ON THE VAKIOLITIC KOCKS OF MONT GENEVRE. 321 



Zaccagna*, however, agrees that the "massa diabasica" of 

 Mt. Genevre is intercalated in the calc-schists below the limestones 

 of Mt. Chaberton. He states that various authors have treated the 

 mass as Permian ; but against this view he urges that the calc- 

 schists cover it upon the French or western side. It is clear, how- 

 ever, that this reasoning, and that of other Italian geologists, will 

 only hold good if we regard the series as sedimentary. Moreover, 

 Zaccagna himself would seem to assign an eruptive origin to the 

 diabase-groups of the Val de Chabriere and of Mt. Genevre. 



The age of the calc-schists themselves has not been satisfactorily 

 determined. As early as 1850 Fournetf pointed out the existence 

 of this zone of the " roches penuines " at Mt. Genevre, and suggested 

 that they were of Carboniferous or earlier age. Lory :]:, selecting 

 the band of " Gypse et cargneules " below Clavieres as the top of the 

 Trias, included in that system the mass of the " schistes lustres 

 calcareo-talqueux " and much of the " pietre verdi " of Gastaldi. 

 Though strongly opposed by Italian writers, he issued a sketch-map 

 in 1881, in which the base of the Trias is still carried out to meet 

 the ancient gneisses along a line as far east as Susa §. This seems 

 a logical consequence of the acceptance of any part of the " schistes 

 lustres " as Triassic ; and in almost his latest scientific utterance he 

 affirmed the accuracy of these views ||. 



Notwithstanding his great breadth of vision, the balance of recent 

 evidence seems in this matter opposed to Lory. Zaccagna, for 

 example, states that the zone which he regards as Permian, and 

 which underlies dolomitic limestones with Gi/roj)oreUa, was deposited 

 in inequalities of the calc-schist series ^ ; and in his section of the 

 Pointe de Mary he shows an unconformity of the most decided cha- 

 racter between the two **. 



Zaccagna and Mattirolo, indeed, in the beautiful map appended to 

 the paper cited tt, carry their Triassic rocks from the frontier to 

 Brianeon, entirely excluding the Lias from the neighbourhood 

 of Mt. Genevre. Strips of Permian appear above the. diabase 

 group and on Mt. Chaberton. 



Gastaldi hesitated to divide up definitely the " Calcaire du Prian- 

 gonnais " of Lory ; but on the frontier itself his map Jj, if more 

 detailed, would probably agree with that of Zaccagna. We have 



* " Sulla geologia delle Alpi occidentali," Boll. R. Comit. geol. d'ltalia, xviii. 

 1887, p. 388. Cf. ibid. p. 377. 



t " Notes suY line excursion dans les Alpes en 1849," Ann. des sciences phys. 

 et nat. Lyon, 2^ ser. t. iii. (1850-51) p. 37. 



I " rescript, geol. du Daupbine," 1864, paragraphs 256 and 286, Bull. Soc. 

 Stat. Isere, 2^ ser. t. vii. pp. 14 & 72 ; " Stratigraphie des Alpes Graies et 

 Cottiennes," Bull. Soc. geol. France, 3= ser. t. i. (1873) p. 278. Cf. ibid. 

 p. 269. 



§ Bull. Soc. geol. France, 3' sdv. t. ix. p. 655. 



II " Etudes sur les schistes crystallins," Congres geol. internat. London, 1888, 

 pp. 2() and 28. 



% Boll. E.. Comit. geol. d'ltalia, vol. xviii. (1887) p. 389. 



** Ibid. tav. ix. 



tt Ibid. tav. xi. 



IJ Mem R. Accad, dei Lincei, ser. 3, vol. ii. tav. ii. 



