Here, at the abandoned quarry at the Weilberg mountain , we see the structure of the rocks and get an idea of how the Siebengebirge came into being. About 30 million years ago, in the Oligocene and into the Miocene, there was volcanic activity in our region.
In a first phase of eruption, lava and large quantities of stones were ejected from the interior of the Earth to the surface where they slowly cooled off. These were the trachyte tuffs, and an area much larger than today’s Siebengebirge was covered by them. In a second phase of volcanic eruption, the trachytes came, yet they got stuck in the thick layer of trachyte tuffs, arched it upwards, forming numerous mountains: Drachenfels, Schallenberg, Geisberg, Jungfernhardt, Lohrberg, Perlenhardt, Wasserfall, Großer Ölberg und Lahrberg. In a third phase of volcanic eruptions, the latite tuffs and latites appeared. They broke through the layer of trachyte tuffs and on their turn formed mountains: Wolkenburg, Bolvershan, Hirschberg, Stenzelberg, Lahrberg, Himmerich, Mittelberg and Broderkonsberg. The last eruption phase occurred in the Miocene, now the lava brought basalt and basalt tuffs. The last mountains to appear were Asberg, Leyberg, Scheerkopf, Petersberg, Nonnenstromberg, the core of Großer Ölberg, Kleiner Ölberg, Dollendorfer Hardt, Rabenley Finkenberg. In millions of years, wind and weather gave the Siebengebirge its present form.
The early geologists, and even the world-renowned scientist Alexander von Humboldt, could not believe that the Siebengebirge was of volcanic origin. Today we know that our region, the Middle Rhine, was part of a continental fault line system. Along these lines continents may break apart, and volcanic eruptions may occur. In the Nature Park House at Margarethenhöhe, you can learn a lot more about rocks, volcanism in the Seven Mountains and petrology as well as in the Siebengebirgsmuseum.
The history of the Siebengebirge is also a history of the quarries. Large parts of the Cologne Cathedral were built with trachyte from the Drachenfels. The latite of the Wolkenburg was used for the facades of Baroque palaces, that of Stenzelberg for the construction of the Abbey Church of Heisterbach. Since the time of Napoleon, basalt was used to constructs roads and railroads, and finally the Prussians used it to build their fortifications.