The Watchung Outliers include six areas of isolated low hills and rock
outcrop
An outcrop or rocky outcrop is a visible exposure of bedrock or ancient superficial deposits on the surface of the Earth.
Features
Outcrops do not cover the majority of the Earth's land surface because in most places the bedrock or superficia ...
s of
volcanic
A volcano is a rupture in the crust of a planetary-mass object, such as Earth, that allows hot lava, volcanic ash, and gases to escape from a magma chamber below the surface.
On Earth, volcanoes are most often found where tectonic plates a ...
and
sedimentary
Sedimentary rocks are types of rock that are formed by the accumulation or deposition of mineral or organic particles at Earth's surface, followed by cementation. Sedimentation is the collective name for processes that cause these particles ...
origin in the U.S. states of
New York,
New Jersey
New Jersey is a state in the Mid-Atlantic and Northeastern regions of the United States. It is bordered on the north and east by the state of New York; on the east, southeast, and south by the Atlantic Ocean; on the west by the Delaware ...
, and
Pennsylvania
Pennsylvania (; ( Pennsylvania Dutch: )), officially the Commonwealth of Pennsylvania, is a state spanning the Mid-Atlantic, Northeastern, Appalachian, and Great Lakes regions of the United States. It borders Delaware to its southeast, ...
. These geologic
outliers are primarily diminutive and detached remnants of the
Triassic
The Triassic ( ) is a geologic period and system (stratigraphy), system which spans 50.6 million years from the end of the Permian Period 251.902 million years ago (Year#Abbreviations yr and ya, Mya), to the beginning of the Jurassic Period 201.36 ...
/
Jurassic
The Jurassic ( ) is a geologic period and stratigraphic system that spanned from the end of the Triassic Period million years ago (Mya) to the beginning of the Cretaceous Period, approximately Mya. The Jurassic constitutes the middle period of ...
age
Watchung Mountain basalt flows with intervening layers of sedimentary rock. All six of the outliers are found along the western edge of the
Newark Basin
The Newark Basin is a sediment-filled rift basin located mainly in northern New Jersey but also stretching into south-eastern Pennsylvania and southern New York. It is part of the system of Eastern North America Rift Basins.
Geology
Approximat ...
, occupying small
synclines adjacent to the
Ramapo fault system. The outliers, from north to south, are known as: Ladentown, Union Hill, New Germantown/Oldwick (including Round Top), Prospect Hill, Sand Brook, and Jacksonwald.
Ladentown Outlier
The Ladentown Outlier is the most northern of the Watchung Outliers, located along the border of the
Town of Haverstraw and
Ramapo, New York
Ramapo is a town in Rockland County, New York, United States. It was originally formed as New Hampstead, in 1791, and became Ramapo in 1828."Ramapo", in Peter R. Eisenstadt and Laura-Eve Moss (Eds.), The Encyclopedia of New York State'. Syr ...
, approximately seven miles north of the maximum extent of the Watchung Mountains at
Campgaw Mountain
Campgaw Mountain is the northernmost ridge of the volcanically formed Watchung Mountains, along the border of Franklin Lakes, Oakland, and Mahwah in Bergen County, New Jersey, United States. Located almost entirely within the bounds of Ca ...
. The outlier is completely composed of volcanic
trap rock
Trap rock, also known as either trapp or trap, is any dark-colored, fine-grained, non-granitic intrusive or extrusive igneous rock. Types of trap rock include basalt, peridotite, diabase, and gabbro.Neuendorf, K.K.E., J.P. Mehl, Jr., and J.A. ...
, the Ladentown basalt, which covers a considerable area, running at or beneath the surface for a length of about two miles with a width of about a mile.
Originally, because of its close proximity to the
Palisades, the Ladentown basalt was thought to be an extension of the intrusive sill. It is now known from magnetic and gravity measurements that the Ladentown basalt is linked to the Palisades by a significant subsurface volcanic dike,
[Kodama, K.P., 1983. Magnetic and gravity evidence for a subsurface connection between the Palisades sill and the Ladentown basalts. ''Geological Society of America Bulletin'', v. 94, no. 1, p. 151–158.] but it is definitely an extrusive feature, displaying Orange Mountain Basalt characteristic of First Watchung Mountain.
