The Montagnes Noires ( French, 'black mountains'), also known as the Montagne Noire ( French, 'black mountain') and in

Breton Breton most often refers to: *anything associated with Brittany, and generally ** Breton people ** Breton language, a Southwestern Brittonic Celtic language of the Indo-European language family, spoken in Brittany ** Breton (horse), a breed **Ga ...

as Menez Du are an east–west oriented range of hills in

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

centred on the town of

Gourin Gourin (; br, Gourin) is a commune in the Morbihan ''département'' of Brittany in north-western France. Geography Gourin is in the northwest of Morbihan, northeast of Quimper and northwest of Lorient. Historically, it belongs to Cornouaill ...

. 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 The Precambrian (or Pre-Cambrian, sometimes abbreviated pꞒ, or Cryptozoic) is the earliest part of Earth's history, set before the current Phanerozoic Eon. The Precambrian is so named because it preceded the Cambrian, the first period of the ...

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

Silurian The Silurian ( ) is a geologic period and system spanning 24.6 million years from the end of the Ordovician Period, at million years ago ( Mya), to the beginning of the Devonian Period, Mya. The Silurian is the shortest period of the Paleozo ...

and

Devonian The Devonian ( ) is a geologic period and system of the Paleozoic era, spanning 60.3 million years from the end of the Silurian, million years ago (Mya), to the beginning of the Carboniferous, Mya. It is named after Devon, England, whe ...

rocks forming a part of the

Variscan The Variscan or Hercynian orogeny was a geologic mountain-building event caused by Late Paleozoic continental collision between Euramerica (Laurussia) and Gondwana to form the supercontinent of Pangaea. Nomenclature The name ''Variscan'', comes f ...

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 Tectonic uplift, uplifted to form one or more mountain ranges; this involves a series of geological pr ...

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 tect ...

s and

slate Slate is a fine-grained, foliated, homogeneous metamorphic rock derived from an original shale-type sedimentary rock composed of clay or volcanic ash through low-grade regional metamorphism. It is the finest grained foliated metamorphic rock. ...

s.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 coastli ...

and just extend into Côtes-du-Nord.

References

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