Donald Kenney (donaldkenney@gmail.com)
Last Update: Tue Jun 5 06:23:42 2012


A thick sequence of Upper Silurian and Lower to Middle Devonian marine rocks is exposed in the area where the states of New York, New Jersey, and Pennsylvania meet.

The Site(s)

Port Jervis, NY-Matamoros, PA-High Point, NJ lie at the junction of Pennsylvania, New York, and New Jersey. Upper Silurian and Lower Devonian marine beds are well exposed in the area. One well known site called Trilobite Mountain is in New York. The beds continue in New Jersey SouthEast of Port Jervis as a ridge on the East Side of the Delaware River called Wallpack Ridge which extends about 35-40km SouthWest to Wallpack Bend on the Delaware River. Trilobite Mountain per se is a NE-SW trending ridge just East of the Neversink River. It is about 3.2km long and 1.6km wide and represents erosion resistant beds between the Middle Devonian Marcellus shales of the Neversink River Valley on the NorthWest and a swamp developed in the Upper Silurian Manilus/Medina beds to the SouthEast. Several quarries on the SouthEast side of the ridges figure prominently in 19th Century paleontology These include Bennett's Quarry, Nearpass's Quarry (New Jersey) and Buckley's Quarry.

NB. Shimer's 1903 paper describes the the exposures as being 4.8km SouthEast of Port Jervis whereas they appear to start a kilometer or so East of Port Jervis and to extend North and slightly East. Since neither the town of Port Jervis nor the Neversink River -- which Schimer cites as the Western boundary of the region -- appear to be very mobile, it is difficult to account for this discrepancy.

Trilobite Mountain as described by Schimer is an exposure of over 500 meters (1600feet) of Upper Silurian and Lower to Mid Devonian limestones and shales with the older rocks on the SouthEast side and the younger ones on the NorthWest side. There are a number of minor NorthEast to SouthWest ridges on the mountain exposing the more resistent rocks and leaving the minor slopes to their SouthEast covered with talus. However, it is reported that cleavages in the visible rocks often does not match the actual NorthWest dip of the beds.

NB. The name not withstanding, most of the fossiliferous rocks exposed on the Trilobite Mountain ridges will not contain trilobites. Shimer cites a Phacops a few times in the Westernmost Middle Devonian Onondaga Limestone exposures. The trilobite rich layer apparently is a 7-15 cm (3-6 inch) limestone bed at the base of the Lower Devonian Oriskany Limestone that contains abundant fragments of Dalmanites and Homalonotus. This bed should be about 50 meters below the transition from the fossiliferous Oriskany Limestone to the very thick, and non-fossiliferous Esopus Grit.



41.3591N,-74.6744W Lat Long is the junction of Old Greenville Turnpike and Lime Kiln Road at the SouthEast end of the ridge.

Directions to the site

Access to Trilobite Mountain is reported to be via hiking trails from a trailhead on Old Greenville Turnpike which crosses US6 (Slate Hill Road) NorthEast of Port Jervis. This should be the first road on the left as one approaches Port Jervis from the East on US6, but I'm guessing that one would want to turn right, not left, at the junction of Old Greenville Turnpike and US6 in order to find the trailhead. I'd print or purchase some maps before I tackled this one, unless the objective is a nice, but aimless, hike in the woods.

Note: checked 110512 - There does not seem to be a trailhead on Old Greenville Turnpike - Possibly it is on Limekiln Road or Hidden Valley/Lenape Road Further research says the trailhead is white blazed and is adjacent to 18 Old Greenville Turnpike. There is reportedly parking for one (1) compact car at the trailhead.



Rules and Access

Who knows? The area is a hodgepodge of public and private land in two states with poorly defined access points. Fossil collecting seems to be permitted along the hiking trails on the Trilobite Mountain ridge. Access is asserted to be from a trailhead on Old Greenville Turnpike.

Related Localities


The Geology section (following) lists common/index forms for the various formations. See Shimer's report Siluric and Lower Devonic Faunas of Trilobite Mountain. H.W. Shimer for detailled faunal information.


Formations (youngest first)

Other Stuff


Copyright, Licensing, and such

Copyright 2010 Donald Kenney (Donald.Kenney@GMail.com). Unless otherwise stated, permission is hereby granted to use any materials on these pages under the Creative Commons License V2.5 see http://creativecommons.org/licenses/by/2.5/.

This page will be validated as Valid HTML 4.01 Transitional before posting. Logo Image omitted.