Ch. XXXIL] puy de papjou. 691 



this is a bed of sand and gravel 3 feet thick, evidently an ancient 

 river-bed, now at an elevation of 25 feet above the channel of the 

 Sionle. ' This gravel, from which water gushes out, rests upon gneiss, 

 /, which has been eroded to the depth of 25 feet at the point where 

 the annexed view is taken. At d, close to the village of Les Combres, 

 the entrance of a gallery is seen, in which lead has been worked in 

 the gneiss. This mine shows that the pebble-bed is continuous, in a 

 horizontal direction, between the gneiss and the v.olcanic mass. Here 

 again it is quite evident, that, while the basalt was gradually under- 

 mined and carried away by the force of running water, the cone 

 whence the lava issued escaped destruction, because it stood upon a 

 platform of gueiss several hundred feet above the level of the valley in 

 which the force of running water 'was exerted. 



Puy de Pariou. — The brim of the crater of the Puy de Pariou, near 

 Clermont, is so sharp, and has been so little blunted by time, that it 

 scarcely affords room to stand upon. This and other cones in an 

 equally remarkable state of integrity have stood, I conceive, uninjured, 

 not in spite of then loose porous nature, as might at first be naturally 

 supposed, but in consequence of it. No rills can collect where all the 

 rain is instantly absorbed by the sand and scoriae, as is remarkably 

 the case on Etna ; and nothing but a waterspout breaking directly 

 upon the Puy de Pariou" could carry away a portion of the hill, so long 

 as it is not rent or engulfed by earthquakes. 



Hence it is conceivable that even those cones which have the fresh- 

 est aspect and most perfect shape may lay claim to very high an- 

 tiquity. 'Dr. Daubeny has justly observed, that had any of these vol- 

 canoes been in a state of activity in the age of Julius Caesar, that gen- 

 eral, who encamped upon the plains of Auvergne, and laid siege to its 

 principal city (Gergovia, near Clermont), could hardly have failed to 

 notice them. Had there been any record of their eruptions in the 

 time of Pliny or Sidonius Apollinaris, the one would scarcely have 

 omitted to make mention of it in his Natural History, nor the other 

 to introduce some allusion to it among the descriptions of this his 

 native province. This poet's residence was on the borders of the Lake 

 Aidat, which owed its very existence to the damming up of a river by 

 one of the most modern lava-currents.* 



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

 the Cantal, we can at present merely affirm, that they overlie the 

 Lower Miocene lacustrine strata of that country, which may be partly 

 Upper Eocene and partly Lower Miocene (see Map, p. 221). They 

 form a great dome-shaped mass, having an average slope of only 4°, 

 which has evidently been accumulated, like the cone of Etna, durino* a 

 long series of eruptions. It is composed of trachytic, phonolitic, and 

 basaltic lavas, tuffs, and conglomerates, or "breccias, forming a moun- 

 tain several thousand feet in height. Dikes also of phonolite, trachyte, 



* Daubeny on Volcanoes, p. 14. 



