The southern border fault (Merens fault) of the Aston massif in the Pyrenees of Ariege, France, corresponds to a southward thrusting of this massif over a zone of sedimentary formations attributed to the Canaveilles series (probably Cambrian). On the south, these sediments are in fault contact with the Hospitalet gneiss massif (Pinet fault); farther east, toward Merens, they form the cover of the Hospitalet massif.