Professor Forbes on the Geology of Auvergne. 19 



Cantal and Mont Dor, is a fact so indisputable as to render the 

 argument about craters of elevation to a great extent merely 

 verbal. It is impossible to look upon either of these districtK, 

 and especially the latter, without perceiving incontrovertible 

 evidence of extensive convulsions. These convulsions could not 

 have taken place without elevation, and elevation is a kind of 

 action with which all geologists are familiar, and which has been 

 repeatedly appealed to by some of the warmest opponents of the 

 elevation craters. If this be an assumption then, it is a reason- 

 able one ; and the only other postulate of that theory, namely, 

 the extensive horizontal beds of volcanic matter, is so entirely 

 conformable to the facts observed in the comparatively level 

 ground adjoining these very mountain groups, as in fact to be 

 viewed as no assumption at all, or at least as possessed of equal 

 probability with any other opinion as to its primitive position. 

 I allude to the immense plateaux of basalt in the level country 

 of Auvergne, so faithfully and admirably delineated in Mr 

 Scrope^s work. There seems, therefore, so much of probability, 

 and so little of extravagance, in the theory, that we wonder how 

 it could possibly have given rise to such animated opposition. 



At the same time, looking on the subject with the impartiali- 

 ty of a spectator, — a mere straggler into the domains of geology, 

 it seems perhaps not less unreasonable to expect that all cases of 

 such actions should yield themselves with equal facility to the 

 support of so simple a hypothesis. Whilst we see in the Can- 

 tal an example of elevation of great unity and simplicity, the 

 Mont Dor, though bearing no less obvious traces of upheaving 

 agency, seems to bid defiance to any thing like regular analysis. 

 To attempt to calculate, on the principles of M. Elie de Beau- 

 mont, the magnitude of the fissured spaces produced by three 

 simultaneous (or consecutive) elevations at as many points with- 

 in a radius of three or four miles, appears unwarrantably bold. 

 Nor are the rugged features of this picturesque country trans- 

 latable into language sufficiently definite to authorize or to 

 disprove such a conclusion. I own that an unbiassed and most 

 attentive survey of the bearings of the group from the Pic de 

 Sancy (the highest ground in Central France, 1887 metres 

 above the sea) did not lead me to this conclusion, — I mean that 

 three such elevations were necessary and sufficient to explain the 



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