Montagnes Noires

The Montagnes Noires (French, 'black mountains'), also known as the Montagne Noire (French, 'black mountain') and in Breton as Menez Du are an east-west oriented range of hills in Brittany centred on the town of Gourin. They culminate in the peak of Roc de Toullaeron (Breton: Roc'h Toull-al-Laeron)
which attains a height of either 318m or 326m. Other significant peaks include Ar Menez (304m) and Montagne Noir (307m) (or, in Breton: Menez Du).
They are composed from a range of Precambrian, Ordovician, Silurian and Devonian rocks forming a part of the Variscan orogen and include sandstones, quartzites and slates.
The hills form a part of the border between the départements of Finistère and Morbihan and just extend into Côtes-du-Nord.