552 TERTIARY VOLCANIC ROCKS. [Ch. XXXH 



Hence it is conceivable that even those cones which have the freshest 

 aspect, and most perfect shape, may lay claim to very high antiquity. 

 Dr. Daubeny has justly observed, that had any of these volcanos been 

 in a state of activity in the age of Julius Cassar, that general, who en- 

 camped 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 Si- 

 donius 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.* 



Vela y. — The observations of M. Bertrand de Doue have not yet es- 

 tablished that any of the most ancient volcanos of Velay were in action 

 during the Eocene period. There are beds of gravel in Velay, as in 

 Auvergne, covered by lava at different heights above the channel 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, and which originated when the valleys had been 

 cut to a greater depth, an intermixture of volcanic rocks has been ob- 

 served. 



At St. Privat d' Allier a bed of volcanic scoriae and tuff was discovered 

 by Dr. Hibbert, inclosed between two sheets of basaltic lava ; and in 

 this tuff were found the bones of several quadrupeds, some of them 

 adhering to masses of slaggy lava. Among other animals were Rhino- 

 ceros leptorhinus, Hyaena spelsea, and a species allied to the spotted 

 hyaena of the Cape, together with four undetermined species of deer. 

 The manner of the occurrence of these bones reminds us of the pub- 

 lished accounts of an eruption of Coseguina, 1835, in Central America 

 (see p. 521), during which hot cinders and scoriae fell and scorched to 

 death great numbers of wild and domestic animals and birds. 



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

 tal, we can at present merely affirm, that they overlie the (Upper ?) Eocene 

 lacustrine strata of that country (see Map, p. 195). They form a great 

 dome-shaped mass, having an average slope of only 4°, which has evi- 

 dently been accumulated, like the cone of Etna, during a long series of 

 eruptions. It is composed of trachytic, phonolitic, and basaltic lavas, 

 tuffs, and conglomerates, or breccias, forming a mountain several thou- 

 sand feet in height. Dikes also of phonolite, trachyte, and basalt are 

 numerous, especially in the neighbourhood of the large cavity, probably 

 once a crater, around which the loftiest summits of the Cantal are 

 ranged circularly, few of them, except the Plomb du Cantal, rising far 

 above the border or ridge of this supposed crater. A pyramidal hill, 

 called the Puy Griou, occupies the middle of the cavity.f It is clear 

 that the volcano of the Cantal broke out precisely on the site of the 

 * Daubeny on Volcanos, p. 14 

 ■j- Mem. de la Soc. Geo!, de France, torn. i. p. 175. 



