L'Age des derniers Volcans de la France

Abstract

THE volcanic outbursts of Auvergne are to a certain extent disconnected locally and different in age. The western group is the more linear in arrangement, the eastern the more sporadic. In the one, the broad mass of the Cantal sends off a short spur—Aubrac—to the south-east, and a long one to the north, which extends through the famous Mont Dore district and terminates in the chain of Puys west of Clermont-Ferrand; in the other group we have the noted chain of the Velay and the outlier of Mezenc, Megal, and Coirons. The eruptions, apparently, were the latest to begin in the first of these districts, and the latest to cease in the region of the northern Puys. The tuffs and other sedimentary deposits, which are associated with the lava flows and masses of coarser scoria, have furnished palæontological data which fix the age of some of the volcanic outbursts, and make it possible by a comparative study of the ejecta to synchronise the discharges in different districts. The materials oscillate from basalts to andesites, with fairly abundant phonolites in two areas, and occasional rhyolites and trachytes among some of the older rocks. The earliest outbursts occurred in the Upper Miocene. Volcanic activity ceased in one of the southern extremities with the Lower Pliocene, in another with the Middle, in the Cantal itself with the Upper. It was prolonged in four districts well into the Quaternary, the date of its cessation being still far from certain.