and on the Origin of the Valleys of Auvergne. 209 



would explain the regularity of their form, their perfectly de- 

 tached and isolated position, and their occurring each in the 

 midst of a sort of amphitheatre composed of volcanic rocks of a 

 totally different description. 



Diluvial action here will not assist us, for had the domitic hills 

 alluded to been the fragments of a continuous stratum or coulee 

 once extending along the line in which they occur, some vestiges 

 of the rock in question would be found in the intervening 

 spaces, as well as for some distance beyond the hills that are 

 placed at either extremity of the range ; neither would the cra- 

 ters of the surrounding rocks, which must in many cases be pre- 

 sumed to be of greater antiquity, have remained undestroyed by 

 a current of water which acted with sufficient force and conti- 

 nuance to reduce the Puy de Dome to its present conical form. 



The ordinary action of water is still more inadequate to the 

 effect supposed, for the whole of the table-land on which these 

 mountains repose, consists of volcanic matter of soporous adescrip- 

 tion,that scarcely adrop of water rests upon its surface, and nearly 

 the whole which falls from the heavens sinks down into the 

 soil, until it finds an exit in the Valley of Royat beneath, a little 

 way from the city of Clermont. 



The only other hypothesis is that of Mr Scrope *, who sup- 



• Mons. Lecoq, the director of the museum at Clermont, who, from his 

 general intelligence, no less than from his particular acquaintance with the 

 geological structure of Auvergne, deserves to be listened to in a case of this 

 kind, has published, in the *"• Annales Scientifiques de I'Auvergne," an account 

 of these donritic cones, accompanied with a theory of their formation, differ- 

 ing in some respects from that of Von Buch, but at the same time totally 

 opposed to the one which Mr Scrope has advocated. He argueii that the 

 appearances which he describes, imply the action of water as well as of fire ; 

 the first being indicated not only by the rolled fragments intermixed with 

 the domite itself, but also by an alluvial deposit which covers it in many 

 places, as, for instance, on the summit of the Great Cliersou ; the latter by 

 the crystals of glassy felspar, fer oligiste, &c., as well as by the position, 

 form, &.C. of the mountains themselves. To reconcile these two facts, he sup- 

 poses the domite to have constituted a part of that great tufaceous deposit 

 which is seen at Boulade, near Iss )ire, and which has doubtless been derived 

 from the trachyte of Mont Dor, This, after having been spread on the sides 

 of the latter chain by the oj)eration of water, he imagines to have been in 

 these points uplifted by the volcanic action which took place beneath it, to 

 which cause must be attributed the crystals of glassy felspar, and the other 

 indications of fire which the rock presents. A curious confirmation of this 



