• The structures in Dedenborn and Bastogne are both of the same origin, and should be given the same name. The original term boudin was used first and it was a perfectly adequate name for these structures. Even today mullion and boudin are both used for these compressional structures. To end the confusion in terminology, we propose the consistent usage of mullion for all the structures described in this paper, based on the genetic definitions of the terms mullions and boudins given in recent structural geology textbooks.

• Mullions formed during the first phases of Variscan shortening as response to the mechanical structure of veined layers with the competence contrast (vein > psammite > pelite). Vein quartz was the strongest element of the system due to its coarse grain size and due to its CO2 - rich fluid content.

• Mullion shape in cross section is a potential gauge for paleo-rheology: It depends on the power law creep exponent n. Initial, highly simplified modelling indicates a value between 2 and 5. Further work using non-linear finite element models and detailed study of samples is in progress.

• At peak burial this part of the lower Devonian passive continental margin a regional scale vein set perpendicular to bedding was developed in a high fluid pressure cell.

• Basin inversion occurred sub-parallel to the extension direction in the continental margin, in an approximately 100 km wide zone.