B4: LOWER TO MIDDLE DEVONIAN ROCKS OF THE DELAWARE WATER GAP NATIONAL RECREATION AREA, NEW JERSEY: FRACTURE AND LITHOLOGIC CONTROL ON ROCK-SHELTERS, KARST AND GROUNDWATER FLOW
Don Monteverde
Ron Witte
Steve Domber
New Jersey Geological and Water Survey
Trenton, 08624
ABSTRACT
Kittatinny Mountain is a major ridge that crosses eastern Pennsylvania, through northwestern New Jersey and into southern New York. It is underlain by Middle Silurian Shawangunk Formation, a resistant quartz sandstone to quartz-pebble conglomerate that separates younger Silurian and Devonian carbonate and clastic sediments on the west from Cambrian and Ordovician flysch and platform carbonates to the east. Kittatinny Mountain displays a change in structural trend from northeastward to northward near an exposure of Upper Ordovician nepheline syenite, part of the Beemerville Intrusive Complex. Westward this same structural trend is marked by upright and northwest directed overturned folds and well developed cleavage in Pennsylvania, which becomes a broad zone of gently dipping formations generally devoid of a penetrative cleavage in New Jersey. Here outcrop widths of the units are doubled. Tight and overturned folding with cleavage development and an associated decrease in outcrop width reappears farther to the north across the New York border. This undeformed zone widens to the west creating bowed margins on maps and DEMs with the syenite body at the center of the bow.
Did the Beemerville Intrusive Complex form a rigid block that created a strain shadow against Alleghenian westward directed compressional deformation? Preliminary field data in conjunction with regional gravity and seismic reflection studies while not definitively pointing to this hypothesis as the only possible conclusion it also does not negate it as a possible answer. Other possible explanations exist including indentor-controlled variability and margin-controlled geometry for example which require further research. At this point we favor an interaction with a foreland obstacle, the Beemerville Intrusive Complex.
The strain shadow creates an impact on weathering and groundwater flow as compared to the more highly deformed regions to the north and south. Karst development has to date only been found within the strain shadow, mainly in the Onondaga Limestone where beds dip uniformly gently to the northwest. Here joints, enlarged by dissolution, dominantly control groundwater flow. Other reactions of weathering to this change in structural style along strike are investigated such as joint cave development in non-carbonate rocks.
INTRODUCTION
The advent of DEM’s (digital elevation models) and LIDAR (acronym for Light Detection and Ranging) as well as Google Earth has allowed the investigation of the detailed landscape without leaving the office.
These tools are especially helpful with the geology of northwestern New Jersey. Using these tools, one sees a long curving ridge stand out in the topography that trends westerly out of eastern Pennsylvania, turning more northeasterly through New Jersey and more northerly into New York. Its name depends on its location, Blue Mountain in Pennsylvania, Kittatinny Mountain in New Jersey, and Shawangunk Mountains in New York (figure 1). It also forms a geological time break in that older rocks from Ordovician to Mesoproterozoic lie to the east and the younger rocks ranging from Silurian and younger to the west. One particular feature is an apparent nearly doubling of the outcrop width in New Jersey between Kittatinny Mountain and the Delaware River. Several different belts of rocks increase in width across the Culvers Gap, Branchville, Milford and Port Jervis South quadrangles (figure 1).
The best place to observe this morphologic change in the field is from High Point State Park in northwestern New Jersey. At the High Point monument (figure 1), beautiful vistas are open in all directions that offer a good vantage point to observe the changing topographic expression of the regional landscape. The visible topography is mostly controlled by the underlying bedrock with locally a blanket of thick glacial deposits. The ridge is the Middle Silurian Shawangunk Formation with the younger Bloomsburg Red Beds forming the western slope of Kittatinny Mountain. In a visual traverse beginning in the northwest, the distant ridges comprise the gently tilted Devonian and younger rocks of the Appalachian Plateau termed the Poconos in Pennsylvania and Catskills in New York. Northward is the termination of the Shawangunk Mountains/Formation. Eastward, there is a multilayered assemblage of rocks in both type and time. Just below the overlook the sandstone, greywackes and slates of the Ordovician Martinsburg Formation are visible. Farther afield are well-defined ridges in the Hudson and New Jersey Highlands consisting of Mesoproterozoic metamorphic rocks related to the Grenville Orogeny. A linear valley between the low lying Martinsburg ridges and the metamorphic ridges, named Kittatinny Valley in New Jersey, contains a belt of Cambrian and Ordovician carbonate rocks that lay in a recess position due to their higher degree of erosion. Southward, Kittatinny Mountain swings westward into Pennsylvania.
This field trip is not to investigate the reasons for this increased width of the exposed Middle Devonian through Middle Silurian rocks, though we will present two possible explanations. The field trip will offer examples of how the structural imprint, related to this increase of the outcrop belt, plays a role in many different features such as karst, groundwater flow, and habitation by early man.

B4: LOWER TO MIDDLE DEVONIAN ROCKS OF THE DELAWARE WATER GAP NATIONAL RECREATION AREA, NEW JERSEY: FRACTURE AND LITHOLOGIC CONTROL ON ROCK-SHELTERS, KARST AND GROUNDWATER FLOW

STOP 1a: Jager Road (near Brau Kettle), Sandyston Township, New Jersey
Location 1a-1 – Creek bed just downstream from culvert 1 (fig. 1-15) near Schoharie – Onondaga contact.
Features - Large solution joints, Onondaga Limestone (Edgecliff Member) and swallow hole along left bank.
Discussion – Here the Onondaga limestone forms the creek bed, which is primarily a bedding-plane dip slope cut by several large solution joints (fig. 1-16). The rock is a thin to medium-bedded, fine-grained, faintly nodular, non-cherty, sparsely fossiliferous limestone. Given its proximity to the Schoharie contact, the limestone probably belongs to the Edgecliff Member. Large crinoid columnals that are used to define Onondaga’s base have not been found near stop 1. However, the scarcity of outcrops due to dip slope geometry and burial by glacial cover in this area makes their discovery fortuitous at best. The main point to take away from this “blah, blah, blah” discussion is that the lower Onondaga in Karst Park is non- to sparsely-cherty and that is where many of the sinkholes occur.
