America's Volcanic Past
|"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|
Volcanic Highlights and Features:
|[NOTE: This list is just a sample of various New York 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 York.]|
The most common types of rock in New York are the
shale and siltstone, sandstone, limestone and dolostone.
The oldest rock in the State is
tonalite, an igneous rock, now
found in the southeast Adirondacks, is dated at
1,300 million years old (1.3 billion years old).
Excerpt from: New York State Geological Survey Website, 2001
The Interior Plains:3
The Interior Plains is a vast region that spreads across the stable core (craton) of North America. This area had formed when several small continents collided and welded together well over a billion years ago, during the Precambrian. Precambrian metamorphic and igneous rocks now form the basement of the Interior Plains and make up the stable nucleus of North America. With the exception of the Black Hills of South Dakota, the entire region has low relief, reflecting more than 500 million years of relative tectonic stability.
The Atlantic Plain:3
The Atlantic Plain 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 York's Volcanic Rocks|
New York's Granite Mines:2
Clinton, Essex, Franklin, Jefferson, Oneida, St. Lawrence, and Washington Counties (northeastern New York) have operating granite mines.
New York's Oldest Rock - Tonalite:1
The oldest rock in the State is tonalite, an igneous rock, now metamorphosed, found in the southeast Adirondacks, is dated at 1,300 million years old (1.3 billion years old).
New York's Traprock Quarries:2
Rockland and Westchester Counties (southeastern New York) have operating traprock quarries.
New York's Wollastonite Mines:2
Wollastonite is a white fibrous calcium silicate mineral (CaSiO3) created by highly metamorphosed sandy limestones intruded by magma. It was mined as early as 1810 near Willsboro in Essex County, New York. Over 99 percent of the wollastonite produced in the United States comes from New York. A mineral with a needle-like structure, its qualities of durability, moisture-resistance and color-fast brilliant whiteness make it suitable for a wide variety of uses from dental cleaning, to car bumpers, to vinyl floor tiles. Wollastonite is used in the following industries: ceramic, plastic, automotive, construction, paint and coatings, frictions and metallurgical. Wollastonite is also the stuff in the match heads that makes them burn evenly. Essex and Lewis Counties (northern New York) have operating wollastonite mines.
|New York's Garnet Deposits|
New York's Garnet Deposits:5
Deposits of industrial garnet are found at two locations in New York. In the Gore Mountain area, industrial garnet is mined as the primary product; and near the town of Willsboro, byproduct of it is recovered as wollastonite mining. The deposit near Gore Mountain is an almandite-bearing diorite of uncertain, igneous or metamorphic origin. The garnet is present as imperfectly developed crystals surrounded by a rim of coarsely crystalline hornblende. The crystals range from about 1 millimeter to almost 1 meter in diameter but average about 100 millimeters in diameter. The garnet has a pronounced laminated structure, which enables it to naturally break into thin plates from about 2 to 6 millimeters in thickness. Garnet fragments maintain this platy particle shape even as they are crushed smaller and smaller. These same deposits in Warren County contain good to fine quality facet-grade garnets. The garnet is a solid solution of pyrope-almandite-grossularite that results in a pleasant deep brownish-red material which often has an orange cast. Beautiful small stones can be cut, but larger stones are too dark to be attractive.
New York State and the Adirondack Mountains:4
The Adirondack Mountains form most of northern New York state. They are an uplifted complex of Precambrian metamorphic rocks - like the Llano Uplift in Texas, a part of an ancient (Grenville) continental province. The Paleozoic sedimentary strata that now flank these older rocks once covered them. The intersecting faults and joints responsible for the rectilinear surface texture of the Precambrian rocks developed from release of pressure on this once deeply buried metamorphic complex.
Igneous and metamorphic rocks make up the Adirondacks and Hudson Highlands.
