234 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [DeC.19. 



MoNTS Dor and Cantal. 



That the name of craters of elevation should have been given to 

 large conical masses, in no part of which can any crater be discovered, 

 whether of denudation, or engulfment, or eruption, is a singular in- 

 stance of theoretical language, invented originally for distinct phse- 

 nomena, becoming applied to another set of conditions, which are only 

 in a small degree analogous. Although no craters are now discern- 

 ible on the summits of Mont Dor and the Cantal in Central France, 

 it is probable that they once possessed them, as I believe the greatest 

 number of eruptions to have proceeded from the highest part of each 

 mountain, where there is the greatest thickness of erupted lava and 

 ejected matter. At this central point and around it, where so large 

 a volume of basalt, trachyte, pumice, scoriae, and other materials, 

 whether solid or fragmentary, were emitted, the chief upheaval also 

 may doubtless have occurred, and the slope of the conical mass may 

 perhaps be greater now than it was originally. Yet as the average 

 inclination of the dome-shaped mass of the Cantal is only 4°, and 

 that of Mont Dor 8° 6', we may reasonably question, after stud^Hbig 

 Mr. Dana's description of the recent additions made to the flanks of 

 Mounts Loa and Kea, the one having a slope of 6° 30', the other of 

 7° 46', whether there is any real necessity for supposing, that the 

 basaltic currents of the French volcanos were at first more horizontal 

 than they are now. 



The advocates of the elevation-crater theory, having assumed that 

 the volcanic beds were in their origin almost horizontal, in Central 

 France, found it indispensable to imagine, that a large cavity pre- 

 existed in the granite, the lowest part of which coincided with what 

 is now the highest part of the dome. At length, to use an expression 

 of Ehrenberg in his paper on Volcanic Infusoria, " the concave beds 

 were converted into a convex dome," and this as usual is referred to a 

 paroxysmal effort of the subterranean force * . 



This subject has been so ably discussed, in the controversy between 

 MM. de Beaumont and Dufresnoy on the one side, and MM. Constant 

 Prevost and Yirlet on the other, that I need say no more on the sub- 

 ject. A closer observation of existing volcanos will decide whether the 

 truth lies between the opinions of the opposite schools, and whether 

 Messrs. Scrope, Constant Prevost, myself and others who have referred 

 these mountains to successive eruptions proceeding chiefly from a cen- 

 tral vent, have judged correctly, and how far we may have underrated 

 the elevatory force, of which the intensity would no doubt be greatest 

 at the point where the eruptive and injectmg forces have been most 

 energetic. That both the one and the other, however, have operated 

 gradually, and with intermittent violence, not by any single great par- 

 oxysm, I feel as convmced as ever. 



* Quart. Journ. Geol. Soc. vol. ii. p. 74, Memoirs. 



