534 PfiOCEEDINGS OF THE GEOLOGICAL SOCIETY. [Feb. 2, 



posed of beds of trachyte and basalt, alternating with their conglo- 

 merates, show angles of elevation of only from about 4° towards 

 the base, to 8° near the summits, of these mountain masses. But 

 this is likewise just about the average angle of descent of the recent 

 lava- streams of the Puys. The latter, by the admission of De 

 Beaumont and Dufrenoy, owe their slope to fluidity alone. If, as 

 these same authorities contend, the former owe their inclination to 

 sudden upheaval alone, having been previously horizontal, surely the 

 coincidence of the average angles of inclination of the two classes 

 of lavas (which, too, are often placed side by side, and slope in the 

 same direction, only at different heights, for considerable distances 

 from their several eruptive vents) would be miraculous ! That such 

 identical effects can have proceeded from such opposite causes in so 

 many contiguous instances is wholly incredible ; and the supposition 

 is contrary to the laws of philosophical reasoning. Besides, why do 

 we not find the upheaved lava-beds at angles of 50°, 70°, or 90° ? 

 why not vertical ? Why do they always affect just that moderate 

 amount of angular elevation, neither more nor less, that is charac- 

 teristic of the lavas which have admittedly flowed in the open air, 

 and close to them, only from more recently-opened vents of eruption? 

 A direct proof, indeed, that the old basaltic beds which cover the 

 slopes of the Mont Dore and Cantal have flowed down them as lavas, 

 is found in the fact that they are all traceable up to some high 

 point where more or less of scoriae and bombs show that the current 

 of lava had its eruptive source. 



Without following this branch of the subject into further detail, 

 for which there is no space here — ^nor, as I conceive, any need — I 

 may say, in a word, that, interpreted by the ordinary laws of volcanic 

 action, the history of the volcanic remains of Central Prance is clear 

 and intelligible — the Mont Dore, Cantal, and Mezen being in this 

 view the skeletons of three great eruptive volcanos, like Etna or 

 Teneriffe, which have been subjected to a vast amount of atmospheric 

 degradation since the extinction of their central fires, and perhaps 

 have shared to some extent in a general elevation of the whole 

 district; while from numerous iadependent vents, along or near the 

 same N. and S. line of presumed subterranean fissure, other single 

 eruptions from time to time took place, resembling those of Lanzarote 

 and the other chains of miaor volcanos so often seen in the vicinity of 

 great volcanic mountains. On the contrary hypothesis, that these 

 mountains were severally produced by sudden upheaval, while the 

 cones and currents of the independent vents, or at least of the more 

 recent among them, were simply eruptive, which is the theory of 

 MM. de Beaumont and Dufrenoy, the history of this district be- 

 comes an unintelligible chaos, as wholly irreconcileable with its 

 visible phenomena as the theory itself is with the normal processes 

 of volcanic energy witnessed ia localities where it is still in activity. 



It is satisfactory to know that M. Constant Prevost and M. Cordier, 

 both of whom at first had countenanced the upheaval doctrine in 

 reference to the extinct volcanos of Central France, whoUy renounced 

 and discarded the idea after visiting and carefully examining the 



