The major rocks of the Kitzbühel Alps divide into two groups by age, the older rocks probably dating to the Ordovician period. For example, the deep underground complex of Wildschönau slate is quite uniform and has no fossils at all, just volcanic deposits. Above it lies weakly metamorphosed volcanic rock, up to 600 metres thick, made up of quartz porphyroids and tuff, mainly in the west (Hohe Salve, Hahnenkamm and Wildseeloder).