Jean Jung; Zoneographie et age des formations cristallophylliennes des massifs hercyniens francais [with discussion]. Bulletin de la Société Géologique de France ; S6-III (4-6): 329–343. doi: https://doi.org/10.2113/gssgfbull.S6-III.4-6.329
Two types of metamorphic series can be distinguished in the Hercynian (Paleozoic) massifs of France--the Auvergne-Vosges type, grading conformably into a Paleozoic cover, and the Pyrenean-Armorican-Limousin type, overlain unconformably by Devonian and Dinantian (Carboniferous) beds. The stratigraphic relations and metamorphic zoning are studied with respect to the orogenesis of the Hercynian chain. It is concluded that the former type represents cores formed during early Cambrian orogenic activity; the latter type, in ranges peripheral to these cores, was evolved more or less late in the Paleozoic.