Scrope's Memoir on the Geology of Central France, 



operations, might be in some degree assimilated to formations of doubt- 

 ful origin. With this view he extmined the district of Auvergne, covered 

 with extinct craters, the products of which are in contact not only with 

 primitive rocks, but with the tertiary and fresh water strata, or those which 

 .have been most recently formed. In June 1821 he established himself at 

 Clermont, and from this central point he made excursions through the vi- 

 cinity, transferring his head-quarters to the Baths of Mont D'Or, Le Puy, 

 and Aubenas. 



The result of this examination is given in two books, the first of which 

 treats of the geology of the interior of France, and the second of the vol- 

 canic formations. 



After treating in the first chapter of the first book of the prinjitive and 

 secondary formations, Mr Scrope discusses at considerable length, and 

 with great ability, the curious subject of the fresh water form-ations of 

 Central France. These are found to occupy three different districts on the 

 primitive plateau, and appear to have been deposited in as many distinct 

 and independent basins, viz. that of the Limagne, the Cantal, and the Haute 

 Loire. These three formations he attributes to the same era, both from 

 the similarity of their composition, and of the fossils which they contain. 

 " That of the Cantal alone," says he, " appears deficient in gypsum, but this 

 may be owing to the very small portion of it which lies open to observa- 

 tion. All are remarkable for containing highly siliceous beds. The forma- 

 tion of the Haute Loire distinguishes itself from the others in the circum- 

 stance that the limits of the lake basins in which its strata were deposited 

 remain obvious, so much so, that if the narrow gorges of La Voute and 

 Chamalieres were filled up, the lakes would be immediately restored near- 

 ly to what may be supposed their original level ; while the deposits of the 

 upper end of the Limagne and also of the Cantal are found at a height 

 which overlooks an extensive and low horizon, in which no traces of a for- 

 mer barrier can be perceived capable of containing a body of vpater accu- 

 mulated at that level, and we have consequently been forced to suppose 

 these strata to have sustained a considerable degree of elevation since 

 their deposition. The formation of the Limagne is remarkable for the 

 alternation of strata of compact pure raarl, which would seem to have 

 concreted from a pulpy mass in the manner of the chalk strata, or 

 the lower beds of shell marl in the Bakie Loch, described by Mr 

 Lyell, (GeoL Trans, vol. ii. No. 8. p. IQ-J with the beds containing the 

 indusia tubulata, which bear marks of a tedious and gradual formation, ana- 

 logous to that of stalagmites, and by their gravelly nature, and the cha- 

 racters of the fossils they inclose, appear to have formed the banks of a 

 marsh or river, generally dry, though occasionally overflowed, rather than 

 the bottom of a permanent lake." 



As the last fresh water of Auvergne, Mr Scrope classes the remarkable 

 deposit from which tripoli is extracted at Menat between Riom and' 

 Montatgn. It occupies the bottom of a circular basin about a mile in Alk» 

 meter, encircled by lofty primitive rocks, and emptying itself into the' 



