Geology

170 million years of shaping from the water and the wind

Averyron’s current geology was formed more than 170 million years ago when the sea still covered the region. During this time there was a tropical climate, and the sea covered what was to become the Causse Noir, similar to the atolls of the Pacific. The warm and deep waters shelter an algae and coral reef in which many sponges, molluscs, sea urchins and crustaceans thrive.

It took 10 million years for the remains and skeletons of these organisms to cover the seabed until a 300-metre thick layer of limestone was created from these remains settling at the bottom of the ocean.

Let’s go back 100 million years: The Alpes and the Pyrenees are starting to form. At the bottom of the sea the rocks endure extreme forces. The limestone layers resist, bend and eventually fracture.

These fractures then create parallel faults, similar to the crevasse and serac fields that we can see on glaciers today.

80 million years later, the Grands Causses formation is steadily rising, with the sea having disappeared from the region.

Due to the slow and strenuous rise from the bottom of the ocean, the limestone rock made up of sediments of marine organisms is webbed with scars, making it less dense and more permeable. Water can circulate through these cracks, triggering the corrosion of the Causse Noir. The weathering process of the elements makes the existing passages wider and transforms them into roads, passageways, walls and cirques creating the architectural layout of la Cité de Pierres.

In order to understand and observe Aveyron’s fascinating geological history in the heart of the Causse Noir, la Cité de Pierres offers 10 staggering viewpoints overlooking the Causses and the Dourbie gorges.  You can visit la Cité de Pierres at Montpellier-le-Vieux in many ways - find out how to come and explore the city.