D. II Browne — Phosphorxis in Iron Min., Mich. 309 



The subsequent action of water upon the upturned edges of 

 the eroded deposit would of course in large measure modify 

 the chemical peculiarities of the ore. This is proved by the 

 fact that the greatest regularity of isochemic lines is manifest 

 where the ore is shielded from surface water by the overhang 

 of the western jasper ; and by the fact that at the eastern end 

 of the mine where the ore has been exposed under the drift, 

 this regularity is not so manifest. That the original direction 

 of deposition was from west to east is shown by the occurrence 

 underground of strong streams of water flowing from the rock 

 at the western extremity of the ore deposit. 



The theory of aqueous deposit will explain, as will no other, 

 the marked regularity of isochemic lines and their peculiar 

 curves, the regular decrease of phosphorus from hanging wall to 

 foot, the alternation of carbonate of lime and oxide of iron, the 

 ripple-marked hanging wall, the uniform lamination of the ore 

 and the hydrated muddy deposit next the footwall. It also 

 suggests explanation of the general features of the Menominee 

 Range, and the gradual change from high phosphorus and low 

 iron ores resembling altered bog ores at its western extremity, 

 through regular deposits of high iron and lower phosphorus, to 

 the immense washes and surface deposits of exceedingly low 

 phosphorus ore which mark its eastern termination. 



The conclusions herein given are not intended as general and 

 applicable to all cases. They are intended simply as an expla- 

 nation of certain chemical phenomena noticed in a careful 

 study of the Ludington mine. Whether such tendencies would 

 be found in other mines I am not prepared to say ; but the fact 

 that irregularity of chemical composition has been often noticed 

 does not preclude the possibility of a method or law of irregu- 

 larity existing. I incline to think that careful and systematic 

 chemical research applied to the soft ore deposits of the upper 

 Peninsula would bring to light many interesting facts with 

 regard to their manner of deposit, and would lead to a more 

 thorough understanding of one of the most practical and 

 interesting problems of economic geology. 



EXPLANATION" OP FIGURES. PLATES VIII TO XIII. 



Fig. 1. Horizontal cross section of small vein. 



Fig. la. Horizontal cross section of vein showing curvature. 



Fig. 2. Vertical cross section of same, showing curvature of hanging wall. 



Fig. 3. Vertical longitudinal section showing form of hollows in which ore is 

 deposited. This section is ideal, but corresponds with several known sections. 



Figs. 4-16. Horizontal cross sections of various rooms in the Ludington mine. 

 In all figures the hanging wall is toward the top of the plate, and the west end 

 toward the left, as shown in fig. 4. Figures indicate percentages of phosphorus 

 in the ore removed. 



Fig. 18. Vertical longitudinal section of No. 5 room, A shaft, 6 level, in the 

 plane of the winzes, showing curvature of isochemic lines. The figures show 

 percentage of phosphorus in the ore at the poiuts indicated. 



