and on tlte Origin of the Valkys of' Auvergne, 215 



this would be requiring us to point out a cone which, though 

 elevated by volcanic agency, was destitute of any of the more 

 usual concomitants of such operations. 



But if Mr Lyell will be content to abandon this part of his 

 position, I shall not despair of presenting him with cases * which 

 fulfil the other conditions which he lays down as necessary to 

 establish the point. 



Mr Scrope, in page 74. of his Memoir on Central France, 

 has described " a circular lake, called Le Gour de Tazana, 

 about half a mile in diameter, and from thirty to forty feet 

 deep. Its margin for a fourth of the circumference is flat, and 

 elevated above the valley into which the lake discharges itself. 

 Every where else it is environed by steep granitic rocks, thickly 

 sprinkled with small scoriae and puzzolana, and rising about 200 

 feet from the level of the water. These fragments are all that 

 indicate the volcanic origin of this gulf-like basin, but they are 

 sufficiently decisive. No stream of lava, or even fragments of 

 any large size, are perceivable." 



Mr Scrope proceeds to remark, that this curious, and in 

 Auvergne rare, variety of crater, is identical in its characters 

 with some of the largest and most remarkable of the volcanic 

 maare in the Eyfel, particularly that of Meerfeld ; a crater 

 which I had myself noticed in my work on volcanos, and 

 which, according to the description there given, might be cited 

 as a case fulfilling all the conditions required by Mr Lyell ; 

 but which I do not bring forward as such, because I have no 

 right to prefer my own negative testimony, with regard to tjie 

 absence of igneous products, to Mr Scrope's positive statement 

 as to their occasional presence in it. It is, however, satisfactory, 

 in the instance I have here alleged, to have the authority of a 



• Von Buch and his disciples would also dte JJ)« dolomitic cones near 

 Trent as instances of isolated rocks uplifted by volcanic action, arid unac- 

 companied by volcanic products of the usual kind. 



The difficulty, however, of admitting that part of his theory which sup- 

 poses the penetration of an entire calcareous mountain with magnesia, in such 

 a manner as to constitute a chemical compound in atomic proportions, makes 

 mo hesitate as to the fact itself of their having been uplifted, though I per- 

 ceive that some geologists, who object to the elevation-theory, as applied to 

 the trachytes of Auvergne, appear to adopt it with reference to these. — See 

 Considerations on Voleanoes ; by Poulett Scrope^ Esq, See, Geol. Soc. Londony 1825, 

 p. 205, et seq. 



