 It was an elaboration of the uniformitarianism theory that had first been proposed by James Hutton (1726–1797).With regard to valley forms, for example, uniformitarianism posited a sequence in which a river runs through a flat terrain, gradually carving an increasingly deep valley, until the side valleys eventually erode, flattening the terrain again, though at a lower elevation.It was thought that tectonic uplift could then start the cycle over.