SOUDAN FORMATION. 



185 



broken. The following table, made by Mr. R. B. Green, in 1898, at the 

 Minnesota Iron Companj^ laboratory at Two Harbors, Minn., shows the 

 coarseness of the Chandler and Pioneer ores of Ely. Ores from Soudan 

 are, perhaps, even coarser. 



Percentage of ore from Chandler and Pioneer mines, Ely, Minn., that passes through 

 screens of specified mesh per inch. 



[Determined in natural state after taking from ears and drying.] 



Chandler ore (28 cargoes) 



Long Lake ore, Chandler mine (13 cargoes) 



Pioneer ore (23 cargoes) 



Pilot ore, Chandler mine (2 cargoes) 



82.05 

 76.99 

 77.50 

 65.65 



9.14 

 10.94 

 11.00 

 13.93 



2.94 

 3.98 

 4.42 

 8.97 



MICROSCOPIC CHARACTERS OF THE IRON-BEARING FORMATION PROPER. 



The iron-bearing formation proper consists of the various colored 

 cherts, griinerite-magnetite-schists, hematite, magnetite, and limonite. With 

 the iron-bearing formation proper, but in quantity very subordinate to the 

 cherts, jaspers, and iron oxide, there occur some greenish to gray slates, and 

 also graphitic slates. Upon close examination under the inicrosco])e these 

 do not show evidence of their clastic character. False bedding would per- 

 haps indicate their clastic origin, but no other evidence of this has been 

 found other than their similarity to the slates above mentioned, which grade 

 into the recognized elastics. 



The white chert, in combination with various minerals which color it, 

 forms the bases of the colored varieties of cherts already enumerated on 

 page 181. When pure the white chert consists of quartz varying in size 

 of grain from that which is minutely crystalline to that which is somewhat 

 more coarsely crystalline. The grains are polygonal and generally more 

 or less roundish. In one case, in a relatively coarse-grained chert, three 

 quartz grains were observed which showed a roundish core outlined by 

 a film of iron oxide, and beyond the iron oxide a zone of clear quartz. 

 This secondary enlargement might possibly be taken as evidence of the 

 clastic origin of the grains, but this structure is not sufficient evidence 

 of such origin, and even if it were considered sufficient proof for the 

 grains it would not be sufficient evidence to prove this origin for the 



