The Armançon rises 2 km (1.2 mi) north-west of Meilly-sur-Rouvres in the district known as the Auxois, on the lip of the saucer represented by the Paris Basin.

Its source is on the Lower Jurassic rocks where they and the Upper Triassic are much influenced by the granites and volcanism of the Morvan, a northward extension of the Massif Central.

Near Buffon, north-west of Montbard, the canal joins it again from the Brenne valley accompanied by the Dijon to Paris (Gare de l'Est) railway.

However, the Upper Jurassic rocks are available to supply the clay element of the materials for the cement works which lie between the river and the canal between Pacy-sur-Armançon and Lézinnes.

The Lower Cretaceous is comparable with the rocks of the Weald of southern England and the Upper Jurassic with the Oxford Clay and associated strata of the English Midlands.