54 



PROTOZOIC ROCKS 



through ferruginous earthy matter composed chiefly of the brown oxide of 

 iron.* 



It was first discovered by a Mr. Sterling, in March, 1843, on the north slope of 

 a hill, the foot of which is watered by Copper Creek, a small tributary which runs 

 west into the Mississippi, though the locality is only four and a half miles from the 

 Kickapoo. It Avas subsequently explored to some extent by the same individual, 

 and proved to be a bed from twelve to fifteen feet wide and five to seven deep, 

 spreading out, as it descended the slope, to thirty feet wide, and conformable to the 

 outline of the hill. On tracing it to the south, it was followed to near the brow of 

 the hill, where it pitches to the southeast parallel with a wall of magnesian lime- 

 stone, and almost perpendicularly. The wall of magnesian limestone is quite solid, 

 and without apparent stratification. A shaft of fifty feet was first sunk from the 

 surface ; then a drift of ninety feet was run on the west side of the perpendicular 

 wall of rock ; and afterwards another shaft of twelve feet at the end of the drift. 

 To the north a gallery was run forty feet, and then six feet sunk perpendicularly. 

 The copper ore extended both horizontally and vertically as far as these excavations 

 were carried. Below the bed of copper ore, on the slope of the hill, was a tough, 

 greenish-gray earth, fifteen inches thick, and about the same width as the bed of 

 ore. The whole rested on broken masses of magnesian limestone with green seams 

 running through them. 



The position of the copper ore, green earth, and fragmentary rock, indicates that 

 it was once enclosed in a fissure of magnesian limestone. By decaying and denu- 

 ding influences the walls seem to have parted, so that the northwest side fell down 

 the slope towards Copper Creek, along with the ore and vein-stuff, which seem 

 subsequently to have been partially removed and scattered down the declivity by 

 the agency of rains and floods. Small pieces of rock of the appearance of trap were 

 found mixed with the ore, but none was discovered in place anywhere in this vicinity. 



The mine lies well for drainage, and the ore is of a kind easily reduced in the 

 furnace, and yields so good a percentage of copper (about twenty per cent.) that it 

 would be well worth the expense to prove this mine further than has yet been 

 done. At a small cost, the value of this discovery could be determined by ascer- 

 taining to what extent the ore is likely to traverse the magnesian limestone before 

 entering the sandstone ; in which latter formation, the vein would probably dwindle 

 or entirely disappear. 



* The analysis of this copper ore, in the humid way, gave, from a gramme : — 



Water, 11-2 



Carbonic acid, . . . . . . 05-0 



Insoluble silicates, with a trace of oxide of iron, 08 - 3 



Protoxide of copper, ..... 25 - 0 = 19-87 per cent, of Metallic Copper. 



Peroxide of iron, . . . . . . 48-7 



Protoxide of manganese, .... 00 - 2 



Alumina, ....... 00-6 



Carbonate of lime, ..... 00-8 



Loss, 00-2 



100-0 



