688 TERTIARY VOLCANIC ROCKS. [Ch. XXXII. 



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

 of the volcanic cone called the Puy dc Tartaret, formed of loose sco- 

 riae, from the base of which has issued the lava-current before men- 

 tioned. The materials of the dam which blocked up the river, and 

 caused the Lac de Chambon, are also, in part, derived from a landslip 

 which may have happened at the time of the great eruption which 

 formed the cone. 



This cone of Tartaret affords an impressive monument of the very 

 different 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 

 ancient columnar trachyte and basalt, which once flowed at very high 

 levels from Mont Dor.* 



When we follow the course of the river Couze, from its source in 

 the lake of Chambon to the termination of the lava-current at 

 Nechers, a distance of thirteen miles, we find that the torrent has in 

 most places cut a deep channel through the lava, the lower portion of 

 which is columnar. In some narrow gorges the water has even had 

 power to remove the entire mass of basaltic rock, though, the work 

 of erosion must have been very slow, as the basalt is tough and hard, 

 and one column after another must have been undermined and re- 

 duced to pebbles, and then to sand. During the time required for 

 this operation, the perishable cone of Tartaret, composed of sand and 

 ashes, has stood uninjured, proving that no great flood or deluge can 

 have passed over this region in the interval between the eruption of 

 Tartaret and our own times. 



If we now return to the section (fig. 728), I may observe that the 

 lava-current of Tartaret, which has diminished greatly in height and 

 volume near its termination, presents here a steep and perpendicular 

 face 25 feet in height towards the river. Beneath it is the alluvium 

 No. 9, consisting of a red sandy clay, which must have covered the 

 bottom' of the valley when the current of melted rock flowed down. 

 The bones found in this alluvium, which I obtained myself, consisted 

 of a species of field-mouse, Arvicola, and the molar tooth of an ex- 

 tinct horse, Equus fossilis. The other species, obtained from the 

 same bed, are referable to the genera Sus, Bos, Oervus, Felis, Canis, 

 Martes, Talpa, Sorex, Lepus, Sciurus, Mus, and Lagomys, in all no 

 less than forty-three species, all closely allied to recent animals, yet 

 nearly all of them, according to M. Bravard, showing some points of 

 difference, like those which Mr. Owen discovered in the case of the 

 horse above alluded to. The bones also of a frog, snake, and lizard, 

 and of several birds, were associated with the fossils before enumer- 

 ated, and several recent land-shells, such as Cyclostoma elegans, Helix 

 hortensis, H. nemoralis, H. lapicida, and Clausilia rugosa. If the 



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

 tral France. 