Systematic joints in the Onondaga generally are aligned along two major trends (fig. 1-2). Enlargement of these joints and their intersections over time by dissolution, as well as minor bedding-plane dissolution has resulted in an extensive, integrated network of subsurface conduits (will discuss further at Stop 1b, Brau Kettle). The long axis of oval to trough-shaped sinks and lines of multiple sinks in Karst Park are aligned along these trends showing that karst features are strongly controlled by jointing (probably not an epiphany to most, but the lead geologist at this stop has a surficial geology background and is amused by simple observations). Solution along joints has resulted in various forms. In most places, joint surfaces are straight-walled to slightly curvilinear. Elsewhere, digitate forms (fig. 1-16) are observed, the result of dissolution along closely-spaced orthogonal to perpendicular joint sets. Also, in a few places, short, narrow openings occur that suggest a distinctive vertical component to dissolution.
A small swallow hole is found along near base of cascades, along the stream’s left bank below the roots of a small tree (fig 1-17). The swallow hole is following a large joint (020° trend), draining southwest. It is now partially covered in debris (mostly gravel). Scraps of screening and rebar (also found at other swallow holes) show manmade interference with natural flow conditions. These efforts generally fail, but once in a great while they’re thwarted by inquisitive geologists (ask Don). Most of the time this area was observed, about 70% of stream flow entered the swallow hole. Remaining flow continued downstream toward the left-hand bend eventually disappearing into the channels coarse alluvium. Over the last few years, flow many times has been observed to continue downstream past the bend to Stops 1a-2, 1a-3, and 1a-4 (fig. 1-15). The main reason for this is that the swallow hole at Stop1a-1 has become partially blocked with gravel and debris, material washed in during periods of storm-related discharge or maybe Don (the geologist not the rock) had something to do with it.
Head downstream to Stop 1a-2 either by following the stream bed (only if it’s dry) or by following the stream’s left bank. The small pit you pass on your right supplied sand to local denizens. The sand is eolian, blown off late Wisconsinan glacial outwash braid plains in nearby Minisink Valley. The sand is part of an extensive eolian sheet that has been found as much as 200 feet (61 m) above the valley floor. Just north up Stop 1-b, small sand dunes as much as 5 feet (2 m) high, cover the east side of the valley (a story for another time).
Location 1a-2 – Creek bed downstream from left hand bend.
Features - Buried swallow hole below slump, Onondaga joint-blocks, coarse gravel bar.
Discussion – Stream flow to location 1a-2 is rare. During a field trip to this area in February, 2016, the typical view of stream flow downstream from culvert 1 (the one where the stream disappears before the bend) was not so typical. Upon arriving at location 1a-2, two observations stood out: 1) most stream flow (∼ 75 %) was disappearing into an area of boulder alluvium beneath a small slump along the channel’s right side (fig. 1-18) and the remaining flow was diverted around a coarse gravel bar (located just upstream from the slump) to a small swallow hole located along the streams left bank at Stop 1a-3.
The sinking stream was probably draining into a large open joint that may have been open for observation at one time. However, recently slumped sediment (eolian sand overlying till) and Onondaga joint-blocks have covered the swallow hole. It appears that under natural conditions, variable discharge along reaches between swallow holes may be due to blockage of swallow holes upstream. Over time, the cyclical filling and emptying of swallow holes (collapse into sink holes or erosion by running water) has resulted in a complex stream flow history. Also, heavy precipitation may overwhelm the capacity of the swallow holes to drain the creek, and channel bars may also divert flow around or to swallow holes.
Onondaga joint blocks here are non-cherty and sparsely fossiliferous limestone similar to that at Stop 1a-1. Given the gentle dip of bedding (<15°), this limestone and outcrops downstream probably belong to the Edgecliff member.
Location 1a-3 – Creek bed just downstream from Stop1a-2.
Feature - Swallow hole along left bank in collapsed till.
Discussion – The swallow hole (fig. 1-19) is a small sinkhole formed mostly in till that underlies the left steam bank and hill-slope. Shallow bedrock in the stream channel just downstream from this location suggests that bedrock is very near the surface below the sink. It is very probable that this sink overlies a large solution joint or solution joint intersection. Again, it’s very rare for surface drainage to reach this location, but this year’s February storm was severe with runoff heightened by frozen ground and melting snow.
Location 1a-4 –stream channel just upstream from culvert 2.
Features – Small cave along right stream bank, joints, Onondaga Limestone
Discussion – The intersection of a large solution joint (114° ∼v) and creek channel (possibly JI) forms the opening to a small cave (fig. 1-20). The entrance is 28 inches (71 cm) wide and 32 inches (81 cm) high with the top of the entrance formed by soil and tree roots. Bedding is 021°10° NW, similar to bedding at Stop 1a-1. The large solution joint that forms the cave entrance trends 114 degrees and has nearly vertical to slightly scalloped sides (possibly eroded by sediment laden water). The 114° trend is part of a regional set of cross joints that cluster around 120 degrees. The cave floor from its entrance extends about 5 feet (2 m) before it drops another 3 feet (1 m) into a gravel choked opening. During periods of very high stream flow, the creek partly flows into the cave and over the years its floor near the entrance has filled with sand and fine gravel. As elsewhere, a small grate near the entrance does prevent most of the coarse sediment from entering the cave.
The Onondaga here is very fine grained, non-cherty, thin to medium bedded and slightly flaggy limestone. In places, silty (?) laminae with bedding parallel, curvilinear traces mark the rock’s weathered surface (fig. 1-20).
Location 1a-5 – stream channel downstream from culvert 2.
Features – Spring, small reservoir and box.
Discussion - Several small springs are located along south side of Jager Road. Here the small reservoir and box (fig. 1-21) are typical structures used to collect water where it is often directly piped down slope to another holding area. The springs and seeps found along the south side of Jager Road discharge at or very near the till/rock contact. The small stream-cut valley topographically cuts this contact and together with the northwest dip of bedding creates favorable conditions for the emergence of springs. Given the occurrence of open solution joints along the rock’s surface springs probably represent areas where water flow has been concentrated.
