Mesozoic and Paleozoic upper crust with emphasis on the petrothermal Lochkovian reservoir (in blue). Cross section modified from Schintgen et al. (2015). For location of the cross section, see Figure 1. L/D and dash-dotted line mark the German-Luxembourgish border. Vertical exaggeration is twofold. Red faults represent faulting in the Eifel Depression. Black vertical columns (width not to scale) indicate schematic feeder dikes of Eifel volcanoes.