Vol. 6t > .~] southern origin of THE SAVOY AND SWISS ALPS. 307 



supposed the Schistes lustres to exhibit a progressive meta- 

 morphism, but in the district under discussion the name covered 

 two groups of rocks — one, mica-schists, sometimes containing well- 

 developed garnets and staurolites, passing into marbles, etc. ; 

 the other, merely schistose slaty rocks, in which metamorphism 

 was but slight. Sometimes the latter were of Palaeozoic age, but 

 in this part of the Lepontine Alps they were shown by fossils 

 to be Jurassic. Below them, often, though not always, was the 

 friable limestone called 'rauchwacke', very different from the crys- 

 talline limestones of the schists ; and in this rauchwacke, not seldom, 

 were fragments of rocks identical with those in the group of 

 crystalline schists. The only appearance of a passage from the one 

 group to the other was where (in the absence of the rauchwacke) 

 excessive crushing along the line of junction deprived the two rocks 

 of their normal characters. This was not a question of opinion but 

 of fact, and he could demonstrate it to any competent geologist who 

 liked to examine his collection of rocks and of sections for the 

 microscope, which was now in the Sedgwick Museum at Cambridge. 



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