Köln

Cologne


The city Köln (Cologne) on the Rhine, in the Kölner Bucht (Cologne Bay or Cologne Lowland), between the Eifel, Sauerland and Westerwald. In geographical terms, it is the southernmost tip of the North German Plain. The area was lowered 30 Ma ago and then filled with gravel by the Rhine. In other words, the subsoil consists of fairly young river sediments that are not suitable for cave formation. However, there are a large number of artificial underground sights in the city of Cologne, as is common in large cities.

The area is famous for its open cast mining for lignite, which has been an important source of energy until lately. Due to the subtropical climate 15 Ma ago, there was a abundant plant growth in the basin. The swampy vegetation formed thick layers of peat, up to 270 m thick. More sediments which were deposited on top created pressure and compressed the peat which was transformed into lignite.