450 Million Years Ago, Hell’s Kitchen Earned Its Name

“That’s ancestral North America out there,” said Sidney Horenstein, the geologist and environmental educator emeritus of the American Museum of Natural History, gesturing broadly toward the towers of mid-Manhattan. “Here, we’re on this exotic continent that collided with it.”

Exotic is the word. The rock outcrop that emerges like the tip of a geological iceberg from the children’s playground in DeWitt Clinton Park, at West 52nd Street and 12th Avenue, is an astonishing work of natural sculpture; utterly sensuous — almost sensual in spots — with smooth curves and bubbly folds and veinous striations that look too organic to have been formed of schist, gneiss and amphibolite.

Still, that’s not what Mr. Horenstein means when he uses the word “exotic.” This outcrop near the Hudson River is what geologists call an exotic terrane, a fragment of the crust from one tectonic plate that has been sutured onto another and therefore differs in its composition from the surrounding rock. The only other visible example of this particular terrane in New York City, Mr. Horenstein said, is at Pelham Bay Park in the Bronx....