THE MINING AND QUARRY INDUSTRY I912 105 



The occurrence of vein quartz of the same character as that asso- 

 ciated with the granites and pegmatites of the surrounding region 

 is the only indication, so far as observed, of the possible influence 

 of igneous agencies in the introduction of the ores. The whole area 

 of gneisses and schists bordering the limestone belt shows frequent 

 intrusions of granite and pegmatite, offshoots apparently of some 

 neighboring or underlying granite body. With the feldspathic peg- 

 matites are found quartz veins in such relation as to indicate a 

 common source. No close correlation in time can be made between 

 the period of ore foundation and the invasion of the granite, but 

 the latter can be confidently assigned to the later part of the Pre- 

 cambric. If the view as to the deposition of the sulphides in depth, 

 rather than near the surface, is correct, then they also probably 

 belong to the Precambric, as erosion has not been very marked 

 upon the limestones since that period. The fact that the ores show 

 effects of regional compression, though not to the same extent as 

 their wall rocks, is a further argument in favor of a Precambric 

 age, as there has been little disturbance of that nature in subse- 

 quent time. The intrusion of the granite, if not actually contribut- 

 ing to the body of underground waters, would have facilitated their 

 circulation and added to their chemical efficiency. 



