More than 300,000 years ago the Mississippi did flow through the eastern edge of Forest Park during the Illinoian glacial period. The Museum of Science and Natural History has placed a plaque to mark the location of the ancient riverbed and explain how the mighty river was dislodged from its customary path by a lobe of glacial ice. Some of the meltwater from the ice flowed along the western edge of the glacier in a channel that is now the Mississippi River.
Glacial ice is far from clean.
It contains fragments of rock debris of all sizes - boulders, pebbles, sand and clay. When the ice melts, a distinctive type of sediment accumulates on the ground. It is an unsorted jumble of rock fragments of all sizes which is called till. The distribution of till in St. Louis leads us to believe that the glacier advanced no farther west than Kingshighway. Due to vagaries in ice motion, glaciers tend to flow in lobate patterns.