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. The Bornant enters from the left slightly lower. They all pass through forested country on Middle Jurassic geology. Shortly after, they pass into the department of Yonne. Near the border between the departments and just below Ravières, the river passes onto the Upper Jurassic where the valley bottom has accumulated Holocene alluvium. 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. Still in forested country, it passes the small town of Tonnerre and passes very briefly through the department of Aube as it flows onto the lower Cretaceous rocks, clothed in less woodland.