A detailed study of the relationships between basements and lava flows gives the full meaning of the modifications due to the volcanic environment. Syneffusive thermal metamorphism is an exceptional event and posteffusive evolution of fossilized profiles consists of weak but typical chemical and mineralogical contaminations. This cryptoevolution is not effective enough for a sound granite trapped under a lava flow to be weathered. Consequently, weathering of the granites fossilized by lava flows happens before the effusion takes place, and the effusions maintain the profiles as they stand. Such profiles are real inherited weathering. Taking into account both the information delivered by fossilized weathered granites and the chronological data given by the lava flows, two families of weathering can be distinguished: Miocene profiles are half-way between fersiallitisation and ferruginisation; Plio-Pleistocene profiles are characterized by bisiallitisation. If each different climate of the Pliocene and of the Pleistocene does not lead to a specific kind of weathered granite, nevertheless the slope deposits fossilized during that period plead in favour of a cooling tendency. As far as erosion is concerned, it is clearly seen that wide spaces of the French Massif Central have undergone a slow evolution of the landforms from the Miocene to the present, as proved by the presence of different kinds of weathered granites on a same level. Nevertheless, local excavations can be heavy.
