A Geologic Barrier

A Geologic Barrier. . Canal engineers encountered many problems, but perhaps the most perplexing was navigating around the Great Falls of the Potomac., At Widewater the canal builders used a river channel abandoned thousands of years ago by the Potomac when it cut its present gorge. At this bend, just above Widewater, the engineers found a steep cliff where the old channel ended, and had to build an immense buttressed wall to cradle the canal and towpath about 70 feet above the present river level., Before the Ice Age the Potomac flowed at this level where the canal is now and had not yet cut the deep gorge you see below., As the sea level dropped during the Ice Age, the river cut its channel deeper to reach the lowered sea level., By about 10,000 B.C. the river had abandoned its old channel at Widewater and cut the new one you see today. Just upstream are the Falls, where sand and gravel carried by the river continue to scour and grind away the ancient bedrock.