The Champlain Sea in the Lake Ontario Basin

Abstract

The retreating front of the Labradorian ice sheet late in the Wisconsin glacial stage rested for a time against the northwestern slopes of the Adirondack Mountains. Between the ice front in the upper St. Lawrence Valley and the southern rim of the Ontario basin in New York state, the waters of Lake Iroquois were ponded. The history of this lake, with its outlet down the Mohawk Valley past Rome, New York, has been deciphered by Fairchild, Taylor, Spencer, Coleman, and others. Further withdrawal of the ice margin permitted the escape of the Iroquois waters through Gulf, southwest of the summit of Covey Hill, the northernmost hill on the west flanks of the Adirondacks, a mile north of the international boundary. The altitude of the Covey outlet at the present time is about i,ooo feet, while that of the Rome outlet is 460 feet, but, according to Fairchild,' the altitudes of the two outlets during Iroquois time were very similar, if not practically identical (see Fig. i). North from Covey Hill the land drops rapidly away to the broad, low valley of the St. Lawrence. As soon, therefore, as the edge of the ice sheet had withdrawn a mile or two farther northward, Lake Iroquois was drained. The water in the Ontario basin and the St. Lawrence Valley rapidly fell to sea-level, for the land stood at a much lower altitude then than now. Differential uplift of the Great Lakes region had commenced long before the extinction of Lake Iroquois, and it is commonly held that the Champlain Sea was then at its maximum extent. It has been more or less unconsciously assumed that the history of these sea-level waters in the upper St. Lawrence Valley was simply a slow but progressive