The red sandstone overburden with striking steps rises above the crystalline base (basement) in the northern Black Forest and in the adjacent parts of the Central Black Forest. The most resistant surface layer on the stepped surface of the Grindenhöhen, which is strongly dissolved by the Murg tributaries and the closed Enzhöhen, is the silicified main conglomerate (Middle Buntsandstein). To the east and north are the slabs of the Upper Buntsandstein (slab sandstone and red clay). South of the Kinzig, the red sandstone narrows to a border in the east of the mountains.
Ice Age and Shaping
It is considered proven that the Black Forest was heavily glaciated during the high phases of at least the Riss and Würme Ice Age (up to about 10.000 years ago). The glacial treasure trove characterizes almost the entire Black Forest and the main ridge of the Northern Black Forest. Otherwise it is only conspicuous in a large number of mostly northeast-facing Karen. Particularly in this exposition, snow accumulations on the slopes of the summit plateaus turned away from the sun and wind led to the formation of short karst glaciers, which carved out these funnel-shaped hollows. Some cirque lakes are still preserved in them, partly due to re-damming, such as Mummelsee, Wildsee, Schurmsee, Glaswaldsee etc.
Gneiss rocks predominate in the basement. Several large granite bodies penetrated in the course of older mountain formations. These can be found, for example, between the Kinzig and the Middle Murgtal. The formation of ore deposits was associated with igneous phenomena, some of which man used for mining. Also worth mentioning are the depressions in Rotliegend, for example the Baden-Baden depression, with partly thick quartz porphyry and tuff ceilings (exposed on the Battert rock massif, in the urban district of Baden Baden).
The Black Forest, which arose in the Young Tertiary - Paleocene - was, as it were, bulged to varying degrees like in a huge wave movement. The southern Black Forest with the Feldberg as the highest center (1493 m) was recorded most intensively, while the area around the Hornisgrinde (1164 m) was less powerful. In between lie broad, tectonic hollows like the river valleys of Kinzig and Murg. The Black Forest consists of two geological units: an older crystalline base, also known as the basement, and the overlying cap rock made of red sandstone.