New York Rocks

Interesting piece in the NYT Monday (I just got around to reading it) on the bedrock exposed as they're clearing the ground at the World Trade Center site. There are a number of ice age features including a pothole and scoured, polished rock from glacial runoff. The bedrock itself, from what I know and can infer from the article, is similar to the exposures in Central Park: high-grade metamorphics of early Paleozoic age. There are two pictures, and you can easily picture the water cascading over this surface. The first appears to show a horseshoe-shaped cut where the meltwater eroded back into a cliff face. In the second, closer image, you can also see what appears to be a basaltic/diabasic dike running across the face. The writer points out that the excavated surface is 70 feet below sea level, and the pothole another 40 feet deeper. He doesn't mention that sea level during peak glaciation was about 100 meters (~330 feet) lower than at present because so much water was stored on land as ice.