Chap. 46.] Alluvial Mountains. 315 



animals, for no organic traces are found in them. 

 Some of thofe, which confift of argillaceous ftones, and 

 fome of the filiceous, contain alfo no organic remains. 

 Thefe often confift of parallel ftrata of unequal thick- 

 nefs, and the lower are harder and lefs thick than the 

 upper, and therefore feem to have been formed earlier 

 than the upper. 



Alluvial mountains are evidently of poflerior for- 

 mation, as they contain petrifactions and other vef- 

 tiges of organic fubftances, and thefe are always ftra- 

 tified. 



Mountains, as to ftruclure are entire, ftratifred, and 

 confufed. Entire mountains are formed of huge 

 mafies of (lone, without any regular fifiures, and are 

 mollly homogeneous. They confift chiefly of granite, 

 fometimes gneifs*, fchiftus, flag-ftone, fand ftone, lime- 

 ftone, gypfum, porphyry or trapp. Some in Sweden 

 and Norway confift of iron ore. 



The ftratified mountains are thofe whofe mafs is 

 regularly divided by joints or fifTures; thefe are called 

 horizontal, rifing, or dipping. Homogenous ftratified 

 mountains confift chiefly of ftones of the argillaceous 

 genus, or of the firTile compound Ipecres of the fili- 

 ceous genus, as metallic rock ;" fometimes of lime- 

 ftone of a granular or fcaly texture, in which no animal 

 veftiges appear. This lime-ftone repofes on the 

 argillaceous or filiceous ftrata: fometimes the argil- 

 laceous are covered with mafles of granite, fometimes 

 of lava. Thefe mountains, particularly thofe ofgneifs, 

 metallic rock, and horn-ftone, are the chief feat of 

 metallic ores. When covered with lime-ftone, the 

 ore is generally between the lime-ftone and the argil- 

 laceous ftones. Thefe ores run in veins, not in ftrata. 



* A rock confiding of mica, lapU ollaris, and quartz. 



Petrifactions 



