Fig. 365.—Outline map of the Nipissing Great Lakes with their outlet past North Bay into the Champlain Sea.
The Nipissing Great Lakes.—We have now followed the ice front step by step in its retreat across the valley of the St. Lawrence system. The successive unblocking of outlets offers but one further possibility—the opening of the French River-Nipissing Lake-Ottawa River, or “North Bay outlet.” Though not so to-day, the bed of this ancient channel was then much lower than that of the “Mohawk outlet”, and so soon as the glacier had in its retreat uncovered this northern channel, the waters of the upper lakes discharged through it past the site of Ottawa and into an arm of the sea which then occupied the lower St. Lawrence valley and has been called the Champlain Gulf or Sea ([Fig. 365]). The level of the waters was lowered and the area of the lakes correspondingly reduced.
The reader who has had no opportunity to observe these ancient channels which carried the swollen waters of the former glacier lakes, will find it interesting to consider that every one of them has been fixed upon by engineers for improvement as artificial waterways. Thus we have the Illinois Drainage Canal and projected ship canal along the “Chicago outlet”, the projected Mississippi-Lake Erie Canal along the “Fort Wayne outlet”, the Grand River canal project to connect Lake Michigan and Saginaw Bay along the course of the “Grand River outlet”, the Trent Canal along the “Trent outlet”, the Erie Canal along the “Mohawk outlet”, and, lastly, the proposed Georgian Bay ship canal to the ocean along the “North Bay” or “Nipissing outlet.”
Summary of lake stages.—We have omitted in this summary of late lake history in the Laurentian basin all the less important lake stages, including some of a transitional nature which were represented by beaches and outlets easily traced to-day. This is because it is an outline only which it seems best to present, and the episodes of this abridged history may be tabulated as follows:
EPISODES OF GLACIAL LAKE HISTORY
Mississippi Drainage
Lake Maumee (early), Fort Wayne outlet.
Lake Maumee (late), Imlay City outlet.
Lake Arkona, “thumb” outlet.
Lake Whittlesey (with readvance of glacier), Ubly outlet.