New York State and the Appalachian Mountains:4
Alternating beds of hard and soft Paleozoic sedimentary rocks, folded like the wrinkles in a kicked floor rug, are the hallmark of the Appalachian Valley and Ridge Province. Extending some 900 miles (1,500 kilometers) from New York to Alabama, and flanked by flat-lying sedimentary strata to the west and Precambrian metamorphic rocks to the east, this famous belt of parallel structures reflects the several great continental collisions that formed the Appalachian chain and the Pangea supercontinent some 300 to 400 million years ago.
|Bear Mountain State Park|
Bear Mountain State Park:6
The bedrock throughout Bear Mountain State Park is the Storm King Granite (Late Proterozoic), a fairly uniform granite gneiss cut with occasional quartz-filled veins, migmitite, and pegmatite dikes. In the valleys and hillsides to the north and south of Bear Mountain are a number of iron mines which extracted magnetite ore from hornblendite gabbro veins.
Central Park occupies an area of 840 acres and extends between 59th and 110th streets between 5th Avenue (Central Park East) and 8th Avenue (Central Park West). The park is considered one of the greatest achievements in artificial urban landscaping. Most of the park land was purchased in 1856 at a price of $5,000,000. The layout was designed by Frederick Law Olmstead and Calver Vaux to, in part, "preserve and enhance" the natural features of the terrain. Construction of the park took twenty years, and involved the draining of swamps, planting of trees, contouring the landscape, and the importation of soil of good quality to cover the existing poor, rocky alluvium. Central Park was officially opened in 1876.
Central Park Gneiss:6
Central Park is a popular site for geology field trips in the New York City area, and for good reason. The park is extremely accessible and is close to many museums, including the American Museum of Natural History (79th and Central Park West). Exposures of the Cambrian Manhattan Formation (or Manhattan Schist) crop out throughout the park, particularly throughout its southern end. Features of geologic interest include a variety of metamorphic rock features, glacial features, and the urban setting of the park itself. The best way to examine the geology is to plan a circuit walk around the south and central portions of the park. Large outcrops of crenulated schist and gneiss are scattered throughout the tailored landscape. Many of the exposures preserve glacially-polished surfaces, striations, and grooves carved from rocks embedded in the base of the ice sheet as it moved southward.
Diabase Glacial Erratics:6
Although most of the glacial erratics have been removed, some remain scattered among the undeveloped portions of the park, particularly on many of the large barren exposures of bedrock and around the park ponds. Some have been incorporated into garden walls and bridges within the park. Most erratics are pieces of the Cambrian Manhattan Formation derived from sources nearby, whereas others have been transported much greater distances. The most obvious are large, dark boulders of diabase derived from the Palisades Sill of Jurassic age which crops out along the western side of the Hudson River.
Igneous and metamorphic rocks make up the Adirondacks and Hudson Highlands.
Rocks of the Hudson Highlands:1
Middle Proterozoic Age (1.3 to 1.0 billion years old):
|New York City|
Just east of the main entrance to the New York Botanical Gardens there are several large rocky exposures of Fordham Gneiss. Outside the entrance to the "Native Plant and Rock Garden" area is an unusual large gneiss boulder, an erratic, which has been broken in half. The boulder was probably split by the growth of a tree within a small crack. As the tree grew, its roots eventually wedged the boulder into pieces, but the tree has long-since vanished. A walk along Azalea Way affords views of barren rock hills of Fordham Gneiss among the parkland's forest. Paths follow along the Bronx River and between botanical theme exhibits throughout the park.
Crotona Park is on the south side of the Cross Bronx Expressway at Exit 3. The park is in a Bronx neighborhood that has witnessed significant urban development in recent years. Numerous exposures of schist and gneiss of Cambrian Manhattan Formation are present throughout the park, many of which bear glacial polish, striations, and groves. Crotona Avenue extends northward from the Park to Fordham Road. Just east of Crotona Avenue, Fordham Road is the boundary between the New York Botanical Gardens and the Bronx Zoological Park.
