114 



KEMP'S ORE DEPOSITS. 







in central North Carolina, in schistose 

 rocks, which have been referred to the 

 Huronian. 



2.02.31. Lenses of specular hem- 

 atite of very excellent quality are found 

 also in metamorphic rocks, north of Fort 

 Laramie, Wyoming, which may prove 

 productive in time. But little is as yet 

 known about them. 



2.02.32. Example 11. Pilot Knob, 

 Mo. Two beds of hard specular hem- 

 atite separated by a thin seam of so- 

 called slate (probably volcanic tuff), and 

 interstratified with breccias and sheets 

 of porphyry. Along the eastern limit 

 of the Ozark uplift of Missouri and 

 Arkansas a series of knobs of granite 

 and porphyritic rocks project through 

 the Cambrian limestones and sand- 

 stones. They are older than the lime- 

 stones, and clearly were not intruded 

 through them. The limestones and 

 sandstones lie up against the porphyry 

 and in the valleys between. The un- 

 derlying porphyry has been found in 

 the valley near Pilot Knob, after pene- 

 trating four hundred feet of sediment- 

 ary rocks. The porphyry and ores 

 have often been called Huronian, but 

 in view of the recent reorganization of 

 the Huronian (see Example 9), this is 

 not done, nor ever has been, on any ac- 

 curate grounds. Pilot Knob is formed 

 by one of these eruptive knobs. It con- 

 sists of sheets of porphyries that are 

 capped by porphyry breccia, the two 

 ore beds, and the intervening tuff. The 

 beds strike and dip 13 S. S. ^^ r . The 

 hill is over 600 feet high. The lower 

 bed has furnished most of the ore, run- 

 ning from 25 to 40 feet thick, and af- 

 fording a dense bluish, specular hema- 

 tite of from 50 to 60# Fe, siliceous, and 

 very low in phosphorus. The upper bed 



