ON THE FILLING OF MINERAL VEINS. 31 



Thus in a mine at Schapbach, in the Black Forest, investigated by 

 Sandberger, a vein ran through granite and gneiss. The mica of 

 the granite contained arsenic, copper, cobalt, bismuth, and silver, 

 but no lead. The principal ore in this portion was gray copper. 

 The mica of the gneiss contained lead, copper, cobalt, and bismuth, 

 and the vein held galena, chalcopyrite, and a rare mineral, schap- 

 bachite, containing bismuth and silver, but probably a mixture of 

 several sulphides. No two ores were common to both parts of the 

 vein. Another well-established foreign illustration is at Klausen, 

 in the Austrian Tyrol. Lead, silver, and zinc occurred in the 

 veins where they cut diorite and slates, but copper where mica, 

 schist and felsite formed the walls. In America there are a num- 

 ber of similar cases. At the famous Silver Islet Mine 1 on Lake 

 Superior the vein runs through unaltered flags and shales, and 

 then crosses and faults a large diorite dike. When the diorite 

 forms the walls, the vein carries native silver and sulphides of 

 lead, nickel, zinc, etc., but where the flags form the walls, the 

 vein carries only barren calcite. Along the edges of the estuary 

 Triassic sandstones of the Atlantic border, where they adjoin 

 Archaean gneiss, a number of veins are found carrying lead min- 

 erals, while in the sandstones near the well-known diabase sheets 

 and dikes are others carrying copper ores. It was early remarked 

 by J. D. Whitney that the lead was usually associated with the 

 gneiss, the copper with the diabase. 



1.04.07. From instances like these it is inferred that the ores 

 were derived each from its own walls, and by just such a leaching 

 action by cold surface waters as is outlined above. As opposed 

 to this, it has usually been claimed that each particular wall ex- 

 erted a peculiar selective and precipitating action on the metals 

 found adjacent to it and none on the others ; so that if a solution 

 arose carrying both sets, each came down in its particular surr 

 roundings, while the others escaped. Dr. W. P. Jenney has called 

 the writer's attention to such a case. The Head Centre mine, in 



1 W. M. Courtis, " On Silver Islet," Engineering and Mining Journal, 

 Dec. 21, 1878. M. E., V. 474. 



E. D. Ingall, Geol Survey of Canada, 1887-88, p. 27, H. 



F. A. Lowe, " The Silver Islet Mine," etc., Engineering and Mining 

 Journal, Dec. 16, 1882, p. 321. 



T. MacFarlane, "Silver Islet," M. E., VIII. 226. Canadian Naturalist* 

 IV. 37. 



McDermott, Engineering and Mining Journal, January, 1877. 



