Argillaceous Genus. 89 



than the firft variety : its fpecific gravity is 

 2,701. 



SPECIES VII. 



Argillaceous Earth mixed 'with a variable 

 Proportion of Pyrites^ 'with a little Mag- 

 nefia and Calcareous Earth. 



Pyritaceous Shiftus. 



Its colour is grey, brown, blue, or black : 

 it is more or lefs decompofable by expofure to 

 the air, according to the quantity of the py- 

 ritous ingredient and the ftate of the iron in 

 the pyrites : if the iron be in a femiphlogifti- 

 cated ftate it is eafily decompofed, but if the 

 calx of iron be already much dephlogifticated, 

 it will be decompofed but flowly, if at all. 

 Aluminous fchiftus is of this fpecies, but will 

 more properly be mentioned in treating of 

 alum. 



SPECIES VIII. 



Slate, or Pyritaceous Shiftus 9 intimately mixed 

 'with a notable Proportion of Mineral Oil or 

 Bitumen. 



Bituminous Scbiflus. 



It is generally black, of a lamellar texture, 

 of different degrees of hardnefs, but never 



gives 



