Group by age

Upper North Sea Group - NUMiddle North Sea Group - NMLower North Sea Group - NLChalk Group - CKRijnland Group - KNScruff Group - SGNiedersachsen Group - SKSchieland Group - SLSchieland Group - SLAltena Group - ATUpper germanic Trias Group - RNLower germanic Trias Group - RBZechstein Group - ZEUpper Rotliegend Group - ROLower Rotliegend Group - RVLimburg Group - DCFarne Group - CFCarboniferous Limestone Group - CLOld Red Group - ORBanjaard Group - OBSilurian - OS