An ancient Caledonian lineation separating the crystalline mass of Scandinavia and Russia from the fragmented crustal blocks of the remainder of north-western Europe. This NW–SE trending structural feature complements the major Caledonian faults of northern Scotland (Great Glen Fault, Highland Boundary Fault, etc.). The Fennoscandian Border Zone has been active since that time, and in the Mesozoic formed the boundary between the stable, crystalline basement of Sweden and the Baltic and the subsiding Danish–Polish Furrow and North Sea Basin to the south-west. It is a complex zone of faults, horsts, and half-grabens which are best seen in southern Sweden (Scania), on the Danish island of Bornholm, and in southern Poland.