CONTENTS. INTRODUCTORY ACCOUNT OF THE NOTICES WHICH HAVE BEEN § 1. The Volcanic Mountain-Its general Outline-Conglomerates. § 2. Structure - Central Peaks - Trachytic Plateaux - Clinkstone § 3. Recent Eruptions. 1. Mont Mezen: vast Currents of Clinkstone and Basalt-- 2. More recent Eruptions-Subsequent Excavation of Valleys- 234 247 Plate. LIST OF ILLUSTRATIONS. VI. Valley of Villar and Plateau of Prudelle X. Montagne de Bonnevie (a cluster of Basaltic Columns), XII. Basaltic Plateaux of the Coiron (Ardêche), from the XIV. Valley of Montpezat (Ardêche) XV. La Coupe d'Ayzac (Ardêche) XVII. Profiles and Sections, &c. XIII. Volcanic Cone and Basaltic Lava-current of Jaujac (Ardêche) V. The Southern Chain of Puys, from the Puy de la Rodde VII. Valley of the Dordogne and Mont Dore, from the Puy Gros on the North IX. The Valley of Chambon and the Mont Dore from the East XI. Panoramic Sketch of the Basin of Le Puy (Haute Loire) and of the Mont Mezen, taken from the Mont d'Ours XVI. Sections of Granitic Plateau from East to West and from N.N.E. to S.S.W... At the end of the Volume. GEOLOGY AND EXTINCT VOLCANOS OF CENTRAL FRANCE. CHAPTER I. GRANITIC PLATEAU AND MARINE STRATIFIED FORMATIONS. THE parallel of 46:30, passing near the towns of Châteauroux and Châlons-sur-Saône, will be found to divide France into two nearly equal portions, of which the northern may be considered as a vast plain, whose waters flow gently towards the north and west through the Seine and the lower Loire. South of this line the surface continues to rise with a gradual slope, so as to form an inclined plane, which progressively acquires an elevation of more than 3000 feet above the sea in the Auvergne and Forèz, and a still greater in the Gevaudan and Vivarais, where it reaches the height of 5500 feet. Here it is abruptly cut down by the deep valley of the Rhone, which, running nearly due north and south, separates it from the ranges east of that river, in the departments Drôme, Isère, and Hautes Alpes. On the south-west also this high ground rapidly descends through broken and irregular embranchments to the basin of the Gironde. It may, in fact, be considered as a triangular B |