Like the rest of the Rhenish Massif, this area is formed by folded and metamorphized rocks, the remains of the almost completely eroded variszian orogeny. Devonian Sediments are covered partly by igneous rocks, especially basaltic rocks and tufa. Typical natural resources are slate, limestone, clay and iron ore.
The limestone deposits are located in the eastern, Hessian part of the Westerwald. They are fossilized Devonian reefs, surrounded by non carbonatic deep water sediments. Namely, there is limestone near Breitscheid and near Homburg.