Oh. XXXIL] MONT DOE, AUVERGNE. (Jg5 



In Auvergne, the most ancient and conspicuous of the volcanic 

 masses is Mont Dor, which rests immediately on the granitic rocks 

 standing apart from the freshwater strata.* This great mountain 

 rises suddenly to the height of several thousand feet above the sur- 

 rounding platform, and retains the shape of a flattened and somewhat 

 irregular cone, all the sides sloping more or less rapidly, until their 

 inclination is gradually lost in the high plain around. This cone is 

 composed of layers of scoriae, pumice-stcnes, and their fine detritus, 

 with iuterposed beds of trachyte and basalt, which descend often in 

 uninterrupted sheets until they reach and spread themselves round 

 the base of the mountain.f Conglomerates, also, composed of angu- 

 lar and rounded fragments of igneous rocks, are observed to alter- 

 nate with the above ; and the various masses are seen to dip off 

 from the central axis, and to lie parallel to the sloping flanks of the 

 mountain. 



The summit of Mont Dor terminates in seven or eight rocky peaks, 

 where no regular crater can. now be traced, but where we may easily 

 imagine one to have existed, which may have been shattered by 

 earthquakes, and have suffered degradation by aqueous agents. Orig- 

 inally, perhaps, like the highest crater of Etna, it may have formed 

 an insignificant feature in the great pile, and may frequently have 

 been destroyed and renovated. 



According to some geologists, this mountain, as well as Vesuvius, 

 Etna, and all large volcanoes, has derived its dome-like form not from 

 the preponderance of eruptions from one or more central points, but 

 from the upheaval of horizontal beds of lava and scoriae. I have ex- 

 plained my reasons for objecting to this view in Chapter XXIX., 

 when speaking of Palma, and in the " Principles of Geology." J The 

 average inclination of the dome-shaped mass of Mont Dor is 8° 6', 

 whereas in Mounts Loa and Kea, before mentioned, in the Sandwich 

 Islands (see fig. 693, p. 623), the flanks of which have been raised by 

 recent lavas, we find" from Mr. Dana's description that the one has a 

 slope of 6° 30', the other of 1° 46'. There is therefore no reason 

 whatever for imagining, as some have supposed, that the basaltic cur- 

 rents of the ancient French volcano were at first more horizontal than 

 they are now. Nevertheless it is possible that during the long series 

 of eruptions required to give rise to so vast a pile of volcanic matter, 

 which is thickest at the summit or centre of the dome, some disloca- 

 tion and upheaval took place ; and during the distension of the mass, 

 beds of lava and scoriae may, in some places, have acquired a greater, 

 in others a less inclination, than that which at first belonged to them. 



Respecting the age of the great mass of Mont Dor, we cannot come 

 at present to any positive decision, because no organic remains have 



* See the Map, p. 221. 



f Scrope's Central France, p. 98. 



% See chaps, xxiv., xxv., and xxvi., 7th, 8th, and 9th editions. 



