This range is also a watershed and a border between the Atlantic and Mediterranean climates. The geological substrate consisting of granite, limestone and schist is an additional cause of diversity. Natural and human dynamics are conditioned by terrain, geology and climate.
Three rock types: granite, schist and limestone
©
Thomas Kleitz
Limestone
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©
Thomas Kleitz
Schist
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Sombre or shiny schist forms the ridges and ledges of the Cévennes, delineates the hamlets, terraces and bridges, and offers up its acidity to the great sweet-chestnut orchards.
Majestic limestone covers the great cliffs of the Causses and gorges, sculpted hallucinatory rock shapes above ground and in chasms, and shaped the stones found in clapas (piles of stones gathered while clearing land for planting) and the vaults of sheep barns.
On the slopes of Mont Lozère and Mont Aigoual, granite felsenmeer provide the enormous blunted blocks used for menhirs, pens and the grey walls of hamlets.
Two contrasting climates
The Mediterranean climate is characterised by violent storms in spring and autumn. It has very strongly influenced the built landscape of the Cévennes. Water is both a precious source of life – rare and difficult to retain on schist slopes – and a destructive force to be feared during the great cataclysmic storms.
To the West and North of the watershed, the climate gradually takes on an Atlantic rainfall pattern, with finer rains that are more evenly spread over the course of the year.
Water: the alchemy of climate and substrate
The great rounded mountains tops of Mont Lozère stock surplus rainwater in their sands and thus regulate a vast network of streams. Waterlogged areas and peat bogs are characteristic of this massif.
The Causse limestone absorbs all rain water. Waterways are entirely absent from the surface of the Causse, which suffers from a chronic lack of water. Water filters through to the subterranean karstic networks and re-emerges through a series of springs at the foot of the cliffs.