Geologically, the Thuringian Forest is defined by a belt of strongly uplifted and deformed metamorphic and igneous rock that divides the relatively flat sedimentary plains of the "Thüringer Becken" (to the northeast) from similar rock formations in the valley of the Werra (to the southwest). It consists of a large fault block in hercynian orientation, which consists from sandstones and conglomerates of Rotliegend age in its western parts (Eisenach trough), followed by granites and gneisses of the "Ruhlaer Kristallin" formation of early paleozoic origin which were uplifted in the Rotliegend era, and the conglomerates, sandstones, and abundant volcanic rocks (rhyolites and andesites) of the Oberhof trough. Ore deposits associated with the upthrust of the range have been of significant historical importance in the development of the region, for example, the metalworking tradition in Suhl and the mining history of Ilmenau.