The new retaining wall was built after flood waters from then Tropical Storm Sandy (10/29/2012) washed out the road, nearly removing most of the eastbound lane.
Location 1a - 6 – just downstream from culvert 3.
Features – small swallow hole along right bank near right concrete abutment. Located at base of steep slope.
Discussion – Lastly, if we look downstream from culvert 3, you’ll notice a small opening (22” wide (56 cm) by 16” (41 cm) high) along the stream’s right bank just below the concrete abutment (fig. 1-22). Just past the opening the swallow hole’s floor drops 3 to 4 feet into a small trough that trends about 55 degrees. The trough walls are partially bounded by outcrop, suggesting that this opening is following a large solution joint. Similar to the cave at Stop 1a-4, soil and tree roots form a ceiling. The opening has increased in size four fold over the last two years. Presumably, decreased subsurface discharge upstream due to sediment infilling of swallow holes, has increased discharge in the creek’s lower reaches. These hydraulic modifications are episodic and may only take one or two good storms to greatly alter stream flow.
Below culvert 3 (fig. 1-15) most of the stream drains into the swallow hole directly or seeps through the gravelly alluvium adjacent to it. Downstream the creek is usually dry until input from a small spring below culvert 4. From here discharge seeps into boulder alluvium within 100 feet (30 m) of where the spring enters the channel. Normally the creek is dry downstream until it picks up outflow from Brau Kettle.

STOP 1b. Brau Kettle (spring and sinkhole)
Location – 125 feet south of Old Mine Road and Jager Road intersection.
Features – Brau Kettle (spring and sinkhole)
Brau Kettle is a unique sinkhole-spring located along the eastern edge of Minisink Valley near the intersection of Jager Road and Old Mine Road in Sandyston Township, New Jersey (fig. 1-2). References to the kettle go back to the early French and Dutch settlers. The name was likely derived from the Dutch word for “brewing” or “boiling” (Dalton, 1976), a fitting description of the spring during discharge.
The kettle (fig. 1-23) is a conically shaped depression approximately 10 feet (3 m) deep by 20 feet (6 m) wide with its floor located in till. The sloping walls of the kettle are in thin wind-blown sand and till. Depth to rock is unknown, but given the kettle’s geometry and discharge history, it is assumed that the Onondaga Limestone is very near the kettle’s floor. Brau Kettle can be classified as an intermittent spring that varies from dry, to partially filled, to spilling; with highly variable fill and spill periods. A hydrogeologic investigation of Brau Kettle and its relationship to the Onondaga Limestone commenced in 2008 by the New Jersey Geological and Water Survey under a research permit granted by the National Park Service. This investigation consisted of measured hourly water level data using an ADR logger from the kettle and a nearby domestic well, precipitation data, and kettle discharge measurements.
It is hypothesized that the kettle was formed when a near-surface solution feature (joint or joint intersection) in the Onondaga Limestone enlarged to the point where the overlying surficial materials collapsed creating a sinkhole. Over time the flowing groundwater removed most of the finer materials leaving a boulder lag on the kettle’s floor. Because the kettle is well above the Delaware River near the base of Wallpack ridge, groundwater only rises in the kettle during wet recharge periods. Farther downstream (closer to the Delaware River) is a series of perennial springs which discharge (in a boil-like fashion) through glacial outwash and postglacial alluvium. The lower elevation springs can be thought of as the perennial “base-line” discharge points and the kettle can be thought of as the overflow or relief valve when groundwater levels are elevated and discharge is high through the local joint-controlled hydrogeologic system.
Figure 1-24 shows selected water-level elevation data for the kettle and a nearby domestic well and precipitation data. The numbered descriptions below refer to the corresponding number on Figure 1-24. 1) Dashed grey line is elevation of base of kettle outlet channel; kettle elevations above this indicate that the kettle is discharging to the adjacent stream. When the green line is flat at approximately 434 feet (132 m), the kettle is dry. 2) Water levels in the well and kettle increase in response to precipitation/recharge on Oct 28th. 3) Water levels in the kettle and well recess. 4) Rate of decline increases once kettle stops flowing out outlet. 5) Kettle is dry while water level in well continues to decline. 6) Increase in well water levels due to small precipitation/recharge event, but not high enough to come above base of kettle. 7) Water levels in well increases and kettle temporarily fills in response to precipitation/recharge event. 8) Kettle fills and begins to discharge out outlet, water levels in well increase. 9) Note that water levels follow similar trend, but are at different elevations since well water level represents a composite water level from multiple zones in the aquifer; whereas kettle represents only the upper-most zone in the aquifer.
Figure 1-25 shows the period when a square notched weir was installed in the Brau Kettle outlet channel and used to measure discharge. Calibration of the manual and data recorder measurements was poor with an R-squared error of 0.79 and seepage around the edges of the weir was observed after several months of operation. The discharge estimates should be assumed approximate at best. The kettle and domestic well water level elevation can be seen rising and falling in response to recharge events as described in Figure 1-24. Discharge is observed to have occurred in the wetter winter months when Evapotranspiration is low and recharges rates and water levels are typically highest. Discharge also periodically occurs during the summer and fall for short durations when heavy rains cause significant but temporary increases in water levels. Discharge rates hover in the 500 to 1000 gpm range and peak as high as 3,500 gpm. This would make the kettle a 3rd order spring and fairly large for what is typically observed in New Jersey. Also of interest is that a nearby stream channel (located approximately 100 feet (30 m) to the north and lower in elevation that the base of the kettle) is typically dry when the kettle is actively discharging. This suggests that groundwater flow is highly constrained along joint-controlled flow paths.
Lastly, because springs may be used to determine the health of the aquifer, floral and faunal studies have been conducted throughout New Jersey (biologists and geologists working together, hmmmm. another sign of the apocalypse). Figure 1-26 shows a recent monitoring of Brau Kettle where a brook trout was captured. An additional study by NJGWS, monitors spring chemistry and temperature. Water samples collected between 10/18/2012 and 7/26/2013 show a range of pH between 7.0 and 7.5 with temperature ranging between 8.6 to 12.0 centigrade.

