9G M. Foiirnet*s llesearches on the Geology of the Alps, 



erases; then come the conglomerates of Valorsine, with 

 their micaceous paste and black slates. At the cascade of 

 Pissevache, we again find petrosiliceous veins ; at the cas- 

 cades of Mieville, we perceive felspar and micaceous rocks. 

 Finally, from Mieville to Evionnaz, the geological chart of 

 France, indicates that the valley intersects the axis of the 

 chain of Brevent. All this system is parallel to the Western 

 Alps. 



" If we take account," says the author, " of the result of 

 metamorphic actions, we may group these products (these 

 stratified and altered formations, in the following manner : — ■ 



" 1*^, The baking of schistose clay into argillaceous or 

 clay slates. 



" 2d, The conversion of ordinary slates into hard unc- 

 tuous slates, more or less modified in their colours. 



" 3^, Complete hardening or semi-fusion, which has caused 

 the slates to pass into a petrosiliceous state. 



" 4M, Crystallisation into chlorite of the slaty fragments 

 embedded in the veins of quartz. 



" bth. Transformation of the clay slates into green slates, 

 more or less felspathic, and very variable in the grain. 



" 6M, Change of the same rocks into felspathic micaceous 

 slates, or into gneiss more or less porphyritic, in conse- 

 quence of an imbibition and crystallisation of mica and fel- 

 spar. 



" 1th, Lastly, crystallisation of black limestones into white 

 limestones, saccharoidal, or saline, with or without idocrase." 



He then proceeds to examine the different changes which 

 the rocks have undergone. It then becomes indispensable 

 to inquire into the nature of the rocks. Now, two kinds here 

 present themselves to him as fundamental, namely, the lime- 

 stone and clay state. M. Fournet first takes up the latter, 

 the metamorphism of which appears to be more general, 

 more complicated, than that of the limestone, on account of 

 its variety of composition, and its exfoliability, — a circum- 

 stance which multiplies the points of contact. What is the 

 composition of clay-slate \ What is its constitution I Is it 

 itself a metamorphic rock % These are some of the problems 

 discussed. 



