MAHANTANGO FORMATION

  Site Locations: 

Long Hollow, mileage 134.35

         Nearest Access: Woodmont Road, mileage 134.50

 Oldtown Cut, mileage 167.60

         Nearest Access: Oldtown, mileage 166.70

  The Devonian geologic period was a time during which the predominant rocks were siltstone (shale) punctuated by interbedded, thin to medium thick sandstones.  The Needmore, Marcellus, Brallier, and Hampshire formations, in addition to the Mahantango, comprise several thousand feet of deposits that come in various colors (gray, olive brown, red, black) mostly depending on the degree to which the environment contained carbon and was oxidizing with respect to iron.

  The Mahantango is predominantly dark gray in color, not black like the Marcellus with which it shares the exposure at Long Hollow.  The Mahantango is highly fossiliferous, mostly small brachiopods that thrived in a muddy marine environment.  Long Hollow is a favorite field trip location for middle/high school students as well as adults in continuing education programs.

  In the vicinity of Mile Marker 168, the Canal was excavated through solid rock, the Mahantango.  Only one other place along the 184.5 miles did construction crews excavate through solid rock, the Paw Paw Tunnel.  The remaining 183.6 miles was primarily a matter of excavating river terrace deposits with occasional trimming of rock ledges with black powder where additional width was required.  In this cut above Oldtown, the Mahantango exhibits a characteristic mechanical property in the manner in which it fractures.  This has the name ‘pencil cleavage’ in which the rock breaks so as to produce long, slender, uneven shards.  The debris that has collected along both banks of the cut demonstrates this phenomenon; retrieving large, coherent specimens of the Mahantango is simply not possible.  Please remember that removing even one shard from this site is against Federal law.  The Mahantango can be located off Federal land if specimens are desired.

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