APPENDIX A. 



159 



In Union River, a short distance west of Little Iron River, at the 

 foot of the Porcupine Mountains, brown sand rock and conglom- 

 erate ledges of great thickness are uncovered in the bed of the 

 creek, dipping at an angle of from 20° to 30° in a northeast direc- 

 tion. 



The beds can be directly followed in descending series by going 

 up stream toward Union mine, where they are seen in conformable 

 superposition on the amygdaloid trap belt in which Union mine is 

 opened. Under the amygdaloid belt other conglomerates and 

 sand-rock strata are found, which can not be distinguished in litho- 

 logical characters from the upper beds. A natural exposure of the 

 two sand-rock belts with the amygdaloid rock between is seen in a 

 ravine close to the side of the road leading from Union mine to the 

 Nonesuch mine. The foot-wall sand rock of the Nonesuch mine 

 seems to be the analogue to the hanging wall of the Union mine. 

 On the west side of the Porcupine Mountains, the shore belt has 

 the same geological structure as the Iron River district, and in all 

 probability the silver-bearing rock seams can be found there also. 



The silver is extracted from the rock by stamping all the rock 

 as it comes from the ledge, without selection, and subjecting the 

 stamped rock to the amalgamation process. The results of the ex- 

 periments were quite variable, yielding, per ton of rock, from fifteen 

 to fifty dollars' worth of metallic silver. The process of amalgama- 

 tion was very imperfectly carried out, leaving in the sediments which 

 settled from the wash-water a considerable proportion of amalgam 

 globules. I am fully convinced, therefore, that, by proper manage- 

 ment of the process, the average quantity of silver per ton would 

 not be less than thirty dollars. The silver seems not to be confined 

 to certain localities, but to have a wide horizontal distribution in this 

 rock seam ; still it would be unreasonable to expect that in every 

 locality where these rock beds are found, they should contain silver 

 in quantities to make mining remunerative. 



REPORT ON THE SLATE QUARRIES OF HURON BAY. 



By special order of the Board of Geological Survey, I left on 

 August 23d, 1875, for Lake Superior district to examine the slate 

 quarries on Huron Bay, with a view to reporting on the conditions 



