Geologic Provinces of the United States: Appalachian
Highlands
Ordovician and Silurian rocks
Delaware Water Gap National Recreation
Area
Photo by Jack B Epstein, USGS
Exposure of Ordovician (Martinsburg) and Silurian (Shawangunk)
rocks in Delaware Water Gap, New Jersey side. The slates of the
are Martinsburg are separated by an angular uinconformity of about
10 degrees from the resistant quartzites of the Shawangunk,
representing the Taconic orogeny. A heavy apron of talus are
derived from the Shawangunk cliffs. On the opposite (Pennsylvania)
side of the gap the Shawangunk does not dip so uniformly and is
arched (shown by the projected dashed line), allowing for the
interpretation of a flexure at the gap site. This has suggested
structural control for the location of the gap, a fact contradictory
to the hypothesis of regional superposition. Mt. Tammany is named
after a Lenni-Lenape Indian Chief who had a secret society named
after him which, through time, became the infamous Tammany Hall.
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