Jungfrau-Aletsch-Bietschhorn (JAB) is the most glaciated part of the Alps, containing Europe's largest glacier. The JAB region provides an outstanding example of the formation of the High Alps which resulted from uplift and compression during the Tertiary geological period 20-40 million years ago. Within an altitude range from 900Mto 4,274M, the region displays 400 million year old crystalline rocks thrust over the younger autochthonous (rocks formed in situ) calcareous sediments due to the northward drift of the African tectonic plate.