70 EXTINCT VOLCANOS OF CENTRAL FRANCE AND OTHER COUNTRIES. 



of Desmarests 1 , were all barely adequate to establish truths, which are now universally 

 recognised, and have been rendered familiar to the British public by the beautifully il- 

 lustrated work of our countryman Poulett Scrope 2 . The Eifel 3 in Germany has since 

 been shown to be a tract in most respects analogous to Auvergne, while in Iceland 

 are combined nearly all the phenomena which can be required to convince us, not only 

 of the similarity of modern and ancient volcanic eruptions, but also of the great extent 

 to which such phenomena have prevailed within the historic sera 4 . Besides these well- 

 known European tracts, other quarters of the globe, particularly the continent of South 

 America and its adjacent islands, abound in examples of the varied phenomena of vol- 

 canic action. In Asia Minor the district called the Catececaumene, described by 

 Strabo, and recently visited by Mr. Hamilton and Mr. Strickland, presents an exact 

 analogy with the volcanic regions of central France and the Eifel, &c. But Auvergne 

 is not merely replete with analogies to modern volcanic regions ; it was further found 

 to contain many rocks, which, though from their characters they must have been 

 formed by igneous agency, are yet in many lithological features dissimilar from 

 modern lavas, whilst they resemble many of the so-called trap rocks. Thus, for 

 example, though many of the " lava currents" in the valleys of Auvergne are undi- 

 stinguishable from those of Etna and Vesuvius, other currents, equally traceable to 

 lips of craters, are composed of prismatic basalt very similar to the basalts of the 

 Giant's Causeway or of the Hebrides ; and pitchstone, that ancient form of obsidian, a 

 mineral product so abundant in some existing volcanos, has been added to the list of 

 analogies 5 . The district further presents numberless examples of other masses, of 

 nearly similar composition, trachytes, ancient basalts, clinkstone, &c, some of which 

 are undistinguishable from our British trap rocks, arranged in great tabular masses at 

 various altitudes on the mountain sides. These, unlike the more modern currents, are 

 not traceable to distinct vents of eruption, and are in fact but the remnants of once ex- 

 tensive lava currents, which had flowed over the surface of this tract before the forma- 

 tion even of the present river courses. By such evidences, therefore, the inquirer is 



1 Carte Topographique et Mineralogique du Puy de Dome. Paris, 1823. 



2 Scrope's Geology of Central France. London, 1825. 



5 See Hibbert's History of the extinct Volcanos of the Basin of Neuwied, 1832. 



4 See Travels in Iceland, by Sir G. Mackenzie, Bart., and Drs. Holland and Bright; also LyelFs Principles 

 of Geology, where the author gives a vivid portraiture of the magnitude of the modern Icelandic lava currents. 



5 See Lyell and Murchison " On the Excavation of Valleys in Central France, Edin. Phil. Mag., July, 1829, 

 p. 15. Obsidian occurs in vast quantities at the Isle of Ascension. It would appear that this substance is also 

 very abundant in parts of Asia, where its presence had not previously been recognised, as between Anni and 

 Kars, for example, at a great distance from the coast. Mr. W. I. Hamilton has recently passed through that 

 region, and thus expresses himself concerning it : "I had always imagined, that the accounts of mountains and 

 palaces of glass belonged only to such fables as the Arabian Nights. To day, however, I passed over the foot 

 of a mountain of glass, and where the roads were paved with the same material. It was in fact Obsidian, or 

 Volcanic glass, most perfect and uniform in its texture." (Letter to his Father dated June 30, 1836.) 



