New York City Geology and Architecture Transit System

Manhattan Geology

Much of Manhattan lies on the Manhattan schist formation, made up of "Paleozoic and Proterozoic metamorphic and metamorphosed igneous rocks crystalline basement rocks" (Merguerian) that form a solid bedrock base for the soaring skyscrapers of Manhattan. Without this rock-solid base, much of the building in Manhattan would not be possible. Of course, this solid rock core of the island also helped create difficulties in excavating and in construction. These igneous rocks "are subdivided into two basic sub-layers, an older sequence consisting of ~1.0 Ga (billion year old) gneisses (Layer I) and a younger sequence of complexly deformed and internally sheared schist, gneiss, amphibolite, and marble (Layer II)." Some of this bedrock is exposed throughout Manhattan, while much of it is buried deep under a layer of .... This deep bedrock is strong and enduring, aid it also "forms the spine of the island and provides the foundation for its tall buildings outcrops in Central Park." While the Manhattan schist proved to be a boon for building support, it was also used to construct some famous buildings throughout the city. Harris Hall, once the Main Building on the campus of City College, located on Amsterdam Avenue is constructed of Manhattan schist that was quarried from a nearby subway construction site. The schist has darkened with age, provided a startling contrast to the white terra cotta trim on the distinctive building.

Thus, the strata underneath Manhattan helps support the infrastructure above, and also creates building materials that can be useful throughout the island. This bedrock is also a natural support system to the city's conglomeration of subway and highway tunnels that run throughout the city. It forms a solid base once excavation is completed.

There are also several fault lines in New York and in New York City. What was once considered to be a single layer of Manhattan schist is now understood to be "three ductile fault bounded sheets of rock that are intricately folded together," and these layers shifting against one another is a contribution to causing earthquakes in the area. The most recent event was an earthquake centered along the 125th Street "Manhattanville" fault that occurred in January 2001. The 2.4 magnitude quake was mild, but indicates that the bedrock is not nearly as stable as early builders may have believed, and that much of the city's grid follows the natural fault lines of the area. In fact, the Lincoln Tunnel crosses a major fault line in the area, too, which indicates that much of the city was laid out before the fault lines were established and understood.