1845.] LYELL ON LAVA CURRENTS IN AUVERGNE. 77 



by the fall of masses of lava from the cliff above. On the whole, 

 therefore, if we take the Puy de Tartaret and its lava as a type of the 

 products of the most modern volcanoes of Auvergne, we may infer, 

 from the facts above described, that the latest eruptions occurred at 

 the close of the Newer Pliocene, if not in the Post- pliocene period, 

 or when the mollusca were identical with those now living, although 

 a great many of the mammalia belonged to species now extinct. 



Section from the Valley of the Couze at Nechers, through Mont Perrier and Issoire to the Valley 

 of the AUier, and the Tour de Boulade, Auvergne. 



Couze R. Mont Perrier. Issoire. Tour de Boulade. 



10. Lava current of Tartaret near its termination at Nechers. 



9. Bone-bed, red sandy clay under the lava of Tartaret. 



8. Bone-bed of the Tour de Boulade. 



7. Alluvium newer than No. 6. 



6. Alluvium with bones of hippopotamus. 



5 c. Trachytic breccia resembling 5 a. 



5 b. Upper bone-bed of Perrier, gravel, &c. 



5 a. Pumiceous breccia and conglomerate, angular masses of trachyte, quartz pebbles, &c. 



5. Lower bone-bed of Perrier, ochreous sand and gravel. 



4 a. Basaltic dyke. 



4. Basaltic platform. 



3. Upper freshwater beds, limestone, marl, gypsum, &c. 



2. Lower freshwater formation, red clay, greensand, clay, &c. 



1. Granite. 



A. At a point corresponding to this, and situated on the north side of the hill of Gergovia, the 

 Melania inquinata has been found in freshwater marl under basalt. 



In the accompanying section I have shown at the north-west ex- 

 tremity the position occupied in the valley of the Couze at Nechers 

 by the lava of Tartaret, No. 10, and subjacent bone-bed No. 9. I 

 have at the same time shown, in the prolongation of the same sec- 

 tion to the hills on the right bank of the Allier, near Issoire, the 

 position of various other superficial deposits in which MM. Croizet, 

 Bravard, Pomel and others have detected mammalian remains be- 

 longing each of them to very distinct assemblages of species, and 

 which have doubtless originated at successive tertiary epochs. In 

 the oldest freshwater tertiary beds, Nos. 2 and 3, the Pal(Eotherium, 

 Anoplotherium, Anthracotherium, Didelphis, Crocodile, and other 

 genera common to the Paris basin, have been found associated with 

 species of Ehinoceros, Cervus, and some other genera, which, in 

 Cuvier's experience, had never been met with together in the same 

 formation. Above these rests a sheet of basalt, No. 4, forming the 

 north-west portion of the summit of Mont Perrier. In many places 

 similar elevated basaltic platforms rest on gravel-beds, in which 

 fossil mammalia have been detected. Next in age are the trachytic 

 and pumiceous breccias and accompanying gravel-beds, 5, 5 a, 

 5 b, 5 c, which were described by Sir K. Murchison and myself in a 

 paper published in 1829 in the Edinburgh New Philosophical Jour- 

 nal for July. In the alluvial deposits 5 and 7, bones have been ob- 

 tained belonging to the genera Mastodon (2 species), RhinoceroSy 



