MANSFIELD SCHISTS IN FELCH MOUNTAIN EANGE. 413 



the specimens are of fine-grained mica-schists, the color of which varies 

 from hght to dark, according as muscovite or biotite is the predominant 

 mica. Grarnets, in some locahties, are very abundant, especially near the 

 contacts with intrusives. It appears from the records of explorations that 

 thin seams of jaspery iron ore inlerlaminated with the schists have been 

 encountered in occasional drill holes and test pits, but no specimens of such 

 occurrences have been obtained. Their existence is of interest, as showing 

 the likeness in an important character of these more altered rocks with 

 the slates occupying the same relative position in the Iron Mountain and 

 Norway areas. 



The outcrops and specimens are frequently well banded in lighter and 

 darker layers, the color banding in some cases not coinciding with the 

 schistosity. Just south of the Groveland mine, in a test pit which was 

 sinking at the time of my visit, the color bauds which mark the true strati- 

 fication, as shown by the contact with the underlying dolomite, are closely 

 crumpled and cut by the foliation of the rock, which is much the more dis- 

 tinct of the two structures. 



Near the contact with the overlying Groveland formation the mica- 

 schists become both more siliceous and more ferruginous, and there is 

 accordingly a distinct passage between the two formations. This does 

 not necessarily signify a transitional character in the original sediments, 

 biit ma)^ be altogether due to the downward transportation of silica and 

 iron from the upper rock. 



The mica-schists are generally very tender rocks, and the material 

 on the dumps of test pits sunk in them is usually far gone in decomposi- 

 tion after a few years' exposure to the weather. From even the freshest 

 specimens the little flakes of mica often rub off" on the fingers. Where 

 penetrated by intrusions, however, as in sec. 35, T. 42 N., R. 30 W., and in 

 sec. 31, T. 42 N., R. 28 W., they become very much harder. 



Under the microscope the rocks of this formation are seen to be in the 

 main thoroughly crystalline, though very fine-grained, aggregates of biotite, 

 muscovite, chