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America's Volcanic Past
New Jersey

"Though few people in the United States may actually experience an erupting volcano, the evidence for earlier volcanism is preserved in many rocks of North America. Features seen in volcanic rocks only hours old are also present in ancient volcanic rocks, both at the surface and buried beneath younger deposits." -- Excerpt from: Brantley, 1994
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Map, Location of New Jersey

Volcanic Highlights and Features:
[NOTE: This list is just a sample of various New Jersey features or events and is by no means inclusive. All information presented here was gathered from other online websites and each excerpt is attributed back to the original source. Please use those sources in referencing any information on this webpage, and please visit those websites for more information on the Geology of New Jersey.]

  • New Jersey
  • New Jersey Regions
  • New Jersey Provinces - Brief Geologic History
  • New Jersey Counties with Volcanic Rocks
  • Byron Diabase
  • Cushetunk Mountain
  • Hook Mountain
  • Long Hill
  • Newark Basin
  • Orange Mountain Basalt
  • Patterson Falls
  • Riker Hill Park
  • Rocky Hill
  • Sourland Mountains
  • The Palisades
  • Wachung Mountains

New Jersey

New Jersey’s landscape has formed during more than a billion years of geologic processes such as mountain building, erosion and deposi­tion. This history has given the State distinctive landforms that are divided into four regions, known as phys­iographic provinces. Beginning in the northwest and proceeding southeast, these regions are called the Valley and Ridge, High­lands, Piedmont, and Coastal Plain Provinces. The first three are grouped with the larger classification known as the Appa­lachian Highland, the last with the Atlantic Slope. Both are major physiographic divisions of the United States.


Excerpt from:
New Jersey Geological Survey Website, 2004

   
New Jersey Regions

The Appalachian Highland:3
The Appalachians are old. A look at rocks exposed in today's Appalachian mountains reveals elongate belts of folded and thrust faulted marine sedimentary rocks, volcanic rocks and slivers of ancient ocean floor. Strong evidence that these rocks were deformed during plate collision. The birth of the Appalachian ranges, some 480 million years ago, marks the first of several mountain building plate collisions that culminated in the construction of the supercontinent Pangea with the Appalachians near the center.




The Atlantic Slope:3
The Atlantic Plain (Atlantic Slope) is the flattest of the provinces. It stretches over 2,200 miles in length from Cape Cod to the Mexican border and southward another 1000 miles to the Yucatan Peninsula. The Atlantic plain slopes gently seaward from the inland highlands in a series of terraces. This gentle slope continues far into the Atlantic and Gulf of Mexico, forming the continental shelf. This region was born during the breakup of the supercontinent Pangea in the early Mesozoic Era.


   
New Jersey Provinces - Brief Geologic History

New Jersey's Valley and Ridge Province:1,2
The Valley and Ridge Province, with an area of approxi­mately 536 square miles (about one-fifteenth of the State), occupies a major portion of Sussex and Warren Counties. This province, up to 17 miles wide, is characterized by steep-sided, linear ridges and broad valleys. It is under­lain by folded and faulted Paleozoic sedimentary rocks of Cambrian to Middle Devonian age (540 to 374 million years old) and minor amount of earliest Silurian-aged igneous rocks. Alternation of belts of erosion-resistant sandstone and easily-eroded shale and limestone creates the long, parallel northeast-southwest trending ridges and valleys characteristic of this province.

New Jersey's Highlands Province:1,2
The Highlands Province occupies an area of approximately 980 square miles, about one-eighth of the State. It lies within the southeastern portions of Sussex and Warren Counties, as well as major portions of Hunterdon, Morris, and Passaic and small parts of Bergen and Somerset. This moun­tainous belt is about 10 miles wide at the Delaware River and 25 miles wide near the New York border. In general its rugged topography consists of a series of discontinuous rounded ridges separated by deep narrow valleys. Although contiguous with the Reading Prong in Pennsylvania and the Hudson Highlands in New York, the use of the term “Highlands” (Rogers, 1840) for this region of New Jersey takes precedence. The Highlands are underlain predominantly by granite, gneiss, and small amounts of marble of Precambrian age. These rocks, the oldest in New Jersey, were formed between 1.3 billion and 750 million years ago by melting and recrystallization of sedimentary rocks that were deeply buried, subjected to high pressure and temperature, and intensely deformed. The Precambrian rocks are interrupted by several elongate northeast-southwest trending belts of folded Paleozoic sedimentary rocks equivalent to the rocks of the Valley and Ridge Province. The granites and gneisses are resistant to erosion and create a hilly upland dissected by the deep, steep-sided valleys of major streams. The belts of sedimentary rock form long, parallel ridges and valleys (for example, Bearfort Mountain, Long Valley, and the Musconetcong Valley) that extend through the province.

