F: You’ve probably noticed the diagonal line on the floor. There’s something in there, under a sheet of glass. Have you taken a closer look? That’s a drill core from Hennef-Rott, recovered in 1989. It shows the various strata – from volcanic tuff at a depth of 34 metres, via the oil shale deposits (with the fossils) at a depth of between 32 and 31 metres, to the younger layer of pale clay at a depth of 12 to 11 metres – equivalent to depths of 111, 103 and 38 feet respectively. That last deposit was crucial for the development of ceramics production in Siegburg.
M: At the far end of the room, there’s a historical recreation of Siegburg’s city wall from the mid-19th century. Like many other stone structures in Siegburg, the wall was built from what’s known as "Wolsdorfer Brocken" – a basalt tuff of volcanic origin. It was quarried in a range of hills called the "Wolsberge" in the Siegburg suburb of Wolsdorf. Feel free to touch the wall. What do the stones feel like?
F: Quite soft, aren’t they? Volcanic stone is very lightweight and fluffy, because it’s extremely porous. It was used as construction material in Siegburg for centuries and still shapes the city’s appearance today.
M: In the centre of the room, there’s a geological model of the Siegburg-Bonn area, which shows how the present landscape developed.
F: Here’s the story – with some big gaps in the timeline:
M: About 400 million years ago, the entire area was covered by a vast primeval ocean. In the Tertiary period, roughly between 30 and 25 million years ago, volcanic activity began – and decisively changed the landscape. This was the period when the tops of the legendary Seven Mountains, the Siebengebirge, were created. It also saw the formation of the Michaelsberg and the Wolsberge in Siegburg.
F: The model shows which structures in Siegburg and the surrounding area were formed during which geological eras.
M: Before you move on, do take a moment to look at the selection of rocks and minerals from our geological collection in the showcases.
Fotos: © Dagmar Trüpschuch