HISTORY OF THE CHAMPLAIN SEA
As mentioned earlier, the Champlain Sea resided in what is referred to as the Ottawa-St. Lawrence Lowland. This area, which today contains the Great Lakes, was and is bounded by highlands that marked the borders of this epicontinental sea. Marine waters from the Atlantic Ocean entered the sea from the east, and flowed southwest until impeded by the Frontenac Arch, a low arch of Precambrian rock that bridges the Madawaska Highlands and the Adirondacks. These limiting regions are shown in the map below (modified after Harington).