Farther south, near Chambers Street, it comes again to within about one hundred feet of the surface. Here, near New York University, the surface of the bedrock drops appreciably-up to several hundred feet below the street level. But when one reaches the north side of Washington Square in Greenwich Village, the situation changes rather abruptly. South of 30th Street…the mica schist, however, is still accessible in deep foundations or excavations. Originsīut how did the myth begin? It seems it was first written down by a well-known New York geologist, Christopher Schuberth, who, in his 1968 book, The Geology of New York and Its Environs, took some liberties by steering away from his expertise to write about urban land use:
The island’s two skyscraper districts were a result of Manhattan’s economic and demographic history. Why are skyscrapers “missing” from between Downtown and Midtown Manhattan? Contrary to what many believe, accessibility to the bedrock did NOT shape the skyline. It is appealing because, like all founding myths, it helps connect the dots between the great powers of heaven and earth and our humble lives. It perpetuates itself because it is constantly repeated by seemingly authoritative people- geologists and tour guides, in particular. It is true that skyscrapers more frequently appear where the bedrock is relatively close to the surface, but it is incorrect to conclude that access to bedrock was the reason. Let me be clear: this notion is false–a case of confusing correlation with causation. And, they avoided places in between where the rock was, presumably, too far down. The skyline tale says that developers naturally gravitated to those parts of the island-Downtown and Midtown-where bedrock was accessible. In parts of Central Park, the bedrock crops out above the ground, making for fun summertime climbing. Then at about 14 th Street the bedrock approaches the surface again, where it remains relatively close for the rest of the island. Going north, say along Broadway, it begins to dip, and by the time you get to City Hall, a mile (1.6 km) to the north, the rock floor gives way to a valley, far below the streets. Starting at the southern tip of Manhattan, it is relatively close to the surface. Manhattan Island-really just one big 13 mile (21 km) long boulder-would be ideally suited to support millions of humans and their structures.īut the bedrock is not flat. One possibility is to anchor them directly to the bedrock. Since skyscrapers are so tall and heavy, they require proper foundations to prevent them from leaning, sinking, or cracking.
In particular, the story says that Manhattan’s skyline is the way it is because of geology. It has to do with why skyscrapers are “missing” between Downtown and Midtown. There’s a popular historical anecdote about Manhattan that’s frequently bandied about at cocktail parties and on hop-on-hop-off bus tours.
#Floating foundation chicago skyscraper series#
Note: This two-part series is adapted from chapters seven and eight of my book, Building the Skyline: The Birth and Growth of Manhattan’s Skyscrapers (OUP, 2016), which is based on research ( here and here ) performed with Troy Tassier of Fordham University.
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