See also: Geology of the Massif Central
The earliest geological traces can be dated to about 550 million years ago. In this period of the early Cambrian, the Massif Central seems to have been part of a large sill system separating two seas. Ablation debris is preserved here, partly interbedded with granitic intrusions. In the Ordovician, in the period from about 480 to 440 million years ago, a trench deepened and widened to form a broad ocean, in which mainly thick layers of clayey deep-sea sediments were deposited. 420 million years ago, at the threshold of the Silurian to the Devonian, Gondwana moved closer to central Europe again. Most of the seafloor was subducted and some of the sedimentary cover was also shifted. With that a huge fold mountain range, the Variscan Mountains, rose. It stretched across the entire (today's) eastern edge of North America, which at that time bordered Europe, across central to eastern Europe, and was probably much more immense than today's Alps. Sediments were transported to great depths and metamorphosed. Magma rose at the subduction zone.
As soon as the Variscan mountains rose, they already began to erode. Massive layers of debris were deposited in the foreland, which the meandering rivers turned into a swamp. This took place in the Carboniferous. Vast lush Carboniferous forests developed in this swamp. Coal layers were formed in these areas.
With the Alpine folding in the Tertiary, a second uplift of the terrain occurred: The collision of the African plate with the Eurasian plate caused seabed, on which limestone layers several hundred metres thick had formed, to be pushed upwards again along with the granite basement. These limestone plateaus form today's Causses, the geologically younger regions of the Massif Central. These were mainly formed in the Mesozoic period - especially in the Jurassic period - and rise in a staircase from northwest to southeast: While in Périgord and Quercy they reach only about 200 metres in height and are therefore not counted as part of the Massif Central proper, in the Lozère department they are over 1000 metres high. Several rivers, in particular the Tarn, have carved gorges of enormous depth between them.
Along a terrain collapse in the north, the Limagne, lava came to the surface again in the late Tertiary. These volcanoes, now extinct, form a mighty chain of steep basalt peaks west of Clermont-Ferrand, the so-called Chaîne des Puys. The most famous volcano is the Puy de Dôme, which gave the department its name.
