The geological history
The St. Lawrence’s geological history dates back to the last ice age, 25,000 to 10,000 years before our time. Climatic warming gradually melted this ice, and the ice cap began to recede in southern Québec.
When the glaciers retreated, the land was covered by the Champlain Sea, which was created by the ice melting about 13,100 years ago. This temporary inland sea covered a vast expanse over the entire modern-day St. Lawrence valley, stretching to Saguenay-Lac-Saint-Jean to occupy part of the Ottawa valley and submerging present-day Lake Champlain. It disappeared about 10,600 years ago when the Canadian Shield was displaced upward.
Over millennia, and as the continent rose, the Champlain Sea gave way to the St. Lawrence River, the waterway that serves as the outlet for the Great Lakes. Today, the St. Lawrence runs in Logan Fault and a geological formation called the “St. Lawrence Platform”, a narrow, relatively flat strip bordered by the Canadian Shield to the north and the Appalachians to the south.
The first lighthouses