Meander maps of the Mississippi, made in 1944 by cartographer Harold N. Fisk, show the remarkable historical changes over the years in the flow of the lower Mississippi River. What Twain says of the changes in the morphology of the river over the course of days, hours, even minutes, add up to significant changes over time.
We could consider Twain’s comments on the changing river as comments on historical change on a number of scales, history of the nation, history of the region, even history of the individual.