New Jersey's Piedmont Province:1,2
The Piedmont Province is an area of about 1,600 square miles and makes up approximately one-fifth of the state. It occupies all of Essex, Hudson, and Union Counties, most of Bergen, Hunterdon, and Somerset, and parts of Mercer, Middlesex, Morris, and Passaic. It is mainly underlain by slightly folded and faulted sedimentary rocks of Triassic and Jurassic age (240 to 140 million years old) and igneous rocks of Jurassic age. Highly folded and faulted lower Paleozoic sedimentary rocks along the northwestern margin in the Clinton and the Peapack areas, as well as at several smaller areas are included as part of the Piedmont. In the Trenton and Jersey City areas, along the southern margin of the province, there are small bands of highly metamorphosed rocks ranging in age from Middle Proterozoic to Cambrian that are also included.

Rocks of the Piedmont Province are separated from the rocks of the Highlands Province by a series of major faults, including the Ramapo Fault. The more resistant gneisses and granites on the upthrown northwest side of the faults make a prominent escarpment, 200 to 800 feet in height, extending from Mahwah through Boonton and Morristown to Gladstone, and from there westward in an irregular line to the Delaware River near Milford. South and east of this escarpment, interbedded sandstone, shale, conglomerate, basalt, and diabase of the Piedmont Province underlie a broad lowland interrupted by long, generally northeast-southwest trending ridges and uplands. The rocks of the Piedmont are of Late Triassic and Early Jurassic age (230 to 190 million years old). They rest on a large, elongate crustal block that dropped downward in the initial stages of the opening of the Atlantic Ocean -- one of a series of such blocks in eastern North America. These down-dropped blocks form valleys known as rift basins.

Volcanic activity was also associated with the rifting, as indicated by the basalt and diabase interlayered with the sandstone and shale. Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone. The basalt and diabase are extensively quarried for crushed stone.

New Jersey's Coastal Plain Province:1
By far the largest physiographic province in New Jersey is the Coastal Plain. With an area of 4,667 square miles occupying about three-fifths of the state, it includes all of Atlantic, Burlington, Camden, Cape May, Cumberland, Gloucester, Monmouth, Ocean, and Salem Counties and parts of Mercer and Middlesex. The unconsolidated deposits of the Coastal Plain dip gently to the southeast and range in age from the upper Lower Cretaceous to the Miocene (90 to 10 million years old). A broad trough follows the Piedmont boundary from the Raritan Bay to Trenton. Near Monmouth Junction, where the trough floor forms a saddle it reaches an elevation of about 80 feet. East of this depression is the drainage divide between the Delaware River and the Atlantic Ocean. The maximum elevation of the Coastal Plain, located at Crawford Hill, is 391 feet. The streams that flow northwest to the Delaware have narrow valleys, are shorter and have a steeper gradients than the streams that flow southeast. The Highlands of Navesink at 266 feet above sea level is the highest point directly on the coast.

   

New Jersey Counties with Volcanic Rocks

Bergen County:2
Outcrops of Jurassic basalt, western edge of Bergen County ...
Outcrops of Jurassic diabase, eastern edge of Bergen County ...
Outcrops of Precambrian gneiss or granite, northern tip of Bergen County

Essex County:2
Outcrops of Jurassic basalt, western Essex County

Hudson County:2
Outcrops of Jurassic diabase, central and eastern Hudson County

Hunterdon County:2
Small areas of outcropping of Jurassic basalt, northeast corner of Hunterdon County, and central Hunterdon County ...
Outcrops of Jurassic diabase, southern Hunterdon County and north central Hunterdon County ...
Outcrops of Precambrian gneiss or granite, northern Hunterdon County

Mercer County:2
Outcrops of Jurassic diabase, northern edge of Mercer County ...
Small area of Precambrian gneiss or granite, central Mercer County

Middlesex County:2
Outcrops of Jurassic diabase, west central Middlesex County

Morris County:2
Outcrops of Jurassic basalt, small sections of northeastern and southeastern Morris County ...
Outcrops of Precambrian gneiss or granite, western half of Morris County

Passaic County:2
Outcrops of Jurassic basalt, southeastern Passaic County ...
Outcrops of Precambrian gneiss or granite, western half of Passaic County

Somerset County:2
Outcrops of Jurassic basalt, northeast Somerset County ...
Outcrops of Jurassic diabase, southern tip of Somerset County ...
Outcrops of Precambrian gneiss or granite, northern tip of Somerset County

Sussex County:2
Outcrops of Precambrian gneiss or granite, eastern and southeastern Sussex County

Union County:2
Outcrops of Jurassic basalt, northwestern tip of Union County

Warren County:2
Outcrops of Precambrian gneiss or granite, southeastern Warren County




Byron Diabase

Byron Diabase:4
Exposures of a diabase sill crop out along Route 29 at Byron, New Jersey. The diabase is highly fractured, with joints filled with minerals including amphibole, calcite, epidote, and prehnite. The diabase intruded into the Lockatong Formation probably during the Early Jurassic when all the other volcanism occurred in the region.