STOP 2a. Dingmans Ferry Spring
Geologic Setting The same as Stop 1. We are still on the northwest flank of Wallpack Ridge formed here by a gentle dip slope of the Onondaga Limestone. In most places, the slope is covered by thin till. Along the Delaware River, glacial and postglacial terraces flank the river. The field stop route will traverse the lower and older part of the Onondaga first followed by a short ascent to the younger part of the formation. The lower part of the Onondaga is non-cherty (similar to that observed at Stop 1-1a) whereas the upper part is very cherty. Large crinoid columnals that define the base of the limestone were observed by Spink (1967) along County Route 560, located about one mile (1.7 km) from the parking area. The columnals were confirmed by the trip leaders and several more were found nearby along strike.
Location – Lower slope of Wallpack Ridge.
Features – Dingmans Ferry spring, large solution joints, Onondaga Limestone (Edgecliff Member) and tufa.
Discussion – The spring (fig. 2-2) flows out of a large solution joint (070°), and emerges from a large opening at the base of a slope break. From here it spills downstream, cascading over a lag of till stones before coalescing into single channel. A very large oak tree (5-foot (1.5 m) diameter) stands sentient next to the spring, drinking its cool water for centuries. Building ruins below near Old Mine Road (fig. 2-1) and a nearby spring box suggest settlers used the spring for potable water. Evidence of Amerind history in the area (Schrabisch, 1915) suggest the refreshing spring water was enjoyed well before this wild area was settled by colonists. Given the proximity of the spring, cave, and chert resource to each other, this area was probably sacred to the Minsi Lenapi that lived along the banks of the Delaware river.
Tufa, porous calcium carbonate (fig. 2-3), covers many of the rocks near the spring. It was deposited by emerging spring water, following a decrease in pressure (subsurface to atmospheric) resulted in the precipitation of CaCO3. Water samples collected by NJGWS show pH values ranging from 7.25 to 7.42 and total dissolved solids ranged from 161 to 179 ppm; all measurements typical for springs in this area.
The nearby creek bed (fig. 2-1) is lower along contour from the spring and is typically dry. Here the Onondaga Limestone forms the creek bed, primarily a bedding-plane dip slope cut by several large solution joints (fig. 2-4). The limestone exposed along the creek bed is a thin to medium-bedded, faintly nodular, non-cherty limestone with some fossils. Its lithology is similar to the Onondaga observed at Stop 1a, so it may belong to the Edgecliff member. Similar to the situation at Brau Kettle, the lower and dry creek next to the spring shows that groundwater flows along strata-bound solution joints. Upstream a few small seeps discharge into the channel and a small wetland also drains into the channel as well as a small stream that flows off the hill-slope above the spring and well above the Schoharie – Onondaga contact. Present hydrologic conditions do not explain erosion observed along the creek. Perhaps the channel may have been cut by glacial meltwater or postglacial stream flow prior to a change in subsurface drainage and the formation of Dingmans Ferry spring.
Recently, the spring’s small stream was diverted to a larger channel (fig. 2-1). Spring discharge can now be observed flowing into the dry channel just upstream from the culvert on Old Mine Road. This manmade diversion was in response to erosion abatement and icing along Old Mine Road.
Proceed across dry (hopefully) creek bed and head upslope. Safety Alert. Be very careful crossing channel. If wet, the sloping rock surface is very slippery and may also be covered by leaves and moss. Also, watch out for a paper wasp nest near the south side of the dry creek. Hopefully, these insects will vacate the premises before our trip.

STOP 2b. Amerind chert use, Tom Quick Cave, Cherty Onondaga limestone
Geologic Setting The same as Stop 1. We are still on the northwest flank of Wallpack Ridge formed here by a gentle dip slope of the Onondaga Limestone. In most places, the slope is covered by thin till. Along the Delaware River, glacial and postglacial terraces flank the river. The field stop route will traverse the lower and older part of the Onondaga first followed by a short ascent to the younger part of the formation. The lower part of the Onondaga is non-cherty (similar to that observed at Stop 1-1a) whereas the upper part is very cherty. Large crinoid columnals that define the base of the limestone were observed by Spink (1967) along County Route 560, located about one mile (1.7 km) from the parking area. The columnals were confirmed by the trip leaders and several more were found nearby along strike.
Location – Hill overlooking the Delaware River near Dingmans Ferry and the only privately owned toll bridge across the Delaware River. Add history of Dingmans Ferry.
Features - there are three things to see, 2b-1) possible evidence of Amerind chert utilization, 2b-2) Tom Quick Cave, and 2b-3) cherty Onondaga Limestone (flinty Don). Depending on the group size, slope conditions, and whether we’re on schedule, we may stop at all three locations (fig. 2-1). Discussion -
2b-1 – Slope below outcrop.
There are many small chert fragments and a quartzite hammerstone (fig. 2-5) near the base of a tree. Because tree root growth may concentrate rock fragments on the surface (old mapping trick in areas of sparse outcrop), their occurrence here may not indicate Amerind working of this chert resource. However, some chert fragments exhibit conchoidal fractures and the hammerstone’s tip has been broken in a way to suggest it was used as a tool. Also, the hammerstone fits remarkably well into the palm of your hand. Amerinds quarried and collected chert throughout Wallpack Ridge to provide blanks for tools and projectile points (Phillip LaPorta, personal communication, 1996)). Given the location of this hill overlooking the Delaware River, proximity to Amerind encampments situated on alluvial terraces near Dingmans Ferry (Schrabisch, 1915), and abundance of chert in the Onondaga here, this site would have been a prime location to collect chert. It may have been quarried from the outcrop or collected from loose rock on the slope below. Typically, larger pieces of chert were knapped into smaller blanks at the outcrop and then carried back to encampments where they were further worked into tools such as scrappers and projectile points. Hopefully, the evidence presented shows that this site was actively used to process chert. At least that’s our story (spring, cave, chert) and we’re sticking by it.
2b-2 – Tom Quick cave.
