About 250 million years ago, when the important salt deposits of the Werra area and the southern Harz were formed in the Zechstein Sea, there was an island area in the Schmalkalden-Ruhla area into which the Zechstein Sea encroached like a fjord. In the geotope "Zechsteindiskordanz Auwallenburg", a former cliff of the Zechstein sea made of grey mica schist (garnet-staurolite-branch mica gneiss) can be seen. The upper edge of the cliff dips to the right and reaches the bottom of the railway cutting to the right of the bridge - in front of the right recess in the retaining wall. The sea, coming from the right, has deposited the whitish-yellow plate dolomite (limestone) of the Zechstein against the cliff and later also over it. The older deposits of the Zechstein are missing here, which is why it is called an unconformity.
Text & drawing: Dipl.-Geol. Volker Morgenroth, Schmalkalden