A formerly active volcano, the Pechsteinkopf above Forst, distributed large amounts of volcanic rock in primeval times. There are therefore several balsalt veins underground, which fan out at the end of the valley. Loose basalt boulders on the surface as well as weathered red red sandstone soil and sandy loam. At a depth of about 2 m, as in many Forster sites, there are clay and limestone layers. The proportion of clay and loam in the pitchstone results in a high water capacity of the soil, from which a high level of mineralization and perfect water balance during the vegetation period can be derived. A great physiological maturity is the result. (Reichsrat von Buhl)