Erosion surface, slightly tilted to the East and which truncates the gneiss and granite of the Hercynian floor of the Cevannes. It is in fact a post-Hercynian erosion surface bearing superficial Triassic deposits. It is noticeably rejuvenated by the valley of the Chassezac and its tributaries. The floor has reacted to this rejuvenation as a homogenous mass, except for some harder seam that may be seen in the foreground. France Institut Geographique National. Relief form atlas, 1956, p. 101.