New York City, New York
New York City is home to some of the world’s most important financial institutions, well-known museums, and was the original site where architects and engineers anchored the world’s tallest buildings into bedrock. With all its skyscrapers, paved streets, and subway tunnels, New York City would seem to be the last place to study bedrock geology, but in the past, the city’s rocky floor was one of the most exposed and excavated in the United States. Remnants of the rocky hills and valleys are well displayed in Central and Inwood Hill parks. More typically, the relatively rugged, pre-colonial topography has been leveled by excavation of the hills and filling of the lowlands. The excavations for the subway system, buildings, underground railroads, water tunnels, and so on, uncovered the rocks beneath New York City to the delight of both geologists and mineral collectors. New York City’s administrative divisions (boroughs) overlap six different geological domains. Each of them contains specific rocks, and rock-forming minerals.
The rocks beneath New York City record more than 1 billion years of geological history from the Proterozoic to present. They “witnessed” through geological time both the assembly and break-up of two supercontinents, Rodinia and Pangea, and their associated metamorphic and igneous processes.
Proterozoic assembly of Rodinia:
Formed during the Grenville Orogenic Cycle, as part of the Rodinia supercontinent, the Fordham Gneiss is the oldest rock, 1.17 Ga (Aleinikoff 1985), of the New York City basement. It crops out in the Bronx, extends into Manhattan and is covered by Mesozoic sedimentary rocks in Queens and Brooklyn. The Fordham Gneiss consists of interlayered felsic to mafic metaigneous (plutonic and volcanic) and metasedimentary rocks. Northern Bronx is underlain by the Yonkers Gneiss. This gneiss grades into more mica-rich metamorphic rocks (schists), and both are apparently old volcanic rocks that have ages of 563 and 570 Ma. The Cambrian Lowerre Quartzite unconformably overlies the Proterozoic units in Bronx.
Many millions years ago, sediments were deposited into a shallow sea that covered the eastern part of proto-North America (Laurentia). During the Taconic Orogeny (about 450 Ma) an island arc - similar to the present day Japanese archipelago - moved toward and collided with the continent. For the duration of the collision, a sequence of rocks, hartzburgites and dunites, were “grabbed” from the floor (oceanic crust) of the ancient Iapetus Ocean, the ocean between the proto-North America and the Taconic arc, and were pushed (obducted) onto the continent. These shallow sea sediments were metamorphosed to amphibolite facies during the collision and formed the Manhattan schists. The oceanic crust rocks were also subjected to low-grade metamorphism and were transformed into serpentinite. That was the first stage in the formation of the new supercontinent Pangea.
The Cambrian Manhattan schists that contain the Manhattan and Hartland formations, underlay Manhattan Island with a slight extension into the Bronx; they consist of strongly deformed quartz-plagioclase-biotite ± garnet, kyanite, sillimanite, and amphibole schists, leucocratic metamorphic differentiates, amphibole schists, and cross-cutting pegmatite dikes or lenses. A tectonic boundary, Cameron’s line, is suggested to separate the Hartland Formation from the Manhattan Schists. Whether the Manhattan Schists and Hartland Formations represent different geological environments is still a matter of debate.
The Inwood marble is a sacccharoidal textured calcitic-dolomitic ± tremolite, phlogopite, chlorite, and garnet marble, often silica-rich. This carbonate sequence overlies the Lowerre Quartzite in the Bronx and with a small extension into Manhattan. It was deposited on a stable continental shelf during the Cambrian to Early Ordovician. The Late Ordovician Walloomsac Formation which includes interbedded black schists and marble overlies the Inwood Marble.
The mid-Ordovician serpentinite occurs in the southeastern part of Staten Island. The serpentinite has a bluish to greenish gray color, and consists of serpentine (mostly the species antigorite), with accessory minerals chrysotile (a form of asbestos), magnetite, and talc. The serpentinite often has a boxwork texture, peppered in places with isometric grains of chromite, and cross-cut by narrow veins of calcite.
As Pangaea split apart during the Mesozoic era, the Atlantic Ocean began opening at around 199 Ma. Due to the tensional stress produced by the opening of the new ocean, the Newark basin and a series of other sedimentary basins developed along the eastern coast of North America. Material eroded from higher elevations was deposited into these basins during the Triassic and Early Jurassic and these sediments were later hardened into rock. Some of the Triassic rocks of the Newark Basin occur in the northwestern part of the Staten Island: (1) sandstones and arkoses (the Stockton Formation); (2) siltstones and shales (the Lockatong Formation); and (3) shales, siltstones, sandstones, and conglomerates (the Passaic Formation).
During the Cretaceous Period (136–65 Ma), sands and muds eroded from the higher areas of the region were deposited to form the coastal plain sediments of the Raritan and Magothy formations in northwestern Staten Island. The old quarries dug in these formations for brick clay yielded early flowering plant fossils in the late 1800s.
The Palisades Sill of west-central Staten Island is "the best example of a thick diabase sill in the United States" (http://3dparks.wr.usgs.gov/nyc/parks/loc39.htm). It was intruded between 192 and 186 million years ago into the sedimentary rocks of the Lockatong and Stockton formations. The rock is medium to dark gray in fresh hand specimens and consists mainly of pyroxene and plagioclase.
The ice sheet of the Wisconsinan Stage covered almost the entirety of New York State extending southeastward onto Long Island. One major effect of the movement of the ice sheet was the erosion and sculpting of bedrock in New York City. For example, many of the bedrock hills in Central Park are aligned roughly N–S, with gentle slopes that slope up to the south at their north end and with abrupt southern slopes. These are called “roches moutonees” (or sheep rocks), and were produced by the grinding of sand, pebbles and boulders embedded in the ice as it flowed over the north slopes of rocky hills and the plucking (or quarrying) of rocks from the south sides of the hills.
