The Alpine orogeny occurred in ongoing cycles through to the Paleogene causing differences in nappe structures, with a late-stage orogeny causing the development of the Jura Mountains. A series of tectonic events in the Triassic, Jurassic and Cretaceous periods caused different paleogeographic regions. The Alps are subdivided by different lithology (rock composition) and nappe structure according to the orogenic events that affected them. The geological subdivision differentiates the Western, Eastern Alps and Southern Alps: the Helveticum in the north, the Penninicum and Austroalpine system in the center and, south of the Periadriatic Seam, the Southern Alpine system.