The notion of cycle in geomorphology: After giving an analysis of Davis' fixist point of view, and of Penck's mobilist one, the author adopts the balanced appraisal expressed by J. Leighly, some fifty years ago: "I think that a thorough examination of the two systems will lead to the discovery of useful ideas in both, and in both ideas that should be rejected... The ideal, complete theory of the future will include part of Penck and part of Davis, but not all of either". Examples taken from Western and Central Europe show that erosion surfaces belonging to sedimentary basins and the periphery of surrounding old lands are indeed acyclic planation surfaces. They also show that, genetically speaking, such planation surfaces are much more closely linked with the Penck's Primärrumpfe (= primary peneplains) than with Davis' peneplains (Endrumpfe = end-peneplains). Inversely, from the Amorican to the Bohemian massif, the piedmont benchlands (= marginal benches) observed on the slopes or at the foot of many variscan massifs are evidence, in all likelihood, of pulsational uplifts (as Davis saw it), rather than of continuous crustal movements, gradually accelerated, according to Penck's views (waxing development). Far from being mutually exclusive, polycyclism and acyclism are two geomorphic evolutionary models which are not only compatible, but also complementary.
