Springs/Hancock, it has been quarried for many years as a glass sand.  The exposures that can be seen across the river in West Virginia from the Canal at approximate Mile Markers 125/128 are of an immense quarry that is now operated by U.S. Silica.  Upstream of the North Branch Visitor Center are the building remains of a Pittsburgh Plate Glass Factory, Mile Marker 176, that operated with Oriskany sand.  The Oriskany was long prized as a source of silica for manufacturing the very finest of crystal glass products.

  The Oriskany is a remarkably pure white quartz sandstone that often can be easily crumbled where it has been exposed to weathering.  That is because the cement that holds the quartz grains together is predominantly calcium carbonate.  Its depositional environment was marine as witnessed by the profusion of brachiopod casts that are characteristic of Oriskany exposures along the Canal.  At Lock 55 there is a fossiliferous Oriskany boulder that can be examined, presumably broken off the ledge that is located along the railroad bed above the lock.  The Oriskany is a ridge former, its mechanical competence demonstrated at the Potomac Forks site and at Round Top where it forms an anticlinal arch above the carbonates at about Mile Marker 128.

  The Oriskany was not widely used as a construction stone along the Canal, perhaps because of its proclivity for weathering.  However, it was cut and dressed in the vicinity of Spring Gap and used in the construction of the bridge abutments for the Patterson’s Creek bridge at mileage 173.64.  The bridge itself was destroyed in May of 1861 by Confederate sympathizers in Virginia in a concerted effort to neutralize communications and Federal troop crossings of the Potomac.

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