Swabian Jura  The Swabian Jura (, more rarely: ), sometimes also named Swabian Alps in English, is a mountain range in Baden-Württemberg, Germany, extending from southwest to northeast and in width. It is named after the region of Swabia. The Swabian Jura occupies the region bounded by the Danube in the southeast and the upper Neckar in the northwest. In the southwest it rises to the higher mountains of the Black Forest. The highest mountain of the region is the Lemberg (). The area's profile resembles a high plateau, which slowly falls away to the southeast. The northwestern edge is a steep escarpment (called the Albtrauf or Albanstieg, rising up , covered with forests), while the top is flat or gently rolling. In economic and cultural terms, the Swabian Jura includes regions just around the mountain range. It is a popular recreation area. The geology of the Swabian Jura is mostly limestone, which formed the seabed during the Jurassic period. The sea receded 50 million years ago. Three layers of different limestones are stacked over each other to form the range: Black Jurassic, Brown Jurassic, and White Jurassic. White Jurassic may be as pure as 99% calcium carbonate. Since limestone is soluble in water, rain seeps through cracks everywhere and forms subterranean rivers which flow through a large system of caves until they emerge. Thus there are hardly any rivers, lakes or other forms of surface water on the plateau. In some places, former volcanic activity has left traces, such as maars and hills. In the west, the Zollerngraben (a geological depression in a tectonically active region) sometimes causes mild earthquakes. The Nördlinger Ries is a large meteorite crater (15 million years old). Tertiary relicts can be found at the southern part of Swabian Jura. Famous locations are known in the Ulm area (e.g., Turritellenplatte of Ermingen). Constant rain and other weather influences are slowly dissolving the entire range. Each year, it recedes approximately . Some millions of years ago, the mountains reached as far as Stuttgart. In some places, the limestone was more resistant to decay and thus the recession of the main range has left small mountains (called "Zeugenberge"—"witness mountains" or outliers; e.g. the "Achalm" or the "Hohenstaufen") which testify to the former territory of the range.