82 BOCK-METAMORPHISM. 



taining carbacid solutions, ever present in deeply-seated 

 rocks, and that, under the influences stated, the " granitic 

 veins " and the bedded " pyroxenytes " have gradually 

 undergone changes, which eventually converted them re- 

 spectively into " calcareous veins " and beds of " crystalline 

 limestone." 



If any extensive beds of really pure limestone, resembling 

 carrarite, are included in the great Archsean class of rocks, 

 we should, rather than ascribe them to simple mineralization 

 as we do the marble named, prefer the suggestion that they 

 have been deprived of mineral silicates through the latter having 

 been washed out by dissolving waters. 



