130 KEMP'S ORE DEPOSITS. 



to demonstrate. The limonite may Lave resulted from the oxida- 

 tion of lenses of pyrite. 4. As replaced limestone beds, or as sider- 

 ite beds subsequently metamorphosed. Such deposits may pass 

 through a limonite stage. The general process is outlined under 

 Example 9c, as developed by Irving and Van Hise in the Gogebic 

 district. The lenticular deposits of siderite at the Burden mines 

 (Example 4) are very suggestive, and some such original mass 

 might in instances be metamorphosed to magnetite. 5. As sub- 

 marine chemical precipitates. This is outlined under Example 9c?, 

 as applied by the- Winchells in Minnesota. 6. As beach sands. 

 The lenses are regarded as having been formed as outlined under 

 Example 15. The same heavy minerals sometimes occur with 

 magnetite lenses as are found on beaches. (See B. J. Harrington, 

 Can. Geol. Survey, 1873, 193 ; A. A. Julien, Phil. Acad. Sci.y. 

 1882, 335.) 7. As river bars. This regards the lenses as due to 

 the concentration of magnetite sands in rivers or flowing currents. 

 Hence the overlapping lenses, the arrangement in ranges or on lines 

 of drainage, and the occasional swirling curves found on the feather- 

 ing edges of lenses, as in the Dickerson mine, Ferromont, N. J. 

 (See H. S. Munroe, School of Mines Quarterly, Vol. III., p. 43 an 

 important paper.) It is also reasonable to suppose that lakes or 

 still bodies of water may have occurred along such rivers, and have 

 occasioned the accumulation. (As segregated veins, see Addenda.) 



Several other hypotheses with small claims to credibility could 

 be cited. They are outlined at length in J3ull. VI., Minn. Geol. 

 Survey, p. 224, but in this place there has been no desire to take up 

 any but those deserving serious attention. It may be said that while 

 one or the other of the above seven hypotheses may in instances be 

 applied with reason, yet most candid observers with widened ex- 

 perience have grown less positive in asserting them as axiomatic. 



2.03.15. Of importance in connection with iron ore deposits 

 are the recent studies of the distribution of phosphorus along 

 certain lines in the beds, by a knowledge of which it is possible to 

 keep more valuable Bessemer ore distinct from less valuable. 

 Such lines have been found in Michigan, and have been called 

 by Mr. Browne " isochemic lines." Though less marked at the 

 Burden mines (Example 3), the phosphorus was characteristic of 

 certain varieties of the ore. Much work has also been done on 

 the same question at Iron Mountain, Mo. 1 



1 D. H. Browne, " On the Distribution of Phosphorus at the Luddicg- 



