Bronx Zoo Erratics & Striations

Giant boulders (remember that “boulder” is a size) can be found throughout the Bronx and New York City. These boulders are called erratics.

Erratics do not look like the rock that you’d find if you dug down into the ground (this kind of rock is called “bedrock”). Some erratic are so big that they cannot easily be moved, even with a truck. In the past, you either had to work around them, or blow them up if you wanted to build a road or houses.

ð What are these boulders? Where did they come from?

Another mystery is the presence of long scratch marks or “grooves” in sections where bedrock is exposed. These are called striations. Striations are cut into the solid rock in the same direction in many areas in the New York City area and can also be found hundreds of mile North. All of them are parallel (they line up in the same direction).

ð What are these strange grooves? Why do they all point in the same direction?

One place where you can find many such erratics and striations is the Bronx Zoo.

At the Zoo, a look at the grizzly bear area reveals a particularly large area of exposed rock with striations cut into the rock and many erratics as well.

Just outside of the now-closed World of Darkness exhibit building is a large erratic called the Rocking Stone. The Rocking Stone was once balanced so finely that the force of one or two men could make it wobble. It rocked, but it didnt move.Fearing that one day someone was going to rock the Rocking Stone a bit too far, Zoo officials shored up its base in 1959