The Long Island region is made up of gravel, mud, sand, and boulders eroded from New York, New Jersey, and New England and carried there during the Wisconsinan Stage. Two moraines, Harbor Hill along northern Long Island and Ronkonkoma as the southerly moraine, with their associated outwash plains form the exposed part of the island; these two moraines merge in the western Long Island near the eastern end of Queens. South of the Ronkonkoma moraine is the outwash plain left after the retreat of the last glacier. One part of the outwash plain was known as the Hempstead Plains which contained one of the few natural prairies to exist east of the Appalachian Mountains (DeWan, George. "Long Island History: The Prairie That Was".)
Places to see the rocks
Fordham Gneiss and Yonkers Gneiss: Van Cortlandt Park, the Bronx.
Manhattan Schists: Central Park and Inwood Hill Park both in the Manhattan Island; a good exposure of the Hartland Formation is in Pelham Bay Park, the Bronx.
Inwood Marble: Isham Park, Manhattan Island.
Serpentinite: Route 278, Staten Island.
Palisades Sill: Graniteville quarry, Travis Avenue, Staten Island.
Anthophyllite. I-287 and Grymes Hill, Staten Island.
Clay. Clay Pit Ponds Park Preserve, Staten Island.
Pleistocene glacier deposits: Caumsett State Park, Long Island; Prospect Park, Highland Park, Brooklyn; Forest Park, Queens.
One hundred and twenty nine (129) valid mineral species have been found in New York City. Almandine, chrysoberyl, artinite, uvite, schorl, xenotime-(Y), titanite, goethite, zeolites, microcline, monazite-(Ce), muscovite, pyrite, dumortierite, and quartz are among the most interesting mineral species found during the excavations of the subway system, water tunnels, building foundations, city sewers, and so on.
Two museums in New York City have local specimens of rocks and minerals on display: the American Museum of Natural History (AMNH) and the Staten Island Museum. While the AMNH has only a few New York City minerals exhibited, the Staten Island Museum has a whole collection of local mineral specimens on display.
The New York State Museum in Albany has a New York City mineral display featuring its own specimens and minerals on loan from the New York City Mineral Club.
The early colonists of New York City searched for mineral resources as a way to make money to survive in the New World. There were many mining prospects located all over the city but only a few of them were profitable for even a short time. Iron, asbestos, diabase, and clay in Staten Island, and marble and gneiss in Manhattan were the main mineral resources that were mined.
The first evidence of iron mining occurred on Todt Hill (the Dutch name was Yserberg - Iron Mountain) in Staten Island in 1644, but intensive mining activity took place there only between 1832 and 1881. The ore formed as a weathering product on serpentinite and contained goethite and hematite. After an 1865 boom, the mining activity declined and ended probably in 1881 (http://www.nycgovparks.org).
Building and paving stones: The Inwood marble was mined from the Kingsbridge area in northern Manhattan for quicklime and building stones, but due to its poor quality the mining activity was abandoned in 1850. Gneisses for building stones were mined in Manhattan and Queens and diabase from the Palisades Sill was excavated at Graniteville and Travis in Staten Island for paving stones.
Asbestos: Fibrous anthophyllite from the Staten Island serpentinite was mined for asbestos insulation.
Clay: Clay was mined from clay pits in southern Staten Island for kaolin, bricks, terra cotta, and tiles from the mid-1800s until 1929. Amber, lignite, and fossil plant impression were preserved in clay.
Glacial Landforms in Central Park:
Field Guide: Geology of Central Park - From Rocks to Ice
Aleinikoff, J. N. (1985) – Isotopic and morphologic evidence for the age of the Fordham Gneiss. American Journal of Science, 285, p. 459-479.
Baskerville, c. A. (1992) – Bedrock and engineering geologic maps of Bronx County and parts of New York and Queens Counties, New York. U.S. Geological Survey Miscellaneous Investigations Series Map (scale 1:24,000).
DeWan, George. "Long Island History: The Prairie That Was". Newsday.com. http://classic-web.archive.org/web/20080415230214/http://www.newsday.com/community/guide/lihistory/ny-history-hs105a,0,5519292.story. Retrieved 2009-01-04.
D. W. Fisher; Y. W. Isachsen, L. V. Rickard, 1970, Geologic Map of New York State, consisting of 5 sheets: Niagara, Finger Lakes, Hudson-Mohawk, Adirondack, and Lower Hudson, New York State Museum and Science Service, Map and Chart Series No. 15, scale 1:250000.
Betts, J. H. (2009) - The minerals of New York City. Rocks & Minerals, 84, p. 204-240.
Okulewicz, S. C. (1990) – The new field guide to Staten Island’s rocks and minerals. Staten Island Institute of Arts and Sciences.
Merguerian, C. (1983) – Tectonic significance of Cameron’s Line in the vicinity of the Hodges Complex-An imbricate thrust model for western Connecticut. American Journal of Science, 283, p. 341-368.
Merguerian, C. and Merguerian. M. (2004) – Geology of Central Park-From rocks to ice. In: Eleventh Conference on Geology of Long Island and Metropolitan New York.
Merguerian, C. (1994)) – Section of geological sciences 1994 field trip – State Island and vicinity, New York. New York Academy of Sciences.
Schuberth, C. J. (1968) – The geology of New York City and environs. The Natural History Press, New York.