Ch. XIX.] MINOR VOLCANOS OF AUVERGNE. 263 



No. 56) is a conical mass, which has evidently been formed, 

 like the cone of Etna, by a long series of eruptions. It is 

 composed of trachytic and basaltic lavas, tuffs, and conglo- 

 merates, or breccias, forming a mountain several thousand feet 

 in height. This volcano evidently broke out precisely on the 

 site of the lacustrine deposit before described (Chapter xvii.), 

 which had accumulated in a depression of a tract composed of 

 micaceous schist. In the breccias, even to the very summit 

 of the mountain, we find ejected masses of the fresh-water 

 beds, and sometimes fragments of flint, containing Eocene 

 shells. Deep valleys radiate in all directions from the central 

 heights of the mountain, especially those of the Cer and Jour- 

 danne, which are more than twenty miles in length, and lay open 

 the geological structure of the mountain. No alternation 

 of lavas with undisturbed Eocene strata have been observed, 

 nor any tuffs containing fresh-water shells ; on the northern 

 side of the Plomb du Cantal, at La Vissiere, near Murat, we 

 have pointed out on the Map (wood-cut, p. 226) a spot where 

 fresh-water limestone and marl are seen covered by a thickness 

 of about 800 feet of volcanic rock. Shifts are here seen in the 

 strata of limestone and marl *. 



Although it appears that the lavas of the Cantal are more 

 recent than the fresh-water formation of that country, it does 

 not follow that they may not belong to the Eocene period. 

 The lake may possibly have been drained by the earthquakes 

 which preceded or accompanied the first eruptions, but the 

 Eocene animals and plants may have continued to exist for a 

 long series of ages, while the cone went on increasing in 

 dimensions. 



Train of minor Volcanos. We shall next consider those 

 minor volcanos before alluded to, which stretch in a long range 

 from Auvergne to the Vivarais, and which appear for the 

 most part to be of newer origin than the mountains above 

 described. They have been thrown up in a great number of 

 isolated points, and much resemble those scattered over the 



* See Lyell and Murchison, Ann, des Sci. Nat., Oct. 1829. 



