Professor Forbes on the Geology of Auvergne. IJJ 



of successively imposed coats of lava trickling down in an in- 

 clined position, was assumed subsequently to the horizontal de- 

 position of those beds, by a thrust upwards from below ; hence 

 such an external configuration may be independent of the vol- 

 canic nature of the materials. Cavities so formed are what Von 

 Buch terms Craters of Elevation. Tiie recently published in- 

 genious views of M. Elie de Beaumont, on the epochs and 

 modes of elevation of mountain chains, includes the theory of 

 Von Buch as a particular case, namely, an elevation at a point 

 producing a group^ instead of elevation along a line producing 

 a chain of mountains. Hence the groups of Mont Dor and the 

 Cantal have excited the particular attention of that very dis- 

 tinguished geologist, who, (with M. Dufrenoy), has published a 

 paper * expressly on the subject, which was my constant com- 

 panion whilst examining that country. The great excitement 

 which has recently prevailed amongst geologists, especially on 

 the Continent, about this matter, led me to examine the evi- 

 dences with the more attention, though my examination was 

 curtailed extremely by the constant annoyance of bad weather, 

 which I experienced in September last. 



What is brought forward as the chief novelty in the general 

 views of MM. Elie de Beaumont and Dufrenoy, is the actual 

 calculation of the spaces or fissures which should be left in the 

 slope of the cone (or rather pyramid of many sides). That 

 such spaces must occur is obvious, from the circumstance that 

 the surface of a cone is larger than its base, and that the ma- 

 terials, which when united occupied only the area of the base, 

 are to be elevated towards a common vertex. Looking upon 

 the question mathematically, nothing can be clearer or more sa- 

 tisfactory than such a statement ; and perhaps there is room for 

 regret, that, in the paper alluded to, a parade of analytical re- 

 search appears, which adds neither to the conclusiveness nor to 

 the elegance of the reasonings. The effect, however, of this 

 novelty, cannot fail to be advantageous to geological science. 

 It will give to geologists, in some cases, the means of reducing 

 to definite trial vague trains of reasoning, and it will generally 

 aid in fortifying the prosecutors of this speculative science with 

 • Annales des Mines, 2de Serie, torn. iii. 



