The Iron Bearing Rocks of Minnesota — Winchell. 277 



the freshest pieces but scattered through these are numerous 

 grains of a partially decomposed mineral, which is doubtless oli- 

 vine. Probably it is the decomposition of this mineral which 

 forms the metallic portion of the more altered slides. One inter- 

 esting feature of the fresher porphyrite is the fact that the inter- 

 stitial augite which acts as the matrix for the feldspar individuals, 

 extinguishes simultaneously over quite large areas, a fact which 

 has been observed in both granites and gabb os as well as in the 

 fresher portions in the so called mottled melaphyr of Pumpelly, 

 here in the northwest. 

 April 2, 1889. 



[Paper FF.^ 



THE IROI^ BEARING ROCKS OF MIIfNESOTA. — H. V. WmchelL 



[abstract.] 



After speaking of the mining industries of northeastern 

 Minnesota and pointing out on a chart some of the geographic 

 and geologic features of our state Mr. Winchell continued : 



The oldest formation in which we find iron bearing strata is 

 the crystalline schist series, called the Vermilion series by the 

 Minnesota geologists. 



This formation consists of mica and hornblende schist strata, 

 which spread over a large part of northeastern Minnesota. On 

 the shores of Pelican lake. Rainy lake, Namekan lake, Vermilion 

 lake and many others of our largest bodies of water, there are ex- 

 tensive out-crops of these rocks. Their dip is at all angles, from 

 horizontal to vertical, but generally the latter. However, on 

 Rainy lake several anticlinals are seen, where the dip changes from 

 south to north, or vice versa. The general trend or strike of this 

 formation is that of all the stratified rocks of the region, i. e., 

 about north, sixty degrees east. 



It is only very recently that this formation has been proved 

 to be iron-bearing. But during the past few months samples of 

 good ore have been obtained from it in township 63 N., Range 12 

 W., north of the town of Ely. In sections 4 and 5 of this town- 

 ship the hornblende schist becomes charged with magnetite to such 

 a degree that it is apparently a fair quality of magnetic ore. No 

 analyses have yet been made of it. It may contain titanium. 



