HARPERS FORMATION

Harpers Ferry, mileage 60.6

       Nearest Access: Harpers Ferry Potomac bridge, mileage 60.67                     

  The Harpers is a thick assemblage of phyllitic metasilstone that contains interbeds of metamorphosed arkose and pebble conglomerates near its base and magnetite-bearing sandstones in its upper part.  The Harpers is exposed as the cliff face that extends along the Canal nearly as far as Dam 3, a distance of well over a mile.  It underlies the Weverton Formation in supporting the western flank of the Blue Ridge through Virginia.  Trails that ascent Maryland Heights cross the Harpers and afford opportunities for close observation of its rock units.  It has been highly distorted and faulted by tectonic activity; its predominant trend here is vertical or even somewhat overturned beyond the vertical.

There is evidence of life during Harpers time in the form of trace fossil worm tubes attributed to the genus, Skolithos.  These, along with evidence of sorting in the sandstone members, suggest that the Harpers was deposited in a marine environment, a continuation of the transgressive seashore established earlier during Weverton deposition.  Although magnetite was sought as an ore for iron in the 18^th century, the Potomac Valley was not well endowed with it.  As a result, magnetite recovery was many times less profitable along the Potomac than limonite, hematite, and siderite (the carbonate of iron) that supported the early iron industry.

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