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071 the Lake Superior Land District. 237 



The silver in this vein is found in thin leaves, between the 

 laminae or joints of the crystallized spar, indicating that it was 

 deposited subsequent to the filling of the vein, 



At the Minnesota mine it is not unusual to iind spongiform 

 copper adhering to the walls, which would seem to indicate that 

 copper was the first substance deposited in the fissure. Again 

 we find it deposited in thin plates between the joints of the crys- 

 tallized quartz, which would indicate that the latter was deposited 

 subsequent to the former. We have before us a specimen from 

 this mine, consisting of native copper, native silver, crystallized 

 quartz, and carbonate of lime, (calc-spar.) The copper and sil- 

 ver are distinct, and appear to be chemically pure. The form of 

 the crystals of quartz is impressed on the stiver and copper, and 

 m the body of the crystals there is no trace of a metallic sub- 

 stance. The calc-spar, however, conforms to the silver and cop- 

 per, both of these metals being disseminated through it. The 

 silver occurs in imperfect octohedrons of the size of a pea. 



This arrangement would seem to indicate the following order 

 3n the deposition of the materials: 1. Quartz; 2. Copper and 

 silver; 3. Calc-spar. 



At the Cliff and North American mines perfect crystalsof cop- 

 per occur only in the cavities of the matrix; when in contact 

 with quartz, it takes the form of this substance. 



The inference from these facts is, that some of the earthy 

 niaterials constituting the veinstone were deposited prior to the 



copper and silver, while others were subsequent in their de- 

 position. 



The silver is generally found to occupy a certain position in 

 the lode. Thus, at the Copper Falls mine, it is most abundant 

 near the junction of the trap and conglomerate on the north; at 

 the Cliff mine, near the junction of the crystalline greenstone 

 ^»id granular trap. Although silver is intimately associated with 

 copper, yet it does not occur in sufficient quantity to justify the 

 expense of separating the two metals. The lodes are frequently 

 brecciated, the angular fragments evidently having been derived 

 from the adjacent walls — and are most abundant above the points 

 where the fissure is nearly closed."— pp. 172-174 



The authors adopt the electro-chemical theory in explaining 

 the origin of the veins. The fact that the copper is found invest- 

 ing minerals, copying every wave and stria, and even incrusting 

 zeolitic crystallizations which could not have stood the heat of 

 lusion, favors this view of their origin. 



This article has already exceeded our estimated limits and we 

 omit therefore other citations marked off, and close with a few par- 

 agraphs on the Clif Mine, pp. 127-130. 