Cushetunk Mountain

Cushetunk Mountain:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.




Hook Mountain

Hook Mountain:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.

Hook Mountain Basalt:4
The Hook Mountain Basalt stands out as the upper high wall of the quarry near the top of the hill. A thin, light-colored chill zone represents the effect of contact metamorphism in the sedimentary rock along the base of the lava flow. The basalt displays an abundance of vesicles, small vertical holes formed from gases venting from the lava before it cooled. The basalt in the quarry wall also displays poorly-developed columnar jointing. Some of these vesicles and fractures yield the pale green zeolite mineral, prehnite.




Long Hill

Long Hill:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.




Newark Basin

Newark Basin:4
The Newark Basin (in New Jersey, New York, and Pennsylvania) and the Connecticut River Basin are both "aborted rift" basins (rift basins that are no longer actively widening via rift-style tectonism and are no longer collecting sediments). Sediments began to accumulate in both basins during the Late Triassic. Both basins are half grabens which contain characteristic sedimentary conglomerates, sandstones, and mudrocks that usually bear a red or brownish appearance from an abundance of iron oxide minerals. ... Both the Newark and Connecticut River Basins contain "traprocks." The word, traprock, is derived from the Swedish word "trappa," meaning stair or step. In the mining usage, a traprock is any fine-grained igneous rock, ususally diabase or basalt, that can be crushed for building or road aggregate. Erosion creates their step-like appearance, producing abrupt termination of successive volcanic flows. During early Jurassic time, episodic rift-basin-style volcanism began to occur. Magma of basaltic composition migrated from the upper mantle to the surface along faults. Massive volcanic eruptions at the surface resulted in the formation of surface flows that spread for great distances across the low relief of the alluvial basins. After volcanism ended, the flows were buried beneath the more gradual accumulation of basin sediments. Because of the half-graben structure of these basin, the originally horizontal volcanic flows are now gently inclined. The resistance of traprocks to erosion (relative to the surrounding sandstone and shale) results in the formation gently dipping cuestas throughout the Mesozoic basins all along the Atlantic margin. Within the Newark Basin, the Watchung Mountains are examples of traprock questas. The ridges of resistant volcanic rock of the Palisades and the Watchung Mountains display steep escarpments on their eastern flanks and gentle slopes on their western flanks. This is an indication of the gentle dipping character of the strata towards the deeper western side of the basin. When the sediments were originally deposited there were probably nearly flat-lying. The structural dip of the rock probably developed as the basin continued to grow through time, even long after the youngest sediments of the basin were deposited.




Orange Mountain Basalt

Orange Mountain Basalt:4
Pillow lavas can be seen in the abandoned traprock quarries throughout the hillsides in the Paterson area. Minerals occur in fractures and in gas pockets that formed within the pillows of lava as they cooled. Some of the hollow chambers in the rock were probably lava tubes that drained before the lava cooled. The quarries in the Orange Mountain Basalt utilized the traprock primarily for construction material. Unfortunately, these quarries are closed to public access, but they are frequently the target of organized societal and college field trips. Mineral collecting within these quarries can be quite hazardous due to falling debris from the high walls, especially during the freeze-thaw cycles in the winter. Don't attempt to collect minerals without permission. If interested, be patient, and join a local mineral club or society on a trip.

Along Interstate 280:4
Driving westward along Interstate 280 the highway crosses the valley west of Newark ... the highway begins to ascend the grade rising to the ridge top of the 1st Watchung (Orange Mountain) ... The cliffs consist of a single massive lava flow that cooled and cracked into columnar joints. The unusual feature of this flow are the complexity of the columnar joints. In some locations, the joints tend to radiate away from a central core. These patterns were generated by an uneven cooling pattern in the flow, possibly a result of degassing structures or uneven mixing of the lava as it cooled.




