Oh. XXXIL] puy de c6me. 689 



animals were drowned by floods, which accompanied the eruptions of 

 the Puy de Tartaret, they would give an exceedingly modern geologi- 

 cal date to that event, which must, in that case, have belonged to the 

 end of the Newer Pliocene, or, perhaps, to the Post-pliocene period. 

 That the current which has issued from the Puy de Tartaret may, never- 

 theless, be very ancient in reference to the events of human history, 

 we may conclude, not only from the divergence of the mammiferous 

 fauna from that of our day, but from the fact that a Roman bridge of 

 such form and construction as continued in use down to the fifth cen- 

 tury, but which may be older, is now seen at a place about a mile and 

 a half from St. Nectaire. This ancient bridge spans the river Couze 

 with two arches, each about 14 feet wide. These arches spring from 

 the lava of Tartaret, on both banks, showing that a ravine precisely 

 like that now existing, had already been excavated by the river through 

 that lava thirteen or fourteen centuries ago. 



In Central France there are several hundred minor cones like that 

 of Tartaret, a great number of which, like Monte Nnovo, near Naples, 

 may have been principally due to a single eruption. Most of these 

 cones range in a linear direction from Auvergne to the Vivarais, and 

 they were faithfully described so early as the year 1802, by M. de 

 Montlosier. They have given rise chiefly to currents of basaltic lava. 

 Those of Auvergne called the Monts Dome, placed on a granitic plat- 

 form, form an irregular ridge (see fig. 624, p. 594), about 18 miles in 

 length and 2 in breadth. They are usually truncated at the summit, 

 where the crater is often preserved entire, the lava having issued from 

 the base of the hill. But frequently the crater is broken down on one 

 side, where the lava has flowed out. The hills are composed of loose 

 scoria?, blocks of lava, lapilli, and pozzuolana, with fragments of tra- 

 chyte and granite. 



Puy de Come.. — The Puy de Come and its lava-current, near Cler- 

 mont, may be mentioned as one of these minor volcanoes. This con- 

 ical hill rises from the granitic platform, at an angle of between 30 a 

 and 40,° to the height of more than 900 feet. Its summit presents 

 two distinct craters, one of them with a vertical depth of 250 feet. 

 A stream of lava takes its rise at the western base of the hill instead 

 of issuing from either crater, and descends the granitic slope towards 

 the present site of the town of Pont Gibaud. Thence it pours in a 

 broad sheet down a steep declivity into the valley of the Sioule, filling 

 the ancient river-channel for the distance of more than a mile. The 

 Sioule, thus dispossessed of its bed, has worked out a fresh one 

 between the lava and the granite of its western bank ; and the excava- 

 tion has disclosed, in one spot, a wall of columnar .basalt about 50 feet 

 high.* 



The excavation of the ravine is still in progress, every winter some 

 colamns of basalt being undermined and carried down the channel of 



* Scrope's Central France, p. 60, and plate. 

 44 



