18 PROCEEDINGS OF THE GEOLOGICAL SOCIETY. [Nov. 20, 



stratified traps. These have generally been regarded as corre- 

 sponding either to the Potsdam Sandstone (Upper Cambrian), or to 

 some of the lowest members of the Lower Silurian ; but Mr. Robert 

 Bell, of the Geological Survey of Canada, has recently put forth the 

 opinion that they are truly of Triassic or Permian age. In the 

 absence of any satisfactory palaeontological evidence, this question 

 cannot be definitely settled ; but the available stratigraphical 

 evidence would rather support the view of Sir William Logan, that 

 the Upper Copper-bearing series is of Lower Silurian age. 



The Lower Copper-bearing series is well exposed on the north 

 shore of Thunder Bay, extending beyond the limits of the bay as far 

 westwards as tbe mouth of the Pigeon river. The series consists 

 in ascending order of: — 1. Green siliceous conglomerates containing 

 pebbles of quartz, jasper, and slate; 2. Grey and black chert -bands, 

 separated from one another by thin courses of dark grey dolomite ; 

 3. Black shales and flags, with associated hornblendic traps ; 4. 

 Grey argillaceous sandstones and shales. jSo organic remains have 

 hitherto been discovered in the Lower Copper-bearing rocks ; and 

 the age of the series is therefore uncertain. It is most probable, 

 however, that tbe group should be referred to the base of the Lower 

 Silurian series. The entire thickness of the Lower Copper-bearing 

 rocks is probably about 1500 feet ; and their general strike is from 

 nearly E. and W. to nearly JST.E. and S.W. The series is traversed 

 by trap-dykes ; and there are also several well-marked interstratified 

 traps. 



The Lower Copper-bearing series acquires a special interest from 

 the fact that it is penetrated by two sets of mineral veins, which 

 promise to become of great importance from the quantity of silver 

 which they contain. The majority of the lodes run along the strike 

 of the beds, having a general E.N.E. and W.S.W. direction ; but 

 there is also a set of transverse lodes, which have a direction more 

 or less nearly north and south. 



Of the north and south lodes, the most important is the now 

 celebrated " Silver-Islet " vein, situated on an exceedingly small 

 rocky islet immediately to the south of Thunder Cape. The vein 

 has a width of from three to four feet, and the vein-stuff consists of 

 quartz impregnated with native silver and galena. Picked specimens 

 of the ore assay from =£1000 to ,£2000 per ton; but this is, of 

 course, exceptional. The mine has only been worked for about two 

 years, but it has hitherto proved extraordinarily productive. 



The most important of the second series of veins, namely those 

 which run along the strike of the stratified rocks and have a general 

 E. and "VV. direction, is the so-called " Shuniah vein." This large 

 vein has been worked at several points along its course, and 

 traverses the Lower Copper-bearing rocks of the north shore of 

 Thunder Bay, running pretty nearly parallel to the shore, and at a 

 distance from it of 1^- to 2 miles. jSTone of the mines on this lode 

 can be said to be as yet out of their infancy ; but the results already 

 obtained are such as to warrant very sanguine expectations. The 

 Shuniah Mine itself is situated about 3^- miles to the N.E. of Prince 



