Glacial erratic boulder. Thatcher Woods, River Forest, Illinois.2012-14746While running errands a few days ago, I took a short walk in Thatcher Woods, just south of North Avenue. On the way back to my car, I noticed something I’d never seen there before, a huge glacial erratic boulder. It’s just off the newly paved area at the pumping station between Greenfield and North Avenue. I’m not sure whether it was visible due to recent brush clearing or it was dug up during the construction project that included the paving.