Only in the extreme northeast of Franconia and in the Spessart are there Variscan outcrops of the crystalline basement, which were uplifted from below the surface when the Alps exerted a northwards-oriented pressure. 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). The Fichtel mountains are also characterized by large granite bodies, called post-kinematic plutons which, in the late phase of Variscan orogeny, intruded into the metamorphic rocks. In most cases these are S-type granites whose melting was caused by heated-up sedimentary rocks sunk deep into the Earth's crust. While the Fichtel and Franconian Forest can be assigned to the Saxo-Thuringian Zone of Central European Variscan orogeny, the Spessart belongs to the Central German Crystalline Zone. The Münchberg mass is variously attributed to the Saxo-Thuringian or Moldanubian Zones.