Object #9: Manhattan Schist

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Who knew so many of our listeners were geology enthusiasts? Or that, to use a pun Leonard would probably dream up, they really know their schist? Charles Merguerian, chairman of the Geology Department at Hofstra University, seemed surprised and then pleased that New York City bedrock made the top ten of our list. He said “People always ask: What came first the chicken or the egg? But the answer is rocks. Rocks are so fundamental and basic to us and our existence that there is a natural tendency towards wanting to know about them.” (continue reading)

Manhattan schist, which you can see outcroppings of around the city, started out about half a billion years ago as layers of sediment that tectonic forces slammed together, turned sideways, cooked at intense pressure and heat, and then ripped apart. “It’s gorgeous how it preserves the tectonic folding from the continental collisions,” Professor Dave Walker of Columbia University said of the unique shape of certain schist formations. “It’s a work of art on steroids.”

Millions of years later the region also went through periods of glaciations, when huge sheets of ice acted like incredibly coarse sandpaper driving groves into the rock. “The marks of that are quite visible in any bedrock in the New York area.” Prof. Walker told us. “You’ll see lots of furrows that run roughly North-Northwest to South-Southeast.” That’s roughly in the direction the glaciers descended upon us.

One of the main qualities that makes Manhattan schist so important to the city is its strength. Professor Merguerian said, “The bedrock in New York City is kind of like a huge chunk of Swiss Cheese with all these [man-made] tubes and tunnels. It’s the mechanics of the rock mass that enables that kind of deep level construction.” If you’re digging a subway or driving steel and concrete into the ground to support a skyscraper, it's important to have strong, durable rock at a vertical orientation to work with.

Manhattan has two distinct groupings of skyscrapers in downtown and midtown with a sort of building valley in the middle. For years, people have attributed the lack of tall buildings in that area to schist distributions. But that may be a myth. A recent study cited social and economic factors as the cause of New York’s unique skyscraper placement. In an interview with the Observer, Economics Professor Jason Barr argued: “It’s the wealthy and the middle class. If you’re an insurance salesman, do you really want to be traipsing through the slums of Five Points or the factories of Soho to get to work? That land was cheap, but the location was worthless.” What a difference a few decades of gentrification makes.

Though the political, economic, and social foundations of New York City always seem to be shifting, one thing is always certain: the place is built on very solid ground.