88 Elements of Mineralogy, 



II. VARIETY. 



Pale, Jlightly Purple, or bluijh Shiftus. 



This ftone is harder than the foregoing, 

 its laminae thicker, and its texture coarfer : it 

 feems to contain a larger proportion of the 

 filiceous and a fmaller of the martial ingre- 

 dient. 



III. VARIETY. 

 Blue Sbi/lus. 



The proportion of the earthy ingredients 

 being the fame as in 'the firft variety, that of 

 the martial ingredient feems to be fmaller. 



Other flones are alfo ufed for covering 

 houfes in various countries, but they are 

 eafily diftinguilhed; as their laminae are much 

 thicker, their furface more uneven, and their 

 texture coarfer. They chiefly belong to the 

 clafs of fand-ftones, or to the calcareous 

 genus, 



IV. VARIETY, 

 Dark Blue Slate> Shift us Script onus. 



It efFervefces more brifkly with acids, and 

 feerns to contain more magnefia, and lefs iron, 



than 



