1.2.7. La Roche Formation - LAR
Authors: Dewalque, 1874; Asselberghs, 1946; Godefroid & Stainier, 1982.
Description: At the stratotype, from the bottom to the top, the La Roche Formation is made up of:
· 200 m of dark blue slates with thin layers of light blue sandstones or quartzites. Load casts;
· 100 m of dark blue slates and blue grey silty slates with sandy intercalations and 0.1-1 m thick banks of reddish sandstones. Rare fossils;
· 150 m of dark blue slates progressively richer to the top in thin sandy layers and blue green siltstones, sometimes fossiliferous.
Stratotypes: Lower boundary at La Roche-en-Ardenne, along the Hotton road; upper boundary S of Jupille, at the Hodister crossing.
Area:S and SE sides of the Dinant Synclinorium, up to the vicinity of the Xhoris fault.
Thickness: 215 m S of Couvin, 420 m S of Grupont, about 400 m at Amonines, 400 m at the northern flank of the La Roche Syncline increasing to > 800 m at the southern flank of the syncline.
Age: Probably Pragian, due to the age of the neighbouring formations.