The World Trade Center excavations this summer revealed traces of glacier carvings that presumably formed 20,000 years ago, engineers at Mueser Rutledge Consulting Engineers reported. Taking a step back in time, the Lower Manhattan site now tells the story of processes that occurred thousands of years ago, mixing together different formations in what appears to be a huge pothole.

The discovery came as a surprise, and as Cheryl J. Moss, senior geologist at Mueser Rutledge told The New York Times, although there are other areas in local parks where vertical potholes have been exposed, she did not expect to find a 40-foot depression in the city.

The discovery is intriguing and exciting for geologists, as they are now looking at an area with a wide variety of glacial deposits from the Palisades, the Ramapo Mountains and the Newark Basin, which is unique not only for the city, but also from a geological point of view, since it is very unusual to find such features near sea level, as Charles Merguerian, chairman of the geology department, Hofstra University said.

As he explained, the layers of rock exposed here talk of events that took place 500 million years ago, when the edges of the colliding North American and African continental plates gave the vertical orientation to the rock layers visible on the east side of the pothole.

Unfortunately, this is not a site to study much, since it will all soon be covered, as this ultimately remains a site under construction. “It’s nice to look at,” Robert B. Reina, supervising structural engineer at Mueser Rutledge told the same newspaper, “but it’s all got to go.”