262 EOCENE PERIOD. [Ch.XlX. 



crater of Etna, it may have formed an insignificant feature in 

 the great pile, and may frequently have been destroyed and 

 renovated. 



We cannot at present determine the age of the great mass 

 of Mont Dor, because no organic remains have yet been found 

 in the tuffs, except impressions of the leaves of trees of species 

 not determined. Some of the lowest parts of the great 

 mass are formed of white pumiceous tuffs, in which animal 

 remains may perhaps be one day found. In the mean time, 

 we conclude that Mont Dor had no existence when the grits 

 and conglomerates of the Limagne, which contain no volcanic 

 materials, were formed ; but some of the earliest eruptions 

 may perhaps have been contemporary with those described in 

 the commencement of this chapter. To the latest of these 

 eruptions, on the other hand, we refer those trachytic breccias 

 of Mont Perrier which were shown in the sixteenth chapter, p. 

 217, to alternate with Miocene alluviums. 



Velay. The observations of M. Bertrand de Done have not 



yet established that any of the most ancient volcanos of Velay 



were in action during the Eocene period, although it is very 



probable that some of them may have been contemporaneous 



with the oldest of the Auvergne lavas. There are beds of 



gravel in Velay, as in Auvergne, covered by lava at different 



heights above the channels of the existing rivers. In the 



highest and most ancient of these alluviums the pebbles are 



exclusively of granitic rocks; but in the newer, which are 



found at lower levels, they contain an intermixture of volcanic 



substances. We have already shown, in the sixteenth chapter, 



that, in the volcanic ejections and alluviums covered by the 



lavas of Velay, the bones of animals of Miocene species have 



been found, in which respect the phenomena accord perfectly 



with those of Auvergne. 



Plomb du Cantal. In regard to the age of the igneous 

 rocks of the Cantal we are still less informed, and at present 

 can merely affirm that they overlie the Eocene lacustrine strata 

 of that country. The Plomb du Cantal (see Map, wood-cut 



