302 D. H. Browne — Phosphorus in Iron Mtn., Mich. 



noticed in the direction from west to east. Sometimes a de- 

 crease is manifest, and sometimes an increase, these being both 

 easily accountable for. The analyses taken from west to east 

 are not nearly so regular and uniform as those taken from foot 

 to hanging wall ; nor is this to be wondered at ; for since the 

 layers of ore present smooth surfaces in the direction of the 

 walls, analysis taken along a series of sets on the footwall will 

 represent roughly analyses of at most a very few layers of ore. 

 In driving a drift, or stoping a room, or sinking a winze, on 

 the other hand, where analyses are made, averages are taken of 

 a large number of separate deposits, and as these deposits are 

 much flexed and broken, the analyses show little correspondence. 

 In the breast of a drift 8 feet wide, supposing each layer of ore 

 has a thickness of half an inch, there will present themselves 

 for analysis the edges of no less than 192 layers ; and in con- 

 sequence more confusion is liable, and does occur, in analyses 

 taken east and west than in those taken north and south. 



Having obtained thus a general idea of how the lines of 

 phosphorus tend in two directions ; the next question naturally 

 is, what would be the lines of equal phosphorus content in any T 

 individual layer of ore. These, for want of a better term I 

 have herein been obliged to term " isochemic lines." It is 

 evident that analyses of ore in the breast of a drift, or in the 

 bottom of a winze, would not give any clue to the isochemic 

 lines in a particular stratum of ore, but would show the average 

 of several hundred separate strata. It is also evident that no 

 analysis would accurately represent the composition of a par- 

 ticular layer, unless this layer, in no case over half an inch, 

 and rarely over one-quarter inch in thickness, could be followed 

 by chemical analysis along drifts, and up slopes, and down 

 winzes and shafts, for a distance in some way proportionate to 

 the extent covered by the deposit of which it forms an infin- 

 itesimal thickness. This would be, and for me was, practically 

 impossible. For analyses to be of commercial value, must 

 show, not the amount of constituents in any particular stratum 

 of ore, but the average of that amount of ore which a gang of 

 men, working under contract, can take out of a given room, 

 before other analyses be made. For this reason I have been 

 obliged to confine myself to analyses which represent averages 

 of a large number of layers ; and from these analyses I have 

 endeavored to outline the probable distribution of phosphorus 

 in the separate strata. It is plain that if any single layer of 

 ore shall have its percentage of phosphorus in some way modi- 

 fied by its method of deposit, every other layer subjected to 

 the same conditions will be in similar manner modified, and 

 consequently, analyses representing average of a large number 

 of strata will show the characteristics common to each indi- 

 vidual stratum. 



