 Although Lake Algonquin did have two outlets (past Chicago and Port Huron), sufficient reason for its later complete discharge by Port Huron is found in the fact that the latter outlet was through easily eroded drift deposits and the Chicago outlet was over a rock sill.Numerous ridges in the southern portion of the Lake Michigan basin at levels a little below that of the Toleston beach probably belong, the higher to Lake Algonquin and the lower to Lake Nipissing.Most of them rise above Lake Michigan, or about above sea level, but some reach about and others not more than .