Visiting the UK is on the whole a nice experience, except for the reoccurring practical joke ‘I wanted to come up with five famous Belgians but stranded at Tintin’. Beware, former EU friends, you are forgetting Max Lohest.

While the great nations of the world are busy with nothing more than proving that they are great, smaller ones focus on important aspects. In Belgium, food is highly ranked on that list. Let’s travel back in time to the days when you could walk up to a train, flash your hammer to show that you’re a geologist meaning business, and demand the train to stop at a particular road cut. You would do that with a couple of colleagues, having carefully planned an outcrop at walking distance from an excellent restaurant. After all, field observations need to be discussed and digested without delay, and colleagues need to be turned into friends.

One such field trip, on Monday 31st of August 1908, would go down in history. This was the fourth day of a six-day field trip throughout the Ardennes, attended by about forty geologists. That day they broke with the tradition of hijacking a train and instead got off like normal passengers at the railway station of Cowan. The report describes in poetic French how the group marvelled at the sunny weather, so contrasting with the stormy conditions during the night, before setting out to Benonchamps for a beautiful day of hiking across the area of Bastogne. The pinnacle of the day was a remarkable geomanifestation: a set of strangely shaped quartzitic layers deformed into elongated barrels. The excursion leaders, in particular Max Lohest, had already agreed on a name for this new feature. They would, soon worldwide, be called ‘boudins’ formed by the process of ‘boudinage’, even if no one knew what that actually entangled.

But it was a good name, and everyone immediately felt happy and hungry. From then on, geologists would look at those rocks, and associate them with the carefully arranged sausages on display at the butcher shops. The original report doesn’t reveal, but I’m sure that the end of the day was a celebration of boudins with boudins. It must have been that way, after all, that is how Belgium does geology, and conquers the world. Bastogne became the world-type locality for boudins for a very long time.

The concept was well understood throughout continental Europe but seemed to confuse geologists in Britain and America. The origin of the problem was finally pinned down in 1961 by Wilson, who compared how sausages were displayed. The standard practice of arranging sizeable sausages side by side, as is dictated by geology, was apparently not custom in England or its colonies. There, strings of tiny sausages were fabricated and hung end-to-end. Clearly, an unnatural custom that needs to be abandoned.

Also on the scientific side, history took an unexpected and unfortunate turn. Structural geologists pride themselves that since Ramsay in 1967, they are possibly the only modern scientists among geologists, keeping description and interpretation strictly apart. But 60 years earlier, in Bastogne, this was already well understood by that famous group of visionaries that came up with food-based names, paying only attention to morphology, and reserving the discussion on genesis for dinner.

But they were too early, way ahead of their time, and could not be understood. In a discussion that lasted about a century, the meaning of boudins changed. Every geologist today knows them as extensional structures, because that is what all the textbooks say. And that is why the boudins in their type locality, are not longer considered as being boudins. An ending that is both sad and wrong.

Let me therefore conclude with two things. First, I demand that our boudins are restored and respected. We defined them first, don’t break what you borrow.

And second, I hereby declare the 31st of August as national day of geology, with boudins for all. That goes for Belgium, and all other nations with a taste for appetite.

Kris Piessens
GSB – Geological Survey of Belgium

Main sources or worth reading

Kenis, I. 2004. Brittle-Ductile Deformation Behaviour in the Middle Crust as Exemplified by Mullions (Former “Boudins”) in the High-Ardenne Slate Belt, Belgium. Aardkundige Mededelingen vol. 14, Leuven University Press, Leuven, Belgium. 127 pp. ISBN 90 5867 445 2.

Lohest, M., Stainier, X. and Fourmarier, P., 1909. Compte rendu de la session extraordinaire de la Société Géologique de Belgique, tenue à Eupen et à Bastogne les 29, 30 et 31 août et le 1, 2 et 3 septembre 1908. Annales de la Société géologique de Belgique, 35: 8351-8434.

Ramsay, J.G. 1967. Folding and fracturing of rocks. McGraw-Hill, 1st edition. 568 p.

Urai, J. L., Spaeth, G., van der Zee, W., & Hilge, C. (2001). Evolution of mullion (formerly boudin) structures in the Variscan of the Ardennes and Eifel. Journal of the Virtual Explorer, 3(January). https://doi.org/10.3809/jvirtex.2001.00027

Vanbrabant, Y., & Dejonghe, L. (2006). Structural analysis of narrow reworked boudins and influence of sedimentary successions during a two-stage deformation sequence (Ardenne-Eifel region, Belgium-Germany). Memoirs of the Geological Survey of Belgium, 53, 1–43.

Wilson, G. (1961). The tectonic significance of small scale structures, and their importance to the geologist in the field. Annales de La Société Géologique de Belgique, 84, 423–548.

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