[Olsen, P.E., 1980. The Latest Triassic and Early Jurassic Formations of the Newark Basin (Eastern North America, Newark Supergroup): Stratigraphy, Structure, and Correlation. ''New Jersey Academy of Science Bulletin'', v. 25, no. 2, p. 25–51.] This makes the Ladentown basalt unique among the Watchung basalts in that it appears to be rooted to an intrusive feature. In this respect, the Ladentown basalt can be thought of as the remains of a
fissure volcano, owing to the extrusion's slab-like character and ramping profile. New research indicates that the vicinity of Ladentown may have served as the primary vent from which the magma of the
Palisades Sill
The Palisades Sill is a Triassic, 200 Ma diabase intrusion. It extends through portions of New York and New Jersey. It is most noteworthy for The Palisades, the cliffs that rise steeply above the western bank of the Hudson River. The ideal loc ...
erupted to the surface to form the Watchung flood basalts.
[Puffer, J.H., Block, K.A., Steiner, J.C., 2009. Transmission of Flood Basalts through a Shallow Crustal Sill and the Correlation of Sill Layers with Extrusive Flows: The Palisades Intrusive System and the Basalts of the Newark Basin, New Jersey, U.S.A. ''The Journal of Geology'', volume 117, p. 139–155.]
Union Hill
Union Hill is located near the village of
Suffern in
Ramapo, New York
Ramapo is a town in Rockland County, New York, United States. It was originally formed as New Hampstead, in 1791, and became Ramapo in 1828."Ramapo", in Peter R. Eisenstadt and Laura-Eve Moss (Eds.), The Encyclopedia of New York State'. Syr ...
, about three and a half miles north of the Watchung Mountains, or about halfway between the Ladentown Outlier and Campgaw Mountain. The hill, primarily composed of trap rock, originally rose 150 feet above the surrounding terrain,
[Darton, Nelson Horatio. ''Bulletin of the United States Geological Survey No. 67 – The Relations of the Traps of the Newark System in the New Jersey Region''. Government Printing Office, Washington, 1890. See Pages 53, Union Hill Trap.]
Available via Google Books
/ref> but extensive quarrying has since obliterated most of the hill except for the slopes of its perimeter. Like the Ladentown Outlier, Union Hill was once considered to be an extension of the Palisades. It was determined later in the 20th century that the hill was composed of extrusive basalt with a minimum thickness of 125 ft (38 m). However, by 2011 it was known that the outlier, once considered to consist only of a single type of basalt, is more complex than originally thought. The outermost part of the outlier is composed of an elongated arc of Orange Mountain Basalt. Lying within this arc and stratigraphically above it is a band of sedimentary rock from the Feltville Formation. Finally, lying within and above the band of sedimentary rock is a central area of Preakness Mountain Basalt which constitutes the portion of the outlier reduced by quarrying.[Volkert, Richard A. ''Bedrock Geological Map of the Ramsey Quadrangle, Passaic and Bergen Counties, New Jersey and Rockland County, New York – Open File Map OFM 87''. New Jersey Geological Survey, 2011.]
Available Online
/ref>
New Germantown Outlier
The New Germantown Outlier (also known as the Oldwick Outlier) is the most northern of the outliers south of the Watchung Mountains. The hills of the New Germantown Outlier are located along the border of Tewksbury Township and Readington Township, New Jersey
Readington Township is a township located in the easternmost portion of Hunterdon County, New Jersey, United States. As of the 2010 United States Census, the township's population was 16,126, reflecting an increase of 323 (+2.0%) from the 15,803 ...
, approximately seven miles southwest of the southern extent of the Watchungs and about three miles north of Cushetunk Mountain.
The structure of the New Germantown Outlier appears to mirror the construction of the Watchung Mountains on a tiny scale. The eastern side of the feature consists of a horseshoe shaped ridge with prongs facing to the west. This ridge is composed of Orange Mountain (First Watchung Mountain) basalt which is actively quarried. West of this First Watchung-like ridge is a valley occupied by sedimentary layers of the Feltville Formation, characteristic of the valley between the First and Second ridges of the Watchungs. Finally, at the center of the horseshoe is a dome of volcanic rock forming a hill known as Round Top. The hill is composed of Preakness Mountain Basalt, making it the equivalent of Second Watchung Mountain in the New Germantown complex.[Mineral Resources Online Spatial Data – Preakness Basalt](_blank)
U.S. Geological Survey. Accessed December 22, 2009. The thickness of basalt in this outlier is estimated at close to 425 ft (~130 m).
Prospect Hill
Located along the border of western Flemington and Raritan Township, New Jersey
Raritan Township is a township in Hunterdon County, New Jersey, United States. As of the 2010 United States Census, the township's population was 22,185, reflecting an increase of 2,376 (+12.0%) from the 19,809 counted in the 2000 Census, whi ...
