The cliffs are pre-Cambrian rock that was once the ocean floor of a tropical sea, and the layers are different sediment accumulations on that open floor. Then the oceans dried up and the glaciers came, carving the rock into these 200 foot cliffs and leaving behind Lake Superior.
Lake Superior is the largest freshwater lake in the world by volume and contains more water than all the other Great Lakes. If you emptied the other four Great Lakes into it, you would need three more Lake Eries to fill it up. It is 400 miles long, 160 miles wide, 1400 feet deep. And chilly. 40 degrees on average. Did I mention blue and clear?