386 Elements of Mineralogy. 



they are moft commonly parallel to eachother, 



and rife or fall with the mountain. 



The ftrata of which mountains confift, are 

 either homogeneous or heterogeneous. 



Homogenous ftratified mountains confift 

 chiefly of ftones of the argillaceous genus, 

 as fhifti, hornftones, flagftones, or of the fif- 

 file compound fpecies of the filiceous genus, 

 as gneifs, and metallic rock, or of both, the 

 one behind the other. Sometimes of pri- 

 maeval limeftone, that is, limeftone of a gra- 

 nular or fcaly texture, in which no animal 

 veftiges appear. This limeftone repofes on 

 the argillaceous or filiceous ftrata; fometimes 

 the argillaceous are covered with mattes of 

 granite, and fometimes with lava. 



Thefe mountains, as already obferved, are 

 the chief feat of metallic ores, particularly 

 thofe of gneifs, metallic rock, and hornftone. 

 When they are covered with limeftone, the 

 ore is generally between the limeftone and 

 the argillaceous ftones. Thefe ores run in 

 veins and not in ftrata. The calcareous rarely 

 contain any ore, when they do, it is either 

 iron, copper, lead, or Mercury. Petrefac- 



tions 



