Complex sentence: Geologically, the Alpstein, different from the predominantly granitic central Alps, are a limestone massif and thus represent a kind of western continuation of the eastern ranges, running between Germany and Austria.
Split into simpler sentences: Geologically, the Alpstein massif, is different from the predominantly granitic central Alps. Alpstein are predominantly limestone massif and thus represents a kind of western continuation of the eastern ranges, running between Germany and Austria.