The cave is a long, narrow slot (fig. 2-6) that runs about 25 feet (8 m) along a large joint (027°). Given the attitude of bedding (043° 12° NW) and proximity to a steep slope down dip, the cave is probably a fracture cave that formed when a very large joint block moved downslope by creep., and not the result of solution weathering. However, the initial enlargement of the joint by solution weathering cannot be discounted. In addition to creep, movement may have been aided by root growth and ice wedging. Also, evidence for solution weathering beneath cherty limestone (Stop 2b-3) may have contributed to detachment along bedding along the base of the joint block. Above the cave small sinkholes are found that are aligned along the 027° fracture.
Eye witness accounts (Bathgate, 1916) of a small room at the cave’s terminus about 55 feet from its entrance suggest the cave may have been larger than its current size. During a return visit, Bathgate could only proceed about 20 feet into the cave. One of the cave walls had moved closing off the passage. This account suggests that the cave may consist of several joint blocks that at times may move independently from one another.
As with most caves, local lore provides interesting stories where fact is not easily separated from fiction. The cave is named after Tom Quick Jr., who may have used the cave as a hideout during the mid-1700’s following one or several Indian skirmishes (Dalton, 1967). Supposedly, Tom’s father, Tom Quick Sr. was mortally wounded in a raid when the family was cutting ice on the Delaware River (njherald.com/article/20151206/ARTICLE/312069975#).
Currently the cave is closed by the National Park Service in order to protect bats from a deadly fungus that causes white nose syndrome.
2b-3 – Cherty Onondaga Limestone outcrop along west side of hill.
This face offers a good opportunity to investigate the cherty beds of the upper Onondaga. Originally named the Corniferous Limestone (Cook, 1868) based on similarities cherty limestones found in Pennsylvania and New York. This 14 foot-high (4.3 m) outcrop shows an abundance of chert nodules dispersed throughout the outcrop (figure 2-7). The chert nodules vary from 2 to 3 inches (5-7.5 cm) across. Close inspection shows areas where the chertification was incomplete yielding a dark gray mottled appearance. Associated with this incomplete certification are intriguing very thin parallel black curving lines that are commonly associated with the mottled spots (fig. 2-7, inset photos). There is no preferred orientation of these thin bands, which we suggest may relate to the secondary chert-forming process. Further study is needed to completely understand this appearance.
Due to the absence of a preferred fracturing in these beds the chert would be more easily worked and highly prized by the original inhabitants of this region. Farther to the north this same cherty upper part of the Onondaga is highly cleaved which would greatly inhibit the ability to work those cherts into usable points. Beds are generally wavy with variable thickness of 3 to 8 inches (7.6-20.3 cm). At the base of this outcrop are two small solution openings (fig. 2-8) in generally chert-free beds. The solution appears to occur at the intersection of the bedding plane and some weakly developed joints trending 068°. This minor bedding plane solution may have enhanced joint-block movement down slope which led to the development of Tom Quick cave.
Given its high chert content and younger stratigraphic position relative to the basal Onondaga, we believe we are looking at the Moorehouse Member (possibly its upper part). We have not encountered the Nedrow Member in our mapping because it may not be here because it may be indistinguishable from the Edgecliff or Moorehouse Members (Oliver, 1956) or because of its shaly nature it does not outcrop along the Onondaga dip slope. The Tioga bentonite, which defines the Seneca-Moorehouse contact has not yet been encountered in western New Jersey, but as stated in the long discussion preceding Stop 1a we believe the Seneca lies mostly buried beneath alluvium and glacial outwash making its identification problematic.

Peters Valley School of Craft - Lunch Stop
Peters Valley, which is on route to Stop 3 (Bevans Rock Shelter). Park in upper lot near picnic pavilion (fig. 2-9). Rest rooms are located at the bottom of the hill across the street from the gallery. Please take a moment to stop by the gallery and checkout the many fine works of the local artisans.
Peters Valley School of Craft is a non-profit corporation, founded in 1970 in partnership with the National Park Service to promote and encourage education and excellence in craft. Peters Valley School of Craft's programs include adult summer workshops, youth programs, opportunities for artists, special studio programs, public exhibitions, demonstrations, and outreach. Peters Valley School of Craft maintains studios in eight disciplines: blacksmithing, ceramics, fiber surface design, fiber structure, fine metals, photography, special topics and woodworking. Description from https://www.nps.gov/dewa/planyourvisit/peters-valley.htm.
For more information about Peters Valley School of Craft and the programs offered, visit the campus at 19 Kuhn Road, Layton, NJ 07851, call (973) 948-5202 or visit their website at petersvalley.org.
We’ll probably spend about 45 minutes here and then take the short drive over to Stop 3 (Bevans Rock Shelter). Turn right onto Wallpack Road to continue trip.

STOP 3. Bevans Rock Shelter - Parking
Location and logistics Stop 3 is located in the Culvers Gap quadrangle in the Delaware Water Gap National Recreation Area (DEWA) on Wallpack Ridge above Peters Valley (fig. 1-1). The exact location of the rock shelter is not shown in order to protect the cultural integrity of the site. Follow trip leaders to secret parking area and then we’ll proceed by foot to the rock shelter. The large outcrop near the parking area is the Esopus Formation, a very thin to thin-bedded, very fine-grained sandstone. Bedding is 046° 16° NW and the outcrop is cut by a well-developed cleavage (081° 72° SE).
Geologic Setting
The Bevans Rock Shelter (fig. 3-1) sits high on Wallpack Ridge about one mile (1.6) km from both the Delaware River and Flat Brook in Wallpack Valley. The rocks in the shelter area are oldest to youngest are the Glenerie Formation and Ridgely Sandstone of the Oriskany Group, Esopus Formation, Schoharie Formation, and the Onondaga Limestone (fig. 3-2). All formations dip northwestward with the Onondaga forming a long dip slope to the Delaware River. The Ridgely Sandstone, which consists of thick-bedded quartz-pebble conglomerate and coarse quartz sandstone (Monteverde, 1992) may not be present over the Glenerie at the shelter, but it has been observed nearby to the south, where it thickens along strike to Wallpack Bend and reaches a maximum thickness of 32 feet (9.8 m).
