Much later, the polar ice cap crept four times down across the continent, covering the region with ice to a depth of a mile or more. As the climate changed, the ice melted, the last great ice flow, the Wisconsin Glacier of the Pleistocene period, which covered much of the northern half of North America, retreated, and an outlet for the melting water developed through the Sag River and the Des Plaines River Valley around Mt. Forest, in the area known as the Palos.
The Kankakee Torrent poured through those valleys, eventually leaving behind the prehistoric Lake Chicago or Glacial Lake Chicago, the term used by geologists for a lake that preceded Lake Michigan when the Wisconsin Glacier retreated from the Chicago area, beginning about 14,000 years ago.
|This undated marker is located in the southern portion of Lincoln Park, on the foot path paralleling the east side of Stockton Drive. A second identical marker is located on the same ancient beach ridge 485 feet East-North-East from the first one.|
Compiled by Neil Gale, Ph.D.
 Moraines are accumulations of dirt and rocks that have fallen onto the glacier surface or have been pushed along by the glacier as it moves.