Causse is an Occitan word which means limestone plateau, the geology formed by erosion via the chemical dissolution of layers of soluble limestone. Surface water is very limited because the rain that falls drains away quickly, finding its way into fissures thereby creating subterranean passages. In this limestone country the rivers run deep underground.
The land is rugged, often with the bedrock exposed on the surface in the form of a limestone pavement. It is criss-crossed by dry stone walls and covered in small oaks, maples of Montpelier and juniper. In spring wild daffodils, snowdrops and purple orchids appear. In winter the spiky-leaved fragon can serve as a decorative substitute for holly which cannot be found on limestone soils.
Distinctive surface features include rocky uplands suitable only for sheep farming and hunting, dry valleys known as combes with relatively fertile soil suitable for growing cereals or vegetables, potholes, and deep circular or elliptical depressions known as dolines. Dolines can vary in depth from several metres to hundreds of meters, with fertile soil in the bottom.
The sheep here are a special, hardy breed, called Caussenardes. They appear to wear 'lunettes' or dark glasses. Goats also abound in the area, and a special small, round, white cheese called a 'cabecou' is the local speciality. An "appellation controlée" cabecou is known as a "Rocamadour".
The population density is low and in the past there was very little light pollution in the area but this is changing as villages install street lighting and illuminate various historic buildings with spotlights. However, it is still possible on a clear moonless night to see a sky packed full of stars. The Milky Way is spectacular in summer, and satellites such as the International Space Station are highly visible as they pass over, illuminated by the sun.
The causse is typical of the landscape of Quercy, covering approximately two-thirds of the department. The Parc naturel régional des Causses du Quercy has been created to safeguard and promote this natural resource.
The causse of Gramat stretches from the river Dordogne southwards towards Cahors. On the north side of the river, the limestone area around Martel is known as the causse of Martel and extends northwards beyond Cressensac and almost to Brive. A sign on the Autoroute A20 "Le causse Corrèzien" marks the edge of the causse just south of Brive. The three principal causses of Quercy are the causse of Gramat, the causse of Limogne/Lalbenque and the causse of Saint-Chels.
A swallow hole or aven, a typical feature, is often very deep and in the shape of an upturned funnel with steep sides, opened on the surface of the limestone by erosion and leading to underground caves and streams. The major site of the gouffre de Padirac is formed from a swallow hole where the ground underneath has collapsed forming a deep cylindrical hole in the ground, connected to passages leading to an underground stream. The water from the gouffre of Padirac travels westwards underground until it emerges at the foot of the cliffs in Montvalent and runs into the river Dordogne.
Lacs de Saint-Namphaise are watering holes or ponds carved in big solid slabs of limestone on the surface of the plateau. There are hundreds of such watering holes on the causses of Quercy, named after an officer of Charlemagne who abandoned the war to live the life of a hermit on the causses where, according to legend, he dug these watering holes. Generally rectangular in form they are fed by rainwater and rarely by a spring. In a region where water is rare they are indispensable for the life of humans and their livestock.
These days the lacs de Saint-Namphaise are used less by herds of sheep. But they are still essential for wildlife, such as small mammals and birds who come to drink, bathe and feed. Many species of reptiles, amphibians and insects reproduce and frequent these valuable sources of water.