Illinois' Biggest Erratic?

Dick Berg (top) and Mike and Sara Waite with large glacial erratic in southern IllinoisIn southern Illinois, near Texico in Jefferson County, about 50 miles north of the southernmost extent of continental glaciation in the northern hemisphere, lies perhaps the largest erratic in Illinois. Erratics are exotic rocks brought to Illinois by the continental glaciers of the Great Ice Age as they scoured, scraped, and plucked pieces of bedrock during their southward advance. This erratic, composed of pink granite most likely originating from the Canadian Shield north of Lakes Huron and Superior is particularly interesting because of its size (about 22 feet × 10 feet × 11 feet), estimated weight (more than 100 tons), and its location. The erratic is about 75 miles south of the southern limit of the last glaciation (Wisconsinan) that occurred about 23,000 years ago. The rock was transported about 1,000 miles by the glaciers of the Illinoian or earlier glaciations about 150,000 years ago. Erratics of this size are very rare, particularly so far south.

The large erratic has grooves on one side, indicating some scouring on its journey or that these grooves may have occurred prior it being picked up by the ice. However, if the erratic had been at the bottom of the glacier for an extended time period, it would have been ground up. To remain intact for such a long journey, the erratic must have been on top of or within glacial ice. Further brief inspection of the region around the erratic revealed numerous smaller erratics (diameters of 1 to 4 feet). Some were exotics and others had lithologies of local shale. This concentration of erratics might be a smaller scaled version of the "boulder belt" near Ohio's glacial terminus. As the underlying ice, containing boulders, melted and the glacier receded northward, the boulders—like a conveyor belt—were brought to the surface of the ice and deposited.

The Texico erratic, known affectionately as "Elephant Rock" by landowners Mike and Sarah Waite, has been the venue for picture taking at family holidays and special occasions for about 60 years. Apparently the erratic recently "fell" from the side of the creek, rotated, and is now residing in the creek bottom. According to Sarah Waite, the dark band on the rock represents the original ground surface prior to the rock falling in towards the creek in recent years. When she first viewed the rock, only the upper, lichen-covered portion of the rock was exposed, and it looked like the back of an elephant.