232 DR. J. W. GREGORY ON THE WALDENSIAN [May 1 894, 



17. The Waldensian Gneisses and their Place in the Cottian 

 Sequence. By J. W. Gregory, D.Sc, F.G.S., of the Briti&h 

 Museum (Nat. Hist.). (Read February 7th, 1894.) 



[Plate XV.] 



Contents. 



Page 



I. Introduction 232 



II. The Cottian Sequence and Previous Literature thereon 236 



III. The Gneisses 239 



(a) The Paradiso Massif. 



(b) The Waldensian Gneisses. 



IV. Conclusions as to the Relations of the Eeds 260 



V. The Contact-Metamorphisin 2K2 



VI. The Origin of the Gneissic Structure 264 



VII. The Age of the Waldensian Gneisses 267 



VIII. Summary of Conclusion^ 274 



Note. — This paper was originally sent in to the Geological Society on October 

 19th. 1892, but owing to the writer's absence from England the reading, and 

 consequently the publication, have been delayed. No reference is therefore 

 made to some recent papers on this and an adjoining part of the Alps, as 

 they do not affect the argument. 



I. Introduction. 



The Cottian Alps consist of three main lines of mountains occu- 

 pying an area roughly triangular in shape, and forming the extreme 

 western segment of the great curve of the Western Alps. They 

 may be divided into three groups : the Northern Cottians, running 

 E.N.E. and W.S.W. from Roche Melon to Mont Thabor; the Western, 

 running from Mont Thabor S.E. to Monte Viso ; and the Eastern, 

 which completes the triangle by continuing the line of the Graians 

 southward from Roche Melon till it joins the Western chain at its 

 southern end. Of these three ridges the Northern and the Western 

 form the main topographic chain, which connects the group of the 

 Graians with the chain of the Maritimes. The arrangement of 

 these two divisions of the Cottians is, to a large extent, independent 

 of their geological structure. Thus Mont Thabor is composed of 

 Carboniferous and Triassic rocks; south-east of this we leave the 

 Triassic limestones at Monte Chuberton and pass to the gabbros 

 and variolitic series of Mont Genevre, which are certainly not earlier 

 than the Upper Mesozoic : to these succeed the calc-schists and 

 mica-schists, and then a vast series of gabbros, serpentines, amphi- 

 bolites (epidiorites, etc.), and glaucophane-schists, which extend 

 from Brie Bouchet to the Viso. Along most of these Western 

 Cottians the direction of the mountains does not agree with the 

 strike of their constituent beds ; branches from the main chain run 

 off along a north-and-south line and show the efforts of the forces 

 of elevation to adapt themselves to the rock-masses which they were 

 upraising. Such, e. <j., is the range that forks from the main chain 



