Mt>DE V. LIME- SLATE. 



and in like manner quartzose micaceous schistus 

 is seldom found which does not 4 yield some bub- 

 bles in acids, and which, reduced to powder, 

 does not lose some of its weight in distilled 

 vinegar. 



" These micaceous calcareous schisti are not 

 common. Those authors who have written sys- 

 tems of mineralogy have not known them, or at 

 least have neither classed them, nor given them 

 names in their works. I have described, in the 

 second volume of these travels, 996, those 

 which I discovered in the valley of Aosta in 

 1778; but in them the free calcareous part is 

 never predominant, it forms at most but the 

 fourth part of the rock. Those of Mont Cenis 

 differ also in the colour of the mica, which is of 

 an iron grey, or verging to blue, while that of 

 the valley of Aosta is white or yellowish. 



"The first rocks of this kind, which are met 

 with above Lans-le-Bourg, have very thin and 

 very fragile plates: they rise to the E. S.E., un- 

 der an angle of twenty degrees; higher, after 

 having crossed a little bridge, the same schisti 

 are found in an opposite position, or rising to 

 the west. But this position is accidental ; it 

 may be said that in general they rise to the 

 E. S,E,, following the slope of the mountain."* 



* Sauss. J234. 



