Vol. 50.] GNEISSES IN THE COTTIAN SEQUENCE. 233 



to the north of the Col de Traversette and runs from Monte Granero 

 through Punta Manzol and Punta Agugliassa to Punta Plengh. 

 This explanation does not, however, apply to the north-and-south 

 ridges that form the main features in what Mr. Coolidge aptly 

 describes ' as " the very tangled and little known ranges around 

 Cesanne." 



A comparison of the Eastern with the Western and Northern 

 Cottians reveals several points of much interest. Thus the two 

 latter are simple topographically and complex geologically ; they 

 include rocks of very different ages and characters, from the Upper 

 Mesozoic or Eocene diabases of Le Chenaillet and the Jurassic lime- 

 stones of Monte Chaberton to the old eruptives of Monte Viso ; they 

 have been upraised by earth-movements of considerable complexity, 

 involving extensive foldings, inversions, and overthrust faults. The 

 Eastern chain, on the other hand, is complex and inconspicuous topo- 

 graphically, having been cut across by the valleys of the Waldenses ; 

 but it is comparatively simple geologically. It is composed essentially 

 of a series of schists and schistose rocks — possibly bent into an anti- 

 clinal, with a series of banks of coarse fresh augen-gneiss occurring 

 along the axis of the fold. 



It has been generally agreed that the rocks of the Eastern Cottians 

 may be grouped into three series, a fundamental Laurentian gneiss 

 (the ' central gneiss ' of Zaccagna 2 ) at the base, covered by a double 

 set of schists, the Upper and Lower Archaean schists of Prof. Bonney 3 ; 

 these three correspond to the ' gneiss antiche,' the ' zona delle 

 pietre verdi,' and the ' terreni cristallini stratificati piu recenti ' of 

 Gastaldi. 4 This classification and the view of the antiquity of the 

 basal gneiss has been accepted by all recent writers on Cottian 

 geology, including, in addition to those already quoted, Baretti, 5 

 Lory, Sterry Hunt, 6 Sacco, 7 and Gianotti 8 ; by all, in fact, since the 

 abandonment of the old view of the Jurassic age of the whole series. 

 This classification, moreover, is in harmony with the almost uni- 

 versal sequence of the pre-Cambrian schists. M. Michel-Levy has 

 referred 9 to the identity in the threefold series in the Central 



1 W. A. B. Coolidge, Alpine Journ. vol. xiv. p. 336. 



2 D. Zaccagna, 'Sulla Geologia delle Alpi occidentali,' Boll. B. Com. geol. 

 Ital. vol. xviii. (1887) pp. 346-417, pis. ix.-xi. 



3 T. G. Bonney, ' Notes on Two Traverses of the Crystalline Bocks of the 

 Alps,' Quart. Journ. Geol. Soc. vol. xlv. (1889) pp. 67-109. 



4 B. Gastaldi, ' Studii geologici sulle Alpi occidentali,' pt. i. Mem. descriz. 

 Carta geol. Italia, vol. i. (1871) pp. 1-48, pis. i.-vi. ; pt. ii. ibid. vol. ii. (1874) 

 pp. 1-61, pi. i. 



5 Baretti, ' Studii geologici sul gruppo del Gran Paradiso,' Atti B. Accad. 

 Lincei, ser.3, Mem. vol. i. pt. i. (1877) pp. 195-313, 7 pis. 



6 T. S. Hunt, ' Gastaldi on Italian Geology and the Crystalline Bocks,' Geol. 

 Mag. 1887, pp. 531-540. 



7 F. Sacco, ' La Geo-Tectonique de la Haute Italie occidentale,' Mem. Soc. 

 Beige Geol. Pal. Hydr. vol. iv. (1890) pp. 3-28, pi. i. 



B G. Gianotti, ' Appunti geologici sulla Valle di Chialamberto (Valle di 

 Lanzo— Alpi Graie),' Boll. Soc. geol. Ital. vol. x. (1891) pp. 149-167, pi. v. 



9 Michel-Levy, 'Note sur la Formation gneissique du Morvan et Comparaison 

 avec quelques autres regions de meme nature,' Bull. Soc. geol. France, ser. 3, 

 vol. vii. (1879) pp. 862-866. 



Q.J. G. S. No. 198. k 



