LOCATION: Stokes State Forest, Branchville, New Jersey.
ACCESSING THE TRAIL
Park on the northeast side of Sunrise Mountain Road near the wooden marker for the Tinsley Trail Cross Sunrise Mountain Road and walk west on the Tinsley Trail, marked by yellow circle blazes. The trailhead of the Tinsley Trail is at N 41 12.655, W 74 44.089. At the 2nd intersection of Tinsley and Glacial Geology Trails (GGT) head north on the GGT, marked by blue blazes. The intersection of the Tinsley and GGT is at N 41 12.698, W 74 44.411. The Earthcache is on the GGT, about a 15 minute walk from the parking area. You can get a trail map at the Stokes State Forest Park Headquarters, 1 Coursen Road, Branchville, NJ.
If you would like to take a longer walk, continue along the GGT, which makes a loop that rejoins the Tinsley Trail not far from where you parked. Note that portions of the GGT are a bit challenging, with some narrow sections and a few downed trees.
NOTE TO PAPERLESS CACHERS
The description of this Earthcache may be too long to be imported into your Palm or similar device. It may be wise to print it so that you can see what you need to do to log the cache.
THERE WERE GLACIERS IN NEW JERSEY???
Over the last two million years, during the Pleistocene and late Pliocene Epochs, glaciers periodically covered large areas of North America. Geological evidence shows that glaciers expanded to and retreated from the New Jersey area at least three times during the Pleistocene. The age of the oldest of these, the pre-Illinoian stage, is uncertain, but is estimated to be more than 800,000 years old. About 150,000 years ago, during the Illinoian stage, an ice sheet again covered northern New Jersey. The most recent glaciation, known as Laurentide ice sheet, occurred during the late Wisconsinan substage, about 21,000 years ago.
The Tinsley trail brings you onto a recessional morraine left by the Laurentide ice sheet. RECESSIONAL MORRAINES are ridge-like accumulations of materials that were left behind at the end of a glacier as it retreated. The outer edges of the morraine are often marked by RIDGE-AND-SWALE TOPOGRAPHY, parallel bands of ridges. Another common feature of morraines is KNOB-AND-KETTLE TOPOGRAPHY. Kettles are depressions in glacial drift that are made by the wasting away of a detached block of glacial ice wholly or partly buried in drift. Morainal kettles vary greatly in size and shape, and most contain seasonal water and have bouldery floors. Look for both features along the trails.
ERRATIC’S BEHAVIOR LEADS TO IMPRISONMENT
GLACIAL ERRATICS are rocks that have been transported by glaciers and dropped at a distance (often many miles) from their original location. Erratics are a different rock type than the local bedrock because it was common for glaciers to flow across different types of bedrock, plucking up chunks of rock as they moved.
This Earthcache is a glacial erratic imprisoned in a cage of rebar. The rock type is nephelene syenite of Ordovician age, about 420 million years old. Nepheline syenite is a dark gray to black, coarsely crystalline igneous rock consisting of the minerals nepheline, feldspar, one or more mafic (magnesium or iron-bearing) minerals such as amphibolite or pyroxene, and little or no quartz. Look for other nephelene syenite boulders along the trail.
Caged nephelene syenite erratic found along the Glacial Geology Trail in Stokes State Forest, New Jersey. This erratic was glacially transported from a small body of syenite sometime during the last ice age, about 18,000 years ago. The syenite outcrop lies 1.5 to 3.5 miles northeast of the erratic on the east side of Kittatinny Mountain and about 200 to 330 feet below its summit.
The bedrock in Kittatinny Mountain is the Shawangunk Formation, a tough and very resistant quartzite and quartz-pebble conglomerate of Silurian age, about 425 million years old. Look for rocks from the Shawangunk Formation along the trail.
The pattern of erratics across the landscape is a record of the direction that the glacier flowed. These syenite boulders were transported from an outcrop two to three miles northeast on the southeast-facing flank of Kittatinny Mountain , 300 feet below its summit. The presence of these erratics at this site indicates that the glacier moved south 500 to 700 west, a direction that cuts across the more southwesterly trend of the mountain.
Glacial erratics at the entrance to the Glacial Geology Trail. Light- and dark-colored clast below hammer handle is nephelene syenite. It is a coarse granular aggregate that consists primarily of the mineral nephelene (dark gray, short, heaxagonal crystals) with accessory orthoclase and biotite. Light-colored clasts are quartzite and quartz-pebble conglomerate derived from the Shawangunk Formation. This formation underlies the higher areas on Kittatinny Mountain forming a nearly continuous ridge from the Shawangunk Mountains in New York to Blue Mountain in Pennsylvania.