Inwood Hill Park:6
Inwood Hill Park consists of a number of playing fields on its eastern side, with a forested, rocky upland on its western margin. The park is bordered by the Husdon River to the west, the Harlem River to the north, by Seaman Avenue and Payson Street to the east, and by Dyckman Street to the south. The steep hillsides along the western edge of Inwood Park are host to large outcrops of the Manhattan Formation. The formation consists of gray, garnetiferous schist and dark-colored amphibolite gneiss. Outcrops of schist and gneiss bearing garnet crystals up to an inch in diameter occur along the trail directly west of the intersection of Isham Avenue with Seaman Avenue around the baseball fields. A trail system leads upward through a beautiful climax forest to high points overlooking the Harlem River. This area was the last portion of Manhattan to be developed. Until as recently as the 1940s the Inwood Park was still farmland and the home of a small village of Native Americans.
Pelham Bay Park:6
The park encompasses 2,764 acres of coastal lowland, of which roughly a quarter is set aside as two wildlife sanctuaries. The Thomas Pell Wildlife Sanctuary along the Hutchinson River/Eastchester Bay side of the park and is host to tidal marshes bordered by oak-hickory forests. The Hunter Island Marine Zoology and Geology Sanctuary is on the north side of the Orchard Beach bathing area, and includes the northeastern shoreline of Hunter Island, and all of Twin Islands, Two Trees Island, and Cat Briar Island. Storm waves from Long Island Sound have eroded the coastline along Hunter Island, exposing the bedrock of Hartland Formation. The rock consists of granitic and garnetiferous amphibolite gneiss with numerous quartz veins and migmatite dikes. Migmatite is an type igneous rock that forms when metamorphic rocks begin to melt under high temperature. Felsic minerals melt and are injected into the surrounding rock along joints, faults, and other zones of weakness in the rock. As the igneous material gradually cools, bands of feldspar and quartz crystals form along the edges of the intrusion. The center of the migmatite veins typically consist of larger crystals of feldspar and quartz. The migmatite stands out in outcrops as light-colored bands in contrast to the darker amphibolite gneiss host rock. In some cases, the dikes cut across older dikes and quartz-filled veins; many are folded or display offset by faulting. Overlying the bedrock is a blanket of glacial till from which numerous erratics are weathering. The beach is littered with large erratics derived from bedrock sources nearby.
Fragments of Palisades Diabase can be found practically everywhere in glacial and shore gravel deposits in Manhattan, Brooklyn, Queens, and Staten Island.
Todt Hill, Staten Island:6
Todt Hill on Staten Island is the highest point along the Atlantic Seaboard south of Maine. The highest point, 410 feet above sea level, is located just south of the intersection of Todt Hill Road with Ocean Terrace. "Todt" is a Dutch word meaning "dead." This hill probably received its name from the Dutch settlers because the hilltops overlooking the Verrazano Narrows consisted of scattered treeless rocky exposures. The chemical character of the bedrock was, in part, the reason for this. Much of Staten Island is covered by the Harbor Hill moraine, the terminal moraine of the last Wisconsin Stage glacier. However, ledges of bedrock consisting of serpentinite are exposed throughout the upland areas on Staten Island. Serpentine, the dominant mineral in serpentinite, is rich in magnesium, an element that most plants cannot tolerate in high concentrations. The enrichment of magnesium in the thin soil covering the glacier-scoured hilltops is probably responsible for the original barren exposures on Todt Hill. The serpentinite has a bluish to greenish gray color, and consists of serpentine (mostly the variety antigorite), with accessory minerals of chrysotile (a form of asbestos), magnetite, and talc. Serpentinite is derived by the metamorphism of ultramafic rocks (rocks rich in the minerals olivine and pyroxene) in a water-rich environment. The probable original setting for these rocks was within the igneous crust beneath the Iapetus Ocean. The occurrence of serpentinite in the core of Staten Island is an indication that the allochtohonous basement rocks consisting of oceanic crustal material were thrust landward onto the eastern margin of the continent during the Taconic Orogeny. The occurrence of serpentinite is consistent with the interpretation that Staten Island is east of Cameron's Line
1) New York State Geological Survey Website, 2001
2) New York State Department of Environmental Conservation Website, 2001
3) USGS/NPS Geology in the Parks Website, 2001
4) USGS A Tapestry of Time and Terrain Website, 2002
5) Gemstones, An Overview of Production of Specific U.S. Gemstones: U.S. Bureau of Mines Special Publication 14-95
6) 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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