Group by age

Upper North Sea Group - NU Middle North Sea Group - NM Lower North Sea Group - NL Chalk Group - CK Rijnland Group - KN Scruff Group - SG Niedersachsen Group - SK Schieland Group - SL Schieland Group - SL Altena Group - AT Upper germanic Trias Group - RN Lower germanic Trias Group - RB Zechstein Group - ZE Upper Rotliegend Group - RO Lower Rotliegend Group - RV Limburg Group - DC Farne Group - CF Carboniferous Limestone Group - CL Old Red Group - OR Banjaard Group - OB Silurian - OS