GLACIAL GARBAGE, GRABS AND GRAFFITI
Erratics aren't the only evidence of glacial globetrotting. Glaciers modified the landscape by deeply scouring valleys, grinding down and reshaping bedrock ridges, hills and slopes, and by eroding and redepositing soil and loose rock. Scratches and grooves cut into bedrock, called STRIATIONS, record the direction of glacial flow. As ice sheets moved, they plucked up boulders, gravel, sand, silt and clay. In some areas, these materials were later deposited as TILL, which is an unsorted mix of material dropped directly from glacial ice or at a glacier’s margin. Till was deposited on the bedrock surface in sheets, in streamlined hills called DRUMLINS, and in ridges called MORRAINES which mark the end of an ice sheet. In other areas, the glaciers left behind STRATIFIED SEDIMENT, which is sorted and layered material deposited by glacial meltwater streams at and beyond a glacier’s margin. Stratified sediment was laid down in valleys by rivers that drained away from the glaciers, and in glacial lakes. KETTLES are depressions in glacial drift that are made by the wasting away of a detached block of glacial ice wholly or partly buried in drift. Morainal kettles vary greatly in size and shape, and most contain seasonal water and have bouldery floors.
To claim this cache: Answer the following questions, and post your answer in your log. Tell us how many people were in your group. (You don't have to wait for a confirmation from us to claim the cache. We trust you!)
Describe the appearance of the syenite erratic and compare it to the appearance of the many lighter colored bounders found along the trail. How are the two rocks types different? Take a photograph of yourself or your GPS receiver beside the imprisoned erratic.
The site is on the Northwestern flank of Kittatinny Mountain, 200 feet below the crest of Kittatinny Mountain. The local bedrock is the Shawangunk Formation (gray quartzite, and white quartz-pebble conglomerate of Silurian age), and bedding dips steeply northwest. The upper part of the mountain along its main ridge is characterized by many rock outcrops, weathered fractured rock, and very thin till. Most rock outcrops show evidence of glacial scour. They are striated and polished and exhibit a streamlined form. In this area the Ogdensburg-Culvers Gap moraine crosses the crest of Kittatinny Mountain and heads westward towards the Big Flat Brook valley; its course forming a large reentrant. The topography of the moraine lies in marked contrast to the glacially-scoured ridge crest of Kittatinny Mountain. The moraine, which lies about 100 feet below Sunrise Mountain Road, is an area of thick till characterized by ridge-and-swale and knob-and-kettle topography. Small boulder fields are common and most of the kettles contain seasonal water. This area of morainal topography provides diverse habitat for a wide variety of plants and animals in a very small area.
The recessional moraines in northwestern New Jersey are as much as 65 feet (20 m) thick, and 2500 feet (762 m) wide. Although, most are less than 1000 feet (305 m) wide. Their surfaces are bouldery, and they consist of poorly compacted stony till with minor beds of stratified sand, gravel, and silt. The moraines generally have asymmetrical cross sections and their distal slopes are the steepest. Their distal margins are sharp, whereas the innermost margins are indistinct. The outermost parts of the moraines are generally marked by single or parallel sets of ridges that are as much as 25 feet (8 m) high, 150 feet (46 m) wide, and 2000 feet (610 m) long. Although, most are less than 500 feet (152 m) long. Many appear to have been formerly continuous, but may have been disconnected by collapse during melting of buried ice. Sets of ridges are separated by elongated depressions that are as much as 20 feet (6 m) deep below their rim, 100 feet (30 m) wide, and 300 feet (91 m) long. The depressions parallel the ridges, and many contain swamp deposits. Irregularly-shaped depressions also occur, which are as much as 40 feet (12 m) deep, as much as 500 feet (152 m) wide, and probably were caused by melting of ice blocks. The innermost parts of the morainal segments have fewer ridges, fewer elongated depressions, and are marked by knob-and-kettle rather than ridge-and-kettle topography. The morphology expressed by the moraine at in the area of the Earthcache is typical for morainal segments that abut thick and widespread till. In general these segments are larger, more continuous, and have more fully developed moraine-parallel ridges than those abutting thin patchy drift.
The course of the moraines reflects both regional and local topographic control. Lines drawn perpendicular to their course parallel nearby striations, indicating ice was active at or very near the glacier margin. Well logs indicate that the Augusta moraine where it crosses Papakating Creek valley, and the Ogdensburg-Culvers Gap moraine, where it crosses the Paulins Kill and Wallkill Valleys overlie ice-contact deltaic outwash (Witte 1997) suggesting that these features were deposited following a readvance.
The lobate course of the moraines, their morphology, and evidence of glacial readvance suggests they were formed by 1) the transport of debris and debris-rich ice by the glacier at its margin, and 2) penecontemporaneous and postdepositional sorting and mixing of material by mass movement, chiefly resulting from slope failure caused by melting ice, and saturation and collapse of sediment. The source and mechanism of sediment transport is unclear. Most of the morainal material appears to be of local origin, but it is not known whether the glacier was reworking drift at its margin or transporting sediment to its margin by direct glacial action. Inwash is not a viable mechanism because the larger deposits lie on mountain or ridge tops. The origin of the moraine-parallel ridges is also unclear. These features may be push ridges. However, due to the absence of data on their internal structure, this premise is highly speculative.
Reference: Witte, Ron W (1998) Glacial Sediment and the Ice Age in New Jersey, New Jersey Geological Survey Information Circular.
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NEW JERSEY GEOLOGICAL SURVEY
an agency of the New Jersey Department of Environmental Protection.
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