Vol. 50.] GNEISSES IN THE COTTIAN SEQUENCE. 237 



Miocene. 



Eoceiie. 



Cretaceous. 



Jurassic. 



Triassic. Grey, schistose, compact, and brecciated limestones, talc-schists with 



serpentines, etc. 

 Permian. 

 Carboniferous. 



Pre-Pakeozoic. Zone of mica- 1. Calc-schists, mica-schists, quartzites, 

 schists, etc. with saccharoidal limestones, tabular 



gneiss with syenites and granites. 



2. Do. with serpentinous rocks, gabbros, 



diabase, and amphibolic, epidotic, 

 and chloritic rocks. 



3. Do. with massive diabase and por- 



phyry. 

 Zone of Central Gneiss, augengneiss with white granite, 

 Gneiss. talcose and micaceous granites (pro- 



togine of Mont Blanc). 



With the Cainozoic and Mesozoic beds we have little to do ; the 

 important points are : — (1) that Zaccagna agrees with Gastaldi and 

 some earlier writers that the whole of the true schists and the more 

 normal sediments associated with them must be assigned to the pre- 

 Palaeozoic ; (2) that he maintains that a definite sequence in them 

 can always be established, and that the beds of ' central gneiss,' 

 which Gastaldi and Baretti regarded as accidentally distributed 

 through the schists, occupy a constant position at the base of the 

 series. In his map he represents the ' central gneiss ' as forming a 

 continuous band from Bussoleno to Venasca, and in his section 

 across the Southern Cottians shows it as occupying the axis of a great 

 anticlinal. In his summary of conclusions he is very emphatic that 

 " the central gneisses are not a mere lithological accident in the 

 mass of mica-schists and other crystalline rocks, .... but they hold 

 a constant place in the series and form the base and the nucleus of 

 the various ellipsoids of elevation." Further, he maintains (pp. 415, 

 416) that "there does not exist a gradual passage between the crys- 

 talline rocks of the Alps and those of the fossiliferous series, as we 

 ought to admit if we adopt the opinion of Lory, according to whom 

 the Archaean calc-schists of the Cottian Alps and of the valley of the 

 Arc represent a great part of the Triassic series." 



In complete accord with the views of Zaccagna upon these main 

 points are those of Prof. Bonney, who in 1889 ' published his ' Notes 

 on Two Traverses of the Crystalline Hocks of the Alps.' Bonney's 

 two most important conclusions were the fundamental unity of 

 the sequence of gneisses and schists in the Eastern and the Western 

 Alps and their Archaean age. He crossed the Cottians to the north 

 of Zaccagna's main section and concludes " that, broadly speaking, a 

 stratigraphical succession can be detected in the gneisses and schists 

 of the Alps, and that these rocks are of Archaean age." He strongly 

 opposed Lory's view of the Triassic age of the ' schistes lustre's,' or 

 calc-schists of Cesana, and attributed them to his Upper Archaean 



1 Quart. Journ. Geol. Soc. vol. xlv. pp. 67-109. 