Oriskany through Onondaga time represents a sea-level cycle where 1: the Oriskany Group represents a carbonate shelf to clastic sequence (beach and nearshore fluvial deposits), 2: the Esopus Formation represents deeper water deposition marked by very low fossil content and occurrence of the trace fossil Zoophycus, 3: the Schohaire Formation is a transitional unit that marks a return to shallower seas, and 4: the Onondaga represents a carbonate shelf sequence, which in places contains patchwork reefs.
The shelter rocks over the years have had several interpretations. Henry Kummel’s field sheets (1895, on file at NJGWS, Trenton, New Jersey) show that the Cauda Galli Grit (now recognized as Esopus) was mapped at the shelter with the Oriskany contact located just east of the shelter. Meredith Johnson, during a visit to the shelter in 1938 (NJGWS permanent notes on file at NJGWS, Trenton, New Jersey), indicated that the shelter rocks belonged to the Oriskany Limestone. Johnson also noted that base of the shelter contained “numerous small brachiopods of the type similar to Anoplotheca flabellites. Herpers (1952) noted that a contact between the Oriskany and Esopus occurs at the shelter and that the lower fossiliferous zone belongs to the Acrospirifer murchisoni zone of the Oriskany. Monteverde (1992) showed that the shelter lies within the Esopus Formation. Hmmm. multiple interpretations of the same outcrop, let’s see if we can add to the confusion.
Discussion
Geology of Bevans rock shelter.
Take ten geologists to an outcrop and you’ll wind up with 10 different interpretations. An old witticism to be sure, but one with a kernel of truth to it. Who’s right and who’s wrong? We’ll present the facts and you can make up your own minds. Esopus, Oriskany, or both?
The outcrop at Bevans rock shelter looks much different than the Esopus outcrop near the parking area and above the shelter, which is a dark gray, non-calcareous, very fine-grained sandstone with a well-formed cleavage. The trace fossil Zoophycos is also found throughout the shelter’s rocks. The shelter’s roof rock (fig. 3-1) is similarly described so we’re confident that this part of the shelter is Esopus. The 10.5 feet (3.2 m) section (fig. 3-1) below the roof is much different. The rock here is mostly (we did not check every bed) a thin- to medium-bedded, calcareous, very fine-grained sandstone where cleavage is not nearly as well-formed as it is in the overlying rocks. Throughout the shelter’s back wall solution voids up to 6 inches (15 cm) in diameter (most are less than 2 inches (5 cm)) are found along bedding (fig. 3-3). Also, a few dark gray, calcareous concretions (fig. 3-3) occur along bedding about midpoint between the shelter’s roof and floor. Zoophycos occurs throughout this section to at least 2 feet above the shelter’s floor (fig 3-4). Lastly, a thin bed of small brachiopods (fig. 3-3) occurs about 5.4 feet (1.6 m) from the shelter’s floor. Presumably, these are the same brachiopods observed by Johnson and Herpers, which were interpreted to be Oriskany fauna (fig. 3-3). Biostratigraphically, this is a mixed zone where Oriskany and Esopus faunas are transitional. Lithostratigraphically, a contact occurs between non-calcareous and calcareous sandstone at or just below the shelter’s roof. As far as we are aware, no one has described Zoophycos in the Oriskany. However, Brett and others (2009) indicated that a few Oriskany brachiopods were transitional into the Esopus. Spink (1967) also noted, that the lower Esopus contact in places is “gradational through an interval of several feet in which arenaceous and calcareous siltstones become interbedded with, and then are replaced by, silty limestones.” Spink’s silty limestones are probably the Glenerie Formation.
Given the best available data (one of Don’s favorite terms of escapism) and similarity to Spink’s description of the Esopus-Glenerie contact, the shelter section below the roof represents the basal, transitional facies of the Esopus Formation. The Oriskany contact lies just to the east, buried beneath a bog that flanks the shelter. However, if you want to place the contact elsewhere, that’s fine, just publish your work after we retire.
Geomorphology
The rock shelter and the smaller caves on its flanks (fig. 3-5) were shaped by glacial erosion and postglacial mass weathering. The main shelter, with its resistant Esopus roof, was chiefly formed where the easily eroded transitional Esopus rock was removed by glacial plucking and abrasion. The scalloped surfaces on the shelter’s back wall (fig. 3-3f) appear to be glacially scoured. Also, the absence of loose rock beneath most of the shelter’s roof suggests this material was removed by glacial erosion. Admittedly, some of this material may lie buried in the bog that lies adjacent to the shelter. However, given the large size of current joint blocks in and around the shelter, one would expect that some of this material should be here on the floor of the open part of the shelter. Other than smaller stones, this material was probably not moved by the shelter’s past inhabitants.
Over time, part of the shelter’s roof and walls have collapsed (specifically the north end). The result of postglacial frost wedging and slump where joint blocks became dislodged and fell away from the outcrop. Similarly, the fracture caves on the shelter’s flanks may have been formed by frost wedging. However, because bedding dips into the hillside, the movement of these very large joint blocks was not helped by gravity as it was at Tom Quick Cave (Stop 2-c). Another possibility is that ice wedging may have occurred during glaciation. Specifically, during deglaciation when overlying ice was thin and freeze-thaw cycles much more robust.
