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 Brittany (; french: link=no, Bretagne ; br, Breizh, or ; Gallo: ''Bertaèyn'' ) is a peninsula, historical country and cultural area in the west of modern France, covering the western part of what was known as Armorica during the period ...

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 The Ordovician ( ) is a geologic period and system, the second of six periods of the Paleozoic Era. The Ordovician spans 41.6 million years from the end of the Cambrian Period million years ago (Mya) to the start of the Silurian Period Mya. T ...

, Silurian and Devonian rocks forming a part of the Variscan

orogen An orogenic belt, or orogen, is a zone of Earth's crust affected by orogeny. An orogenic belt develops when a continental plate crumples and is uplifted to form one or more mountain ranges; this involves a series of geological processes collecti ...

and include

sandstone Sandstone is a clastic sedimentary rock composed mainly of sand-sized (0.0625 to 2 mm) silicate grains. Sandstones comprise about 20–25% of all sedimentary rocks. Most sandstone is composed of quartz or feldspar (both silicates ...

quartzite Quartzite is a hard, non- foliated metamorphic rock which was originally pure quartz sandstone.Essentials of Geology, 3rd Edition, Stephen Marshak, p 182 Sandstone is converted into quartzite through heating and pressure usually related to tec ...

s and slates.Carte Geologique de la France, 1:1,000,000 scale, 5th edn, Bureau de Recherches Geologiques et Minieres The hills form a part of the border between the

départements A department (, ) is an administrative or political division in several countries. Departments are the first-level divisions of 11 countries, nine in the Americas and two in Africa. An additional 10 countries use departments as second-level div ...

Finistère Finistère (, ; br, Penn-ar-Bed ) is a department of France in the extreme west of Brittany. In 2019, it had a population of 915,090.

and

Morbihan Morbihan ( , ; br, Mor-Bihan ) is a department in the administrative region of Brittany, situated in the northwest of France. It is named after the Morbihan (''small sea'' in Breton), the enclosed sea that is the principal feature of the coastl ...

and just extend into Côtes-du-Nord.

References

Mountain ranges of Brittany Hills of France {{Brittany-geo-stub