ROOM III. GEOLOGICAL PHENOMENA OF AUVERGNE. 355 



nearly twenty miles in length, and two in breadth. The 

 highest point of this chain is the Puy de Dome, which is 

 4,000 feet above the level of the sea, and is entirely composed 

 of volcanic matter ; it has a regular crater which is 300 feet 

 deep, and nearly 1,000 feet in circumference. 



The volcanic vents of Central France are of very different 

 ages ; some being of immense antiquity, whilst others are 

 evidently of comparatively recent origin, for they have exploded 

 through ancient beds of basalt : but even the most modern of 

 the craters and lava streams, belong to a period very remote 

 in relation to the present condition of the country. 



In the plains, and on the flanks of the volcanic mountains, 

 and rising into hills of moderate elevation, are a series of 

 fresh- water strata, with alternations of scoriae, basalt, &c. based 

 on the foundation rocks of granite and gneiss. The lowermost 

 oeds are for the most part composed of clay, sand, and breccia, 

 without organic remains. The next in order are fresh-water 

 tertiary limestones and calcareous marls, in nearly horizontal 

 strata, amounting in total thickness to 900 feet. It is in 

 these beds that the mammalian remains we have to notice 

 occur : they are associated with lacustrine and fluviatile shells, 

 as potamides, planorbis, helix, limnea, &c. and terrestrial 

 plants. In some localities there are beds of gypseous and 

 iaminated marls, and intercalations of siliceous limestones ; in 

 other areas, the limestone has an intermixture of volcanic 

 matter, and presents the characters of a sediment tranquilly 

 deposited in a lake, into which ashes and scorise were showered 

 Tom a neighbouring volcano. 



The fresh-water limestones are in many places covered by 

 thick beds of basalt and scorise, and the summits of the lower 

 aills composed of these strata are capped by basaltic lava. The 

 Drift, or alluvial sand and gravel, contains bones of mastodons, 

 elephants, hippopotami, &c. as in other countries of Europe ; 

 and the more modern superficial soil abounds in remains of 

 dogs, hares, beavers, bears, &c. 



EOCENE AND MIOCENE MAMMALIA. The mammalian re- 

 mains from this region have been referred to three very 

 distinct geological epochs ; ! viz. : 



1 See Sir Charles Lyell, " Proceedings of the Geol. Society," 1845, 

 p. 75. 



