Situated at the northern tip of the Erzgebirge, the gneiss of the Freiberg dome form the base of the Tharandt Forest, which has a cross-section of only 10 km. Its geological development reflects the entire geological history of Saxony. The classical storey structure, complete with bedrock, transition rocks and overburden, can be studied here at a short distance. Besides the gneisses of the Ore Mountains, rocks of the Nossen-Wilsdruff Slate Mountains (Ordovician to Devonian) form the bedrock. During the time of the “Rotliegend” there were strike-slip faults under elongation regime in the area of the Elbe zone. This led to the formation of the Doehlen Basin and its filling with the erosion debris of the Variscan Mountains.
The distinctive almost circular shape of the Tharandt Forest between Freiberg and Freital owes its shape to a magmatic eruption with subsequent caldera collapse in the Permo-Carboniferous. Acidic effusive rocks (rhyolites) were formed, which are classically divided into the quartz-poor porphyry (two thirds of the area) and the quartz porphyry.
After a pause of 220 million years, the earth's history once again presented us with a peculiarity that has been preserved thanks to the mild erosion in the area of the Tharandt Forest. On the rhyolite plate, remains of Cretaceous rocks have been preserved, which are part of the sedimentation in the Saxon Cretaceous Basin. Before the sea of the Cenomanian washed over the flanks of the Ore Mountains, a river coming from Bohemia drained here in the direction of today's Elbe valley. Large-scale movements in the earth’s crust during the Cenozoic manifested themselves in the Eger Graben with intensive volcanic activity. Among the most widely dispersed volcanic formations of this period are the basaltoid rocks of Ascherhübel, Landberg and Buchhübel in the Tharandt Forest. Today it is assumed that all three belong to a uniform effusive cover with an eruption centre at Ascherhübel. With an age of about 10 million years, the basalts, which are actually olivine-augite-nephelinites, are very young.
