 These are rocks of pre-Permian vintage, which were folded during various stages of Variscan orogeny in the Late Palaeozoic - before about 380 to 300 million years ago - and, in places, were metamorphosed under high pressure and temperature or were crystallized by ascending magma in the Earth's crust.Rocks which were unchanged or only lightly metamorphosed, because they had been deformed at shallow crustal depths, include the Lower Carboniferous shale and greywacke of Franconian Forest.The Fichtel mountains, the Münchberg Plateau and the Spessart, by contrast, have more metamorphic rocks (phyllite, schist, amphibolite, gneiss).