Tertiary Quartzite and Wellenkalk (Lower Muschelkalk): Dornburg Rocks @museum.de

It took 20 horses to haul this fifteen-ton boulder from the site north of here where it was found, to the town, which stands on higher ground. It was set up here in the market square in the early 1920s, and a bronze plaque commemorating the dead of the First World War was added.

This colossal erratic boulder was formed in a sandy river landscape during the Tertiary period, some 40 million years ago. Back then, the coast of the primeval North Sea was roughly at the level of Leipzig. To the south and west, there was a vast blanket of sand. Over millions of years, those sandy areas solidified. When minerals such as quartz fill the pore spaces between individual grains of sand, the result is a very solid sandstone called quartzite – or more precisely, tertiary quartzite.

The glaciers of the Elster Ice Age some 400,000 years ago eventually moved the heavy boulder several kilometres further south to where it was found.

Significantly more porous and more susceptible to weathering than tertiary quartzite is the shell-bearing limestone known as Lower Muschelkalk. It’s sometimes called Wellenkalk due to the wavy pattern – Wellen is German for waves – and makes up large parts of Dornburg Rock. This sedimentary rock was formed about 246 million years ago, when limy mud solidified. The burrowing traces left in the mud by shellfish and worms millions of years ago produced its wavy and gnarly shape. They’re also responsible for its tendency to crumble. Added to this are fractures, cracks and crevices formed during later geological eras, which significantly affect the rock's stability.

Fortunately, the Dornburg Wellenkalk slopes slightly to the west, that is, away from the valley into the hillside. But still – several times over the past decades, safety measures have been required to increase the stability of the rock and safeguard the town. Five-metre-high steel safety nets were installed just a few years ago to protect the road and secure access to Dornburg for decades to come.