^4 :^^\^i^X>auhenyontheBiIuvhlTh<^Gri'^ 



J !^OdMr instances are, howevcsTj-giveniirt which the amcmttt of 

 the excavation has been as much as 70 feet, and in the Viva- 

 rais it is stated as still mope considerable. Yet even here there 

 must be allowed to be a wide distance between what the rivers 

 ard proved to have effected, and the depth to which mawyivalleys, 

 attributed on all hands to the operation of water, are seen to 

 penetrate into the rocks which bound them. 

 in iR^fpuglu we to leaves Qutirely out of the account the /fact, 

 i:that no excavation bearings any great resemblance to the general 

 iibrm and width of our valleys, has been shewn to have resulted 

 ;^from the action of the present rivers in Auvergne, All the in- 

 l^tances adduced seem to be of narrow and abrupt ravines, which 

 are strikingly distinguished from the easy and gradual slope of 

 t$ke valleys, at the bottom of which they are found ; and though 

 it may be contended, that, when the ravine had been worked to 

 a certain depth, varying according to the nature of the rock, it 

 would become undermined, and in this manner be graduallv 

 widened, until it acquired the shape and dimensions of an ordi- 

 nary valley ; yet it seems singular that, if the post-diluvial lavas 

 :Qf Auvergne are of the antiquity supposed, and if the ordinary 

 effect of rivers is to produce in course of time such valleys, no 

 instance should have been pointed out presenting a nearer re- 

 semblance to those of other countries, than the ravines depicted 

 in Mr Scro{)e''s volum^jp^w riil9 



This geologist, however, goes on to shew, that the valleys in 

 Auvergne cannot have been formed by the action of a deluge, 

 jjilecause the. ancient, or, as I have called them, the ante-diluvial 

 jieurrents, are not all found nearly about the same general level, 

 ju-i*' Had the valleys,"'* he contends, "been excavated by any 

 one simultaneous cause, the lava-currents, which had flowed 

 ■yito the fresh water basin, would be found nearly, if not alto- 

 gether, at one uniform level, and ruch as had flowed since at 

 another nearly uniform level. Now, instead of this, the cur- 

 ^jrents are found at all elevations, from 1500 to 15 feet above 

 the present water-channel."" 



But Mr Scrope appears here to have forgotten what he had 

 himself before established in his section of Gergovia, namely, 

 that the fresh- water limestone went on forming after the voU 

 canos had begun their eruptions. 