, Prospect Hill constitutes the smallest of the Watchung Outliers, being approximately one fourth of a mile wide and extending north to south for less than half a mile.[Darton, Nelson Horatio. ''Bulletin of the United States Geological Survey No. 67 – The Relations of the Traps of the Newark System in the New Jersey Region''. Government Printing Office, Washington, 1890. See Page 66.]
Available via Google Books
/ref> The hill is composed of Orange Mountain Basalt, with no overlying Jurassic sediments apparent. Dikes branching south from the vicinity of the outlier appear to be connected to the intrusive igneous Sourland Mountain
Sourland Mountain is a long ridge in central New Jersey, extending from the Delaware River at Lambertville to the western end of Hillsborough Township near the community of Neshanic, through Montgomery Township and into Hopewell Township ...
, an extension of the Palisades Sill
The Palisades Sill is a Triassic, 200 Ma diabase intrusion. It extends through portions of New York and New Jersey. It is most noteworthy for The Palisades, the cliffs that rise steeply above the western bank of the Hudson River. The ideal loc ...
.[Lewis, Volney J. ''Annual Report of the State Geologist of New Jersey for the Year 1907 – Part IV: Petrography of the Newark Igneous Rocks of New Jersey''. John L. Murphy Publishing Company, Printers, Trenton, NJ, 1908. See Pages 166–167'']
Available via Google Books
[Kümmel, Henry B. ''Annual Report of the State Geologist of New Jersey for the Year 1897 – Part II: The Newark System''. John L. Murphy Publishing Company, Printers, Trenton, NJ, 1898. See Pages 92–93'']
Available via Google Books
In this respect, Prospect Hill likely marks another location where the Palisades magma found a way to the surface, albeit not as significant as in the Ladentown Outlier.
Sand Brook Outlier
The Sand Brook Outlier, located in the eastern part of Delaware Township, New Jersey, appears nearly identical in construction to the New Germantown Outlier. A low ridge composed of Orange Mountain Basalt forms a horseshoe around the eastern edge of a belt of sedimentary strata from the Feltville Formation. In the middle of the outlier is a dome-like structure of what is likely Preakness Mountain Basalt, not unlike Round Top in the New Germantown complex. The thickness of the basalt in this outlier is estimated at nearly 400 ft (~120 m), similar to New Germantown.
Jacksonwald Outlier
The Jacksonwald Outlier is the only Watchung Outlier in Pennsylvania. It is located over 100 km southwest of the actual Watchung Mountains in Exeter Township. The outlier shares some similarity with the Sand Brook and New Germantown outliers. As in the other two outliers, the Jacksonwald Outlier features a low, horseshoe shaped ridge of Orange Mountain Basalt (sometimes referred to as just the Jacksonwald Basalt) that embraces an area composed of sedimentary strata from the Feltville Formation. However, unlike in the Sand Brook and New Germantown outliers, the Jacksonwald Outlier lacks a central dome of Preakness Mountain Basalt. The thickness of the basalt in this outlier is estimated to be in excess of 325 ft (~100 m).
An interesting trait of the Jacksonwald Outlier is that it is surrounded by a ridge of intrusive diabase on its eastern side. The diabase, which lies stratagraphically below the basalt, is thought to have been intruded into the syncline containing the Jacksonwald Outlier during or after some degree of folding had affected local strata. The diabase is therefore considered to constitute a phacolith
A phacolith is a pluton of igneous rock parallel to the bedding plane or foliation of folded country rock. More specifically, it is a typically lens-shaped pluton that occupies either the crest of an anticline or the trough of a syncline. In ra ...
.[LeTourneau, Peter M. & Olsen, Paul E. (editors). “The Great Rift Valleys of Pangea in Eastern North America – Volume One: Tectonics Structure and Volcanism”. Columbia University Press, New York, 2003. . See Page 41. ]
Limited Preview available via Google Books
See also
*Watchung Mountains
The Watchung Mountains (once called the Blue Hills) are a group of three long low ridges of volcanic origin, between high, lying parallel to each other in northern New Jersey in the United States. The name is derived from the American Native Lena ...
References
External links
Geocaching.com – Two Hundred Million Year-Old Lava Flow!
Earthcache at the base of Prospect Hill described by the New Jersey Geological Survey.
{{coord, 40.511, -74.866, type:landmark_globe:earth_region:US-NJ, display=title
Triassic volcanism
Jurassic volcanism
Volcanism of New Jersey
Volcanism of New York (state)
Volcanism of Pennsylvania
Watchung Mountains
Mountains of New Jersey
Ridges of New Jersey
Mountain ranges of New Jersey
Mountains of Pennsylvania
Mountains of New York (state)