548 yoLCANOS of AUVERGNE. [Ch. XXXIl 



whether they may not rather be ascribed to the older Phocene epoch is 

 a question which farther inquiries and comparisons must determine. 



Whatever be their date in the tertiary series, they are quadrupeds 

 which inhabited the country when the formations 5 and 5 c originated. 

 Probably they were drowned during floods, such as rush down the flanks 

 of volcanos during eruptions, when great bodies of steam are emitted 

 from the crater, or when, as we have seen, both on Etna and in Iceland 

 in modern times, large masses of snow are suddenly melted by lava, causing 

 a deluge of water to bear down fragments of igneous rocks mixed with 

 mud, to the valleys and plains below. 



It will be seen that the valley of the Issoire, down which these an- 

 cient inundations swept, was first excavated at the expense of the for- 

 mations 2, 3, and 4, and then filled up by the masses 5 and 5 c, after 

 which it was re-excavated before the more modern alluviums (Nos. 6 and 

 7) were formed. In these again other fossil mammalia of distinct species 

 have been detected by M. Bravard, the bones of an hippopotamus having 

 been found among the rest. 



At length, when the valley of the Allier was eroded at Issoire down 

 to its lowest level, a talus of angular fragments of basalt and freshwater 

 limestone (No. 8) was formed, called the bone-bed of the Tour de Bou- 

 ladcj from which a great many other mammalia have been collected by 

 MM. Bravard and Pomel. In this assemblage the Eleplias primigenius 

 Rhinoceros ticJiorinus, Deer (including rein-deer), Equus, Bos, Antelope, 

 Fells, and Cam's, were included. Even this deposit seems hardly to be 

 the newest in the neighbourhood, for if we cross from the town of Issoire 

 (see fig, 676) over Mont Perrier to the adjoining valley of the Couze, 

 we find another bone-bed (No. 9), overlaid by a current of lava (No. 10). 



The history of this lava-current, which terminates a few hundred 

 yards below the point No. 10, in the suburbs of the village of Nechers, 

 is interesting. It forms a long narrow stripe more than 13 miles in 

 length, at the bottom of the valley of the Couze, which flows out of a 

 lake at the foot of Mont Dor. This lake is caused by a barrier 

 thrown across the ancient channel of the Couze, consisting partly of the 

 volcanic cone called the Puy de Tartaret, formed of loose scorise, from 

 the base of which has issued the lava-current before mentioned. The 

 materials of the dam which blocked up the river, and caused the Lac de 

 Chambon, are also, in part, derived from a land-slip which may have 

 happened at the time of the great eruption which formed the cone. 



This cone of Tartaret afi'ords an impressive monument of the very 

 difierent dates at which the igneous eruptions of Auvergne have hap- 

 pened ; for it was evidently thrown up at the bottom of the existing 

 valley, which is bounded by lofty precipices composed of sheets of an- 

 cient columnar trachyte and basalt, which once flowed at very high levels 

 from Mont Dor.* 



* For a view of Puy de Tartaret and Mont Dor, see Scrope's Volcanos of Cen- 

 tral France. 



