“The best part of this job is getting to see parts of the Earth no one has ever seen before,” said Scott Chestman, chief geologist for the Second Avenue subway construction. He spoke rapidly and lovingly of the stone that forms the foundation of his native New York City.

The rock under Manhattan is unique. Called Manhattan schist, it was forged some 470 million years ago during the formation of the supercontinent Pangaea.

Unlike the rock beneath nearby Queens and Brooklyn, which is much harder to bore through, the rock in Manhattan is soft and easy to excavate. “It cuts like butter,” Chestman said.

Drill Down: Going Deep With NYC’s Second Avenue Subway Project | Wired Science | Wired.com