Patterson Falls

Patterson Falls:4
The falls spill over a resistant ridge into a chasm carved in the lower flow of the Orange Mountain Basalt where it overlies the upper contact of the Passaic Formation. In the vicinity of the falls, glacial erosion has stripped away the upper more friable pillow lavas. These pillow lavas can be seen in the abandoned traprock quarries throughout the hillsides in the Paterson area. Minerals occur in fractures and in gas pockets that formed within the pillows of lava as they cooled. Some of the hollow chambers in the rock were probably lava tubes that drained before the lava cooled. The quarries in the Orange Mountain Basalt utilized the traprock primarily for construction material. Unfortunately, these quarries are closed to public access, but they are frequently the target of organized societal and college field trips. Mineral collecting within these quarries can be quite hazardous due to falling debris from the high walls, especially during the freeze-thaw cycles in the winter. Don't attempt to collect minerals without permission. If interested, be patient, and join a local mineral club or society on a trip.




Riker Hill Park

Riker Hill Park:4
Riker Hill Park is an excellent location to examine fresh exposures of sedimentary red beds and basalt typical of the Newark Basin region. The park is located along the western side of the Newark Basin near Rosedale, New Jersey, close to the intersection of Interstate 280 with Interstate 287.

Hook Mountain Basalt:4
The Hook Mountain Basalt stands out as the upper high wall of the quarry near the top of the hill. A thin, light-colored chill zone represents the effect of contact metamorphism in the sedimentary rock along the base of the lava flow. The basalt displays an abundance of vesicles, small vertical holes formed from gases venting from the lava before it cooled. The basalt in the quarry wall also displays poorly-developed columnar jointing. Some of these vesicles and fractures yield the pale green zeolite mineral, prehnite.




Rocky Hill

Rocky Hill:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.




Sourland Mountains

Sourland Mountains:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.




The Palisades

The Palisades:4
The Palisades were designated a "National Natural Landmark" being "the best example of a thick diabase sill in the United States." The sill extends southward beyond the cliffs in Jersey City beneath the Inner Harbor, and reappear on Staten Island. The Palisades are the eroded cross-section of a large intrusive diabase sill that intruded between layers of sandstone and shale of the Late Triassic Stockton and Lockatong Formations. (In the Staten Island area, the strata equivalent to the Lockatong Formation is called the Brunswick Formation.) The sill approaches 1,000 feet thick and was probably fed from an unknown stock buried beneath the basin to the west. Radiometric age determinations of the diabase suggest that the sill formed in multiple stages between about 192 to 186 million years ago (late Early Jurassic).

Olivine Layer:4
Within the lower portion of the sill there is a zone of rock enriched in olivine, a high temperature ultramafic mineral that formed first and settled to the bottom of the intrusion before the rest of the magma cooled. This zone is about 10 to 15 feet thick, and crops out along and above the road in the Ross Dock area near the south entrance to the park.

The Palisades Diabase:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.

The Palisades and the Lincoln Tunnel:4
An outcrop of diabase at the top of the cliffs is one of the first thing you see when you emerge onto the ramp from the Lincoln Tunnel on the New Jersey end.




Wachung Mountains

Wachung Mountains:2
Diabase is a rock formed by the cooling of magma at some depth in the crust; basalt is formed by cooling of an identical magma that has been extruded onto the surface as lava. Both basalt and diabase are more resistant to erosion than the enclosing sandstone and shale and therefore they form ridges and uplands. The Palisades, Rocky Hill, Sourland Mountains, and Cushetunk Mountain are underlain by diabase layers. The Watchung Mountains, Long Hill, and Hook Mountain are underlain by basalt layers. Valleys and lowland between these ridges are underlain by shale and sandstone.

Along Interstate 280:4
Driving westward along Interstate 280 the highway crosses the valley west of Newark ... the highway begins to ascend the grade rising to the ridge top of the 1st Watchung (Orange Mountain) ... The cliffs consist of a single massive lava flow that cooled and cracked into columnar joints. The unusual feature of this flow are the complexity of the columnar joints. In some locations, the joints tend to radiate away from a central core. These patterns were generated by an uneven cooling pattern in the flow, possibly a result of degassing structures or uneven mixing of the lava as it cooled.

Wachung Reservation:4
The Watchung Reservation is a nature preserve encompasses 2,000 acres straddling portions of the 1st and 2nd Watchung Mountains to the south and west of the Milburn near Scotch Plains, New Jersey. There are a variety of locations in the area worth examining, including exposures of Early Jurassic red beds and basalt flows.




Excerpts from:
1) New Jersey Geological Survey Website, 2004
2) Geologic Map of New Jersey, 1999: New Jersey Geological Survey, Department of Environmental Protection, Division of Science, Research and Technology
3) USGS/NPS Geology in the Parks Website, 2001
4) Stoffer, Phil, 2003, Geology of the New York City Region, A Preliminary Regional Field-Trip Guidebook: U.S. Geological Survey Website, 2004.

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09/08/04, Lyn Topinka