Brittany
Geology

The Breton peninsula appeared during the Cadomian Orogeny, which formed its northern coastline, between Guingamp and Fougères. The southern part emerged during the Hercynian orogeny. At the same time, an intense volcanic activity left large quantities of granite. Between the Cadomian and Hercynian periods, the region was submerged several times and the sea left fossils and sedimentary rocks, mostly schist and sandstone. Because of the absence of limestone, soils in Brittany are usually acid.

The Armorican massif straightened and flattened several times during the formation of the Pyrenees and the Alps. Changes in sea levels and climate led to a strong erosion and to the formation of more sedimentary rocks. Metamorphism is responsible for the distinctive local blue schist and for the rich subsoil of the Groix island, which comprises glaucophane and epidote.

During the Quaternary glaciations, Brittany was covered by loess and rivers started to fill the valleys with alluvial deposits. The valleys themselves were a result of a strong tectonic activity between the African and the Eurasian plate. The present Breton landscape did not acquire its final shape before one million years ago. The Breton subsoil is characterised by a huge amount of fractures that form a large aquifer containing several millions square meters of water.
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