Alpine Club classification of the Eastern Alps (AVE) widely used by Austrian and German mountaineers, these mountain chains comprise several dozen smaller mountain groups, each assigned to four larger regions: Northern Limestone Alps Central Eastern Alps Southern Limestone Alps Western Limestone Alps For the breakdown of these regions into mountain groups see the List of mountain groups in the Alpine Club classification of the Eastern Alps. The Swiss Alpine Club (SAC) has a slightly different classification of the ranges, based on the political borders in the canton of Graubünden. In Italy the 1926 Partizione delle Alpi concept is quite common, recently superseded by the SOIUSA attempt to combine the different approaches. Other specific, especially hydrographical arrangements are also in use. Tectonics The Alps comprise four main nappe systems: The Helvetic nappes (Helveticum, ), with their main ranges in the Western Alps. They consist primarily of Cretaceous and Paleogene sedimentary rocks in multiple folds. The Penninic nappes (Penninicum), Jurassic sediments of the Tethys Ocean stretching from the Eurasian to the Apulian Plate, pushed together during the Alpine orogeny. They comprise a Flysch zone and several crystalline rocks in geological windows, such as the Engadin window and the Hohe Tauern window in the Central Alps. The East Alpine system: the Northern Limestone Alps, made up of Mesozoic (Triassic) rocks, the Paleozoic slate (Kitzbühel and Salzburg Slate Alps) and the greywacke zone, as well as the crystalline Central Eastern Alps, the Precambrian and Paleozoic remnants of a main strike. The South Alpine system (Dinaric nappes) south of the Periadriatic Seam (Valtellina—Tonale Pass—Puster Valley—Gailtal—Karawanks). They mainly consist of Mesozoic and Paleozoic formations (Carnic Alps, Karawanks and several smaller strikes) with little faults, whose nappes and folds are oriented towards the south. History The ice age During the Würm glaciation, the Eastern Alps were drier than the Western Alps, with the contiguous ice shield ending in the region of the Niedere Tauern in Austria. This allowed many species to survive the ice age in the Eastern Alps where they could not survive elsewhere. For that reason, many species of plants are endemic to the Eastern Alps. Ancient history The first signs of humans living in the area of present-day Liechtenstein can be dated back to the Middle Paleolithic era. Neolithic farming settlements appeared in the valleys around 5300 BCE. A Bronze Age settlement at the site goes back as far as the Pfyn culture (3900–3500BCE),