Lessons In Geology
Rivers expose the geology as they cut down through the rocks to make valleys (or as they are pushed up by plate tectonics) and they are an active force of geomorphology as they shape the land around them. One of the pleasures of canoeing is to see this and appreciate this at close quarters.
After some time spent on the river you will soon become acquainted with the way a river works; the way the river actively cuts the shore on the outside of bends and slows on the insides of bends to deposit silt. If you are looking you can see how a river snakes its way down a valley as the meanders move like a rope being flicked at an immensely slow pace. Ox-bow lakes are evidence of this and those places where you might think to cut across an isthmus to shorten a paddle around a long bend.
When canoeing in deep gorges or in valleys bound by cliffs you can also see the exposed rocks. The history of time is laid out before you and if you are canoeing, for example, on the Vezere in France you can be suddenly aware that people like you were paddling this way 40,000 years ago and these cliffs would have looked much the same.