Ch. XXXIL] volcanoes of AUVERGNE. 687 



wliicli it is clear that the surface of No. 3 formed at that period the 

 lowest level at which the waters then draining the country flowed. 

 Next in age to this basaltic platform comes a patch of ochreous sand 

 and gravel (No. 5), containing many bones of quadrupeds. Upon 

 this rests a pumiceous breccia or conglomerate, with angular masses 

 of trachyte and some quartz pebbles. This deposit is followed by 5 b 

 (which is similar to 5) and 5 c similar to the trachytic breccia 5 a. 

 These two breccias are supposed, from their similarity to others found 

 on Mont Dor, to have descended from the flanks of that mountain 

 during eruptions ; and the interstratined alluvial deposits contain the 

 remains of mastodon, rhinoceros, tapir, deer, beaver, and quadrupeds 

 of other genera, referable to about forty species, all of which are ex- 

 tinct. I formerly supposed them to belong to the same era as the 

 Miocene faluns of Touraine ; but more recent researches seem to show 

 that they ought rather to be ascribed to the older Pliocene epoch. 



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

 which inhabited the country when the formations 5 and 5 c orig- 

 inated. Probably they were drowned during floods, such as rush 

 clown the flanks of volcanoes 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 sud- 

 denly melted by lava, causing a deluge of water to bear clown frag- 

 ments of igneous rocks mixed with mud to the valleys aud plains 

 below. 



It will be seen that the valley of the Issoire, clown which these 

 ancient inundations swept, was first excavated at the expense of the 

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

 after w T hich it was reexcavated 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 Boulade, from which a great many other Newer Pliocene 

 mammalia have been collected by MM. Bravard and Pomel. Among 

 these, the Elephas primigenius, Rhinoceros tickorinus, Deer (including 

 reindeer), Equus, Bos, Antelope, Felis, and Canis were included. 

 Even this deposit seems hardly to be the newest in the neighborhood, 

 for if we cross from the town of Issoire (see fig. 728) over Mont Per- 

 rier to the adjoining valley of the Couze, we find another bone-bed 

 (No. 9) overlaid by a current of lava. 



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 bar- 



