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No. 6.] DOUGLAS — LAKE SUPERIOR COPPER MINES. 323 



with small amjgdules, is of a deeper red and breaks with a more 

 uneven fracture. The minerals which fill the amygdules in the 

 barren bed, viz., quartz, calcspar, laumonite, prehnite, not only 

 fill the amygdules here, but likewise form irregular veinlets rich 

 in copper ; and the chlorite constituents of the rock prevail so 

 largely in parts as to give it a deep green shade. Pellicles of 

 native copper enveloped in chlorite often occupy the centre of the 

 arbygdules. We see here the tendency of the copper to aggre- 

 gate with the quartz, and the same zeolitic minerals as compose 

 the fissure veins of the Easle River and the bedded veins of 

 the Ontonagon districts ; and, therefore, if we attribute the for- 

 mation of the one to aqueous agencies, are led to ask whe-ther 

 the same agencies have not had more to do with the formation 

 of the beds and their mineral contents than has generally been 

 attributed to them. 



Sheets of native copper occur between the joints of the trap in 

 the copper bed, and formed evidently through infiltration, arc 

 found also between the trap blocks beyond the walls of the bed. 

 An indication of subsequent aqueous action is seen in the streaks 

 of clay which smear to a great depth the faces of the trap blocks- 

 A single cross course, carryinp; quartz, but no copper, is said to 

 have been met with. The width of the bed of copper bearing 

 ground is supposed to be about 70 feet ; not that in a'^ ^ x)lace 

 70 feet of productive rock has been found, but when coppci '^as 

 been lost on one wall, as much as 70 feet have been driven 

 through what is supposed to be the same bed, and copper found 

 in what has been taken for the other wall. More than once, 

 cross cuttings for many fathoms have thus resuscitated parts of 

 the mine where it was feared the copper had given out altogether. 

 The suddenness with which the rock will change and lose its 

 metalliferous character is very remarkable, and affects, naturally, 

 the productiveness of the mine from year to year. 



Copper-bearing beds alternate, however, with barren trap for 

 a distance of 500 feet, as determined by a cross cut eastward 

 from the 70 fathoms level of the neighbouring Pewabic Mine. 

 In the report of the agent of that mine, in 1863, he anticipates 

 that the following copper beds would be reached at the distances 

 indicated. The results justified his predictions. From the 

 Pewabic lode, the distances of the adjacent strata were: — ■ 



