The work reported has a background in several principles of fluvial hydraulics: the tendency to flow in channels, the concentration of fluvial force against concave banks, the mechanism of interdependence, the importance of approximate grade and its result, non-vertical corrasion. An example of breaching by lateral corrasion of a bedrock meander neck is described, and evidence from maps is brought forward to demonstrate horizontal bedrock erosion at a rate of 1 foot a year. A rate of upstream knickpoint migration of 100 feet a year is established from observation. A topographic form consisting of a slip-off slope with a prominence at its lower end is given the name "pembina"-the origin of which is traced to non-vertical corrasion. The theoretical search for this origin is dependent on the hypothesis of unequal activity.
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C. H. Crickmay (1960) studied this question.