Vol. 52.] LUSTRES ' OF MONT JO VET (SAVOY). 3 



This divergence of view is doubtless due in part to the fact that 

 the ' schistes lustres ' cover a considerable extent of country, and 

 the different theories rest on the interpretation of different sections. 

 Fortunately, however, Zaccagna x and Bertrand 2 have both recently 

 described Mont Jovet, and each claims that it supports the two 

 rival theories. 3 



Mont Jovet has long done service in geological controversy, as it 

 is situated close to Moutiers, where a school of mining nourished at 

 the beginning of the century. Its structure was investigated then, 

 and it has been repeatedly revisited. Pournet in 1849 claimed it 

 all as altered Jurassic ; while Lory, who worked over it with care, 

 identified the rocks of the central group of peaks as part of his 

 ' schistes lustres calcareo-talqueux du Qneyras et des vallees 

 piemontaises,' and therefore as Triassic. Favre, 4 who briefly de- 

 scribed the mountain in 1867, suggested that the limestones of this 

 series might be Jurassic. Zaccagna, like Lory, accepted the central 

 rocks as ; schistes lustres,' but he gave a section across the mountain, 

 showing a marked unconformity between these and both the Trias 

 and the Carboniferous. He therefore regarded the mountain as ' an 

 isolated outskirt of the Upper Archaean zone which rises through 

 the stratified rocks between the Isere and the Doron, and which, 

 being constituted of calc-schists, has been hitherto united to the 

 Triassic formation. It was probably part of the eastern covering of 

 the zone of lower crystalline schists which passes to Cevins, being 

 united in a synclinal to the calc-schists, which ought also to cover 

 the western side of the nucleus of the Vanoise.' 5 



Bertrand, on the contrary, describes the mountain as having 

 exactly the opposite structure. According to him it is ' un noyau 

 synclinal ouvert entre les deux branches etirees d'un meme pli 

 anticlinal' (op. cit. p. 100). Or, as he concludes elsewhere (p. 125), 

 although there are some uncertainties, ' there is no doubt that it is 

 impossible to claim that one can see there a Palaeozoic island, for it 

 is in fact a paquet of Lias, perhaps with Triassic schists at the base, 

 placed on the summit of the fan.' 



Practically the two observers simply invert the mountain. The 

 central rock which forms the summit, according to Zaccagna, is an 

 Archaean schist ; according to Bertrand, it is a Liassic limestone 

 identical, save for the absence of belemnites, with the adjoining 

 flags with Belemnites truncatus (op. cit. p. 124). According to 

 Zaccagna the rocks of the summit are an island, on the flanks of 

 which the Triassic and Carboniferous beds were unconformably 

 deposited; according to Bertrand the rocks of the summit were 



1 D. Zaccagna, ' Riassunto di Osservazioni geologiche fatte sul versante 

 occidentale delle Alpi Graie,' Boll. R. Com. geol. Ital. vol. xxiii. (1892) 

 pp. 229-231, 396-397. 2 M. Bertrand, op. jam cit. 



3 For an abstract of these two papers, see J. W. Gregory, * Recent Contri- 

 butions to the Geology of the Western Alps,' Science Progress, vol. hi. (1895) 

 pp. 147-174. 



4 A. Favre, ' Recherches geologiques flans les parties de la Savoie, du 

 Piemont et de la Suisse voisines du Mont Blanc,' vol. iii. (1867) pp. 230-231. 



5 Zaccagna, op. cit. (1892) p. 397, & pi. v. sect. 2. 



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