308 D. H. Browne — Phosphorus in Iron Jftn., Mich. 



end of the lake, and to deposit them in shallow water, along 

 banks of previously precipitated silica, and in places where 

 evaporation was most rapid. By reference to fig. 23, it will 

 be seen that those parts of the deposit where the current must 

 have been deep and unbroken are low in percentage of phos- 

 phorus, while the high phosphorus as a rule occurs where the 

 deposit is shallow or the ore pinched out by rock. After the 

 deposition was complete, further action of the water would 

 stir up the upper layers of ore, and mix them with suspended 

 sand or clay, while the iron and phosphorus were carried far- 

 ther along to be deposited in other depressions to the northeast. 

 As jasper occurs as vein matter, and in laminse cleaving in 

 the same line as the ore, it would seem, either that the jasper 

 had been produced by precipitation with the iron, or that 

 subsequent action of water has eroded the beds of iron thus 

 formed and substituted silica for the iron removed. 



A study of the vein map of the 6th level at the Ludington 

 mine, on which level almost the entire deposit was replaced by 

 jasper, and in consequence the formation of the jasper was 

 most evident, seems to show that the jasper is a later formation 

 than the ore. It will be seen by reference to fig. 17 that the 

 jasper deposit widens toward the footwall. A large horse of 

 jasper occurring in the ore at the eastern end of the vein shows 

 this very plainly. This would seem to indicate that at a time 

 when the ore deposit was about half its present width an inflow 

 of silica-bearing water eroded the ore deposit and deposited 

 silica in piace of the iron abstracted. The greater width of the 

 jasper at the footwall also suggests an erosion of the original 

 ore bed and a subsequent deposition of silica. Had the silica 

 been the primary deposit the ore would be widest at the foot- 

 wall instead of at the hanging. 



The explanation, however, of the deposits of silica bedded 

 in the same plane with the ore, in some cases stopping sharply 

 against ore, in others merging gradually into it, is at present a 

 very difficult problem. The explanation suggested by Prof. 

 Tan Hise seems to me more satisfactory than any other, with 

 the provision, however, that subsequent erosion must be taken 

 into consideration. Whatever explanation of the horses of 

 jasper be adopted, it is evident that both ore and jasper after 

 formation were covered by the slates and other superincum- 

 bent strata, and in some local upheaval tilted up from the 

 north and brought into their present position. 



The erosion of the Glacial period removing several hundred 

 feet of the outcropping strata has cut away a large part of the 

 original deposits, and from the ore thus eroded have been 

 formed the surface deposits or washes of ore found at Keel 

 Ridge, Quinnesse and Norway mines. 



