468 DOMAIN V. CALCAREOUS. 



Saussure observed many mountains in the 

 Alps chiefly composed of what he calls mica- 

 ceous limestone, often alternating with mica 

 slate. The following observations occur in his 

 description of Mont Cenis, celebrated for the 

 passage into Italy. 



" Soon after is observed the micaceous schis- 

 tu>s, which really forms the body of the moun- 

 tain, but which is also found in some places 

 covered with tufas. These schisti contain cal- 

 careous earth, with a granular and brilliant 

 aspect, such as it assumes in primitive moun- 

 tains: it is even in such quantity that these 

 schisti strongly effervesce with the nitrous acid; 

 and become friable, after having remained some 

 time in it. 



" It will be seen hereafter that calcareous earth 

 and mica are found at Mont Cenis, mingled in 

 all proportions ; from limestones nearly pure, in 

 which only a few plates of mica are observable, 

 to the micaceous rock, which contains little or 

 no free 'calcareous earth, and in which quartz 

 supplies the place occupied by the limestone in 

 the former. There is nevertheless this remark- 

 able circumstance in the schisti of Mont Cenis, 

 that those which are calcareous are seldom found 

 free from quartz, as is proved by the sparks that 

 may be almost always obtained from it by steel $ 



