When passing through the Narrows it is easy to imagine how this landscape was formed over millions of years. The mountains rise from all corners creating the feeling of being in a flooded lowland, while tiny islands –the remains of mountaintops scraped away by glacial movement – dot the waterway.
Before the last Ice Age began, the lakebed consisted of two separate valleys whose rivers flowed in opposite directions. One stream rose to the west of Tongue Mountain and flowed southeast, around the east flank of French Mountain. The other drained north, skirting the west side of Rogers Rock to reach the Trout Brook valley in Ticonderoga
Beginning about 1.5 million years ago, a continental ice sheet crept down from the north, eventually building up to a mile thick. It gouged out valleys and scraped over mountains, leaving only the hardest rock behind. When the climate warmed and the glacier began to melt, all the soil and rock in the ice fell to the ground. Tons of materials dropped right into the river courses,, effectively damming them up. Water filled the new lake until it found an outlet over the natural dam at the north end of the valley.