The north-eastern border of France more or less follows the western limit of a large Hercynian massif that extends eastwards into Belgium, Luxemburg and Germany to form the complex Rhine highlands. It comprises several distinct sub-massifs from the Ardennes in the north, through the Hunsrük to the Saarland in the southeast. South of the Saarland, and also included in this chapter although not strictly a Hercynian massif, are the Vosges du Nord (hills developed in Triassic rocks). South of these, in Alsace, are the Vosges themselves, a Hercynian massif, mirror-imaging the Black Forest massif in southern Germany across the Rhine Rift Valley.