Interstate highway 80 road cut, Jenny Jump Mountain, Allamuchy Township, Warren County, New Jersey, USAi

Regional Level Types
Interstate highway 80 road cut	Road Cutting
Jenny Jump Mountain	Mountain
Allamuchy Township	Township
Warren County	County
New Jersey	State
USA	Country

A large road cut for Interstate 80, excavated in the late 1960's. The cut exposes a conspicuously layered sequence of calc-silicate gneiss. Most of the rocks exposed in the cut were mapped by Drake and Lyttle (1985) as Quartz-Plagioclase-Epidote-Biotite gneiss. When this author examined the cut circa 1970, post excavation but pre highway, there were no exposures of any carbonate dominant lithology that would typically be called “marble”. Some layers are composed almost entirely of nearly white tremolite with minor interstitial calcite. Etching revealed a mass of small, tightly packed, sub-parallel tremolite laths with porosity of a few percent left by the dissolved calcite. An outcrop near the east end of the cut and now between the east and west bound lanes,is locally pyritic. Most of the crystals were small but occasionally larger, well formed individuals could be found.

Searching the walls of the cut, which were very fresh exposures in 1970, did not yield any sign of the Paleozoic epigenetic vein mineralization, either alpine cleft or MVT lead-zinc, that is widely scattered in the region. This is surprising given the locality's structural environment and lithologic makeup. The complex structure is discussed by Herman and Monteverde (1989).

The Jenny Jump Mountain cut seems not to have received any investigative scrutiny either by geologists or collectors while it was under construction or since. This author has never heard anyone speak of doing any work there.

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References