The smaller cave in the shelter (fig. 3-5) appears to be largely a result of mechanical weathering along a nearly vertical 096° joint that intersects the shelters back wall. However, dissolution in the lower Esopus beds may have aided the cave’s formation. Archaeology of the Bevans Rock Shelter
The Beans rock shelter (fig. 3-6), located in Sandyston Township, Sussex County is a prominent rock shelter that was used by Native Americans during the Late Archaic (3000 B.C to 1000 B.C.) and Woodland (1000 B.C. to 1550 A.D.) periods. This rock shelter sits about 300 feet (91 m) above the Delaware River, located halfway between the Delaware and Wallpack Valleys. The shelter has an eastern exposure and lies adjacent to a narrow bog. It has an overhanging roof that projects up to 20 feet outward from the rock face, creating a sheltered space underneath. The habitable area of the shelter consists of three parts (fig. 3-7). To the south (near fireplaces “a” and “b”) lies a typical overhanging rock, 24 feet long, which projects eight feet outward about 10-14 feet above the floor. In the center (near dislodged rocks), another overhanging rock, 22 feet long, has a roof 8 feet high projecting 6 feet, and is protected in front by two detached masses of rock, one small, the other large, lying 5 feet from the rear wall. The central section has a higher degree of enclosure due to the two detached blocks which hold up the roof and form the eastern wall. At the right is a cave-like compartment (near fireplaces c and d), 16 feet long, 4 1/2 feet wide and 6 feet high. This northern section offers the most protection. All three parts lie in an approximate straight line at the foot of a low cliff and their total length is about 62 feet. The dirt floor underneath the rock is level and composed of light sand mixed with rocks. Two archaeological surveys were conducted here, one from 1912-1913 by Max Schrabisch, archaeologist and writer and another in 1931 led by Dorothy Cross (State Archaeologist and Curator for the New Jersey State Museum). Several local collectors also reported finding material in the main shelter from time to time, but none of this was officially recorded.
Max Schrabisch partially excavated the Bevans rock shelter while making an archaeological survey of Sussex County for the state from 1912 - 1913. In the summer of 1931, from June 8 to July 7, the New Jersey State Museum and the University Museum, Philadelphia, sponsored the complete excavation of the four shelters at the Bevans Rock shelter under the direction of Dorothy Cross. These two surveys uncovered many artifacts or traces of human habitation. During the first excavation by Schrabisch, the southern open shelter (location b, fig. 3-7) yielded the most aboriginal remains while the middle section contained the least. The rear was smoke-stained and discolored by ancient fires but no relics were found on the surface. Native American relics were found from three inches to two feet below the surface. Items included both plain and ornamented pot shards, deer bones, projectile points (identified as arrow and spear points), multiple tools (drill, pestles, hammers, blades), net sinkers, many flint and jasper flakes, and at least 1000 pieces of pottery (most cord-marked) belonging probably to approximately 20 different pots were found in the three parts of this rock shelter. Also, several fire pits were excavated (fig. 3-7), some of which contained mussel shells. Figures 3-8 and 3-9 are some of the artifacts collected during the Schrabisch survey.
A second excavation was conducted in 1931 Led by archaeologist Dorothy Cross (fig. 3-10). Altogether, the second excavation produced 102 various stone artifacts (some of which included arrow points, blades, scrappers, one possible hoe, hammerstones, net sinkers, one maul, one anvil, and one rubbing stone), 11 bone artifacts, 1,428 potsherds (both cord-marked and plain), 100 fresh-water Unio shells (whole and fragmentary), three crinoid stems (possibly used as jewelry) and several thousand whole and fragmentary animal bones, a fragment of a trade pipe, and a lead bullet. Three undisturbed pits were found during this excavation. All pits showed traces of fire action and contained refuse material.
Both archaeologists who excavated the site came to different conclusions about the habitation of the site. According to Schrabisch, “based on the materials found here, the rock shelter was tenanted more or less permanently and perhaps used for winter quarters. The fireplaces suggest cooking and the pottery indicates that the women and children accompanied the men and shared their quarters.” Cross believed “the Bevans shelters were used as temporary abodes and this is attested to by the absence of permanent household equipment. Almost all of the artifacts can be associated with hunting and fishing, either directly or indirectly; though the number of potsherds is a little greater than would have been associated with a hunting or fishing camp.” Cross further stated that “if the entire contents of the shelter were available, more definite conclusions might be drawn” regarding Amerind habitation.

Bevans Rock Shelter

STOP 4. Montague Mini Mall, Montague, NJ
Location and logistics
Stop 4 is located in the Milford quadrangle along Clove Road behind the Montague Mini Mall (fig. 4-1). An exposure of the Coeymans Limestone was uncovered during quadrangle-scale mapping around 1990. A short discussion will precede a good look at this unique exposure. Please do not use your hammers at this site. We wish to protect the outcrop from further degradation so others can also enjoy this interesting outcrop.
Fractures and Weathering
This outcrop was originally excavated in the 1980’s during the construction of a self-storage facility. Since its initial exposure, the outcrop has been weathering fairly rapidly. Both regional strike and cross strike joints were originally evident across these fossil-rich carbonate beds. The strike joints, probably through dissolution and freeze thaw have forced large carbonate joint blocks to break away. Some, I am sure have been picked up for ornamental rocks in personal gardens. Only a single strike joint is visible on the back of the outcrop in the trees. However, a nice cross joint which exposes several thick calcite-filled veins lies near the southern part of this rock body (figure 4-2). The calcite veins appeared to have dissolved faster than the surrounding bedrock which enhanced the formation of large loose blocks.
Even though the fractures here tie in with the main theme of this trip, they were just used as bait to allow us to include this field stop. So read on through the following explanation and enjoy an unusual carbonate outcrop in northwestern New Jersey.
Regional Geology
Rocks of Middle Silurian through Lower Devonian age trend northeast-southwest across northwestern New Jersey (figure 4-2). To the east, gentle, upright folds occur in the Middle to Upper Silurian Shawangunk Formation and Upper Silurian Bloomsburg Red Bed. Moving up section and still eastward of our present location, lies the Upper Silurian through Lower Devonian Poxono Island Formation, Bossardville Limestone, Decker and Rondout Formations and Manlius Limestone. All are locally covered by surficial deposits. The Lower Devonian Coeymans Formation, the lower part of the Helderberg Group, is exposed in front of us. Continuing westward and sparsely exposed lies the rest of the Helderberg Group including from oldest to youngest, the Kalkberg Limestone, New Scotland and Alsen Formations and Port Ewen Shale. As one migrates still farther westward towards the Delaware River the successively younger northwest-dipping units consist of the Glenerie Formation of the Oriskany Group, Esopus (seen at stop 3) and Schoharie Formations, the Onondaga Limestone (seen at stops 1 and 2) and lastly the Marcellus Shale. Regional investigations suggest that the Bloomsburg is the youngest folded unit while the remaining younger unfolded units dip gently northwestward (Monteverde, 1992, Monteverde and Epstein, unpublished data, Drake and others, 1996). Folds in these units reappear immediately south of Wallpack Center (Monteverde, 1992) and to the north across the New York state line into Port Jervis.
Silurian and Early Devonian sediments record the paleoenvironmental change from the end of the Taconic Orogeny into the oncoming Acadian Orogeny. Workers have mapped the changing continental sediments of the Shawangunk into the marginal marine sediments of the Bloomsburg Red Beds (Epstein and Epstein, 1969, 1972). The Bloomsburg displays different sedimentary assemblages indicative of fluvial, estuarine, lagoonal, tidal flat and offshore bar and beach paleoenvironments. These rocks continue to grade upwards into the Poxono Island and Bossardville that mark the continuing transgression through a brackish supra-tidal and intertidal flats depositional environment into a carbonate depositional environment (Epstein and others, 1967; Barnett, 1970, Epstein, 1986). The overlying Decker Formation witnessed a developed carbonate shelf with minor clastic sediment influx as well as locally developed biostromal reef complexes consisting of possible corals + stromatoporoids(?). Time progressed and the sediments of the Rondout mark a relative sea level fall into restricted lagoonal and tidal flat paleoenvironments (Herpers, 1951; Epstein and others, 1967; Epstein and Epstein, 1969). Denkler and Harris (1988) used conodonts from the Rondout to identify the Silurian to Devonian boundary.
Sediments of the overlying lower part of the Helderberg Group record a deepening and corresponding marine transgression. The Manlius Limestone suggests changes from lagoonal and intertidal environments to the high-energy conditions of a carbonate shelf/ shoal and associated patch reefs of the Coeymans Formation (Epstein and others, 1967; Barnett, 1970; Smosna, 1989). Succeeding deeper shelf settings are observed in the Kalkberg sediments and into the argillaceous limestones of the New Scotland Formation (figure 4-3). In this region the overlying Alsen Formation records a minor regression and redeposition of fossiliferous cherty limestone. The same regression is marked in eastern New York by crinoidal grainstones of the Becraft Limestone. Sea level returned to subtidal conditions as shown by the Port Ewen Shale sediments (Barnett, 1970), which marked the end of the Helderberg Group deposition.
Epstein and others (1967) subdivided the different Helderberg formations into members from eastern Pennsylvania to southern New York (figure 4-4). The different members highlight the regionally shifting paleoenvironment along this carbonate margin. Because the descriptive terminology of carbonate units differs from clastic units, one not actively working in these units may become confused with respect to their meaning. Therefore, figure 4-5 outlines the terminology originally devised by Dunham, (1962), and subsequently modified by Embry and Klovan, (1971) so a non-carbonate geologist can understand the meaning of the discussion.
The Shawnee Island Member of the Coeymans Formation is the sole unit exposed at this stop. In the woods to the east the older Thacher Member of the Manlius Limestone is exposed. he overlying Kalkberg and New Scotland locally emerge from the Pleistocene cover to allow their mapping along strike to the northwest and southwest.
Patch Reefs and Flank Paleoenvironments
Along its outcrop belt from eastern Pennsylvania through western New Jersey, eastern New York and westward into central New York, the Coeymans Formation contains at least 14 isolated reef deposits (Oliver, 1960; Rickard, 1962; Epstein and others, 1967; Isaacson and Curran, 1981; Precht, 1982, 1984, 1989; Smosna, 1989). Nine-reefs have been documented in the Deansboro Member of the Coeymans Formation in the Syracuse, New York region and the remaining are in the Shawnee Island Member in northeastern Pennsylvania and northwestern New Jersey (figure 4-6). Each Shawnee Island build up is a patch reef with a central core ranging up to 160x70 m and 15 m thick, accompanied by associated flank beds (figure 4-7) (Epstein and others, 1967; Precht, 1982, 1984, 1989; Finks and Raffoni, 1989; Raffoni and Finks, 1989).
Flank Beds
Reef flank facies consist of bedded bioclastic reef debris that thin away from the reef proper (James and Bourque, 1992) (fig. 4-7). Wilson (1975) differentiates two separate facies, that of flank beds and talus. Bioclastic debris is the exclusive sediment of flank beds, while talus also contains lithoclastic material. Lithoclastic material consists of partially lithified micritic material ripped up from underlying beds. Talus facies deposits are rare compared to flank bed facies (Wilson, 1975). Tucker and Wright (1990) suggest that these flank deposits only form near wave base and are therefore grainstone dominated. High energy waves and currents washed over these skeletal debris deposits and removed all micritic material (Smosna, 1989).
Reef flanks, as seen here, contain a high content of reef debris. This material lies broken and fragmented without any accompanying micritic or lithoclastic material. Fragmental hemispherical Favosites and crinoids constitute the greatest percentage of debris (fig. 4-7). Scarce stromatoporoids are also exposed. Rare brachiopods are present, though I have yet to find any good examples. Crinoids, although not typically part of a reef complex, are exposed here as broken fragments that commonly weather in relief. The character of the limestone beds indicates a reef flank paleoenvironment. The absence of micritic material and lithoclasts suggests an environment above wave base, in strong currents, but not reef proximal enough to be considered talus. The corresponding reef could be south of this exposure as indicated by this outcrops apparent coarser grain size in that direction. Finks (oral communication, 2001) suggested that this site is proximal to a patch reef, currently not exposed.
Relative abundance of the different bioclastic material varies over the outcrop. Corals exist across the outcrop, but they dominate in the southern beds. Crinoids occur as dispersed debris and also concentrated as bed load. They are moderately sorted in the absence of coralline material. Stromatoporoids, distantly related to modern sponges are less common across the exposure.
Grain size is variable across the exposure with a general north-south trend across the central beds. A rudstone texture from fragmented hemispherical corals appears more common in the south. Across the outcrop towards the north a general grainstone texture developed from smaller coralline debris exits. The oldest beds remain as a wackestone to packstone across the outcrop that changes through younger beds as fragmental crinoid lenses that grade into a bioclastic rudstone. Having trouble following this discussion without a figure showing outcrop geometry