Next, reefs began to develop in the shallow waters of the sea, in which small coralline algae (haptophytes) and corals lived. Their dead, limy skeletons form the most important rock: Wetterstein limestone. This mostly bright white and weather-resistant limestone contrasts strongly with the other rocks. It forms the striking summits of the Mieminger and Wetterstein Mountains, not least the Sonnenspitze, Igelskopf and Zugspitze. Because Wetterstein limestone contains few plant nutrients, its scree and talus slopes are largely unvegetated and this tends to characterise the scene above the tree line.