684: TERTIARY VOLCANIC ROCKS. [Ch." XXXII. 



It appears from the species of shells collected principally by M. 

 Boue, and examined by M. Deshayes, that the fossil remains imbed- 

 ded in the volcanic tuffs, and in strata alternating with them in Hun- 

 gary, are of the Miocene type, and not identical, as was formerly sup- 

 posed, with the fossils of the Paris basin. 



CHAPTER XXXII. 



ON THE DIFFERENT AGES OF THE VOLCANIC ROCKS, Continued. 



Volcanic rocks of the Tertiary period, continued — Extinct volcanoes of Auvergne — 

 Mont Dor — Breccias and alluviums of Mont Perrier, with bones of quadrupeds — 

 River dammed up by lava-current — Range of minor cones from Auvergne to the 

 Vivarais — Monts Dome— Puy de Come — Puy de Pariou — Cones not denuded by 

 general flood — Lower Miocene volcanic rocks near Clermont — Hill of Gergovia — 

 Eocene volcanic rocks of Monte Bolca— Trap of Cretaceous period — Oolitic pe- 

 riod — New Red Sandstone period — Carboniferous period — " Rock and Spindle" 

 near St. Andrew's — Old Red Sandstone period— Silurian period — Cambrian pe- 

 riod — Laurentian volcanic rocks. 



Volcanic Rocks of Auvergne. — The extinct volcanoes of Auvergne 

 and Cantal, in Central France, seem to have commenced their erup- 

 tions in the Lower Miocene period, but to have been most active 

 during the Upper Miocene and Pliocene eras. I have already alluded 

 to the grand succession of events, of which there is evidence in Au- 

 vergne since the last retreat of the sea (see p. 228). 



The earliest monuments of the tertiary period in that region are 

 lacustrine deposits of great thickness (2, fig. 728, p. 686), in the low- 

 est conglomerates of which are rounded pebbles of quartz, mica- 

 schist, granite, and other non-volcanic rocks, without the slightest 

 intermixture of igneous products. To these conglomerates succeed 

 argillaceous and calcareous marls and limestones (3, fig. 728), con- 

 taining Lower Miocene shells and bones of mammalia, the higher 

 beds of which sometimes alternate with volcanic tuff of contempora- 

 neous origin. After the filling up or drainage of the ancient lakes, 

 huge piles of trachytic and basaltic rocks, with volcanic breccias, 

 accumulated to a thickness of several thousand feet, and were super- 

 imposed upon granite, or the contiguous lacustrine strata. The 

 greater portion of these igneous rocks appear to have originated dur- 

 ing the Upper Miocene and Pliocene periods ; and extinct quadru- 

 peds of those eras, belonging to the genera Mastodon, Rhinoceros, 

 and others, were buried in ashes and beds of alluvial sand and gravel, 

 which owe their preservation to overspreading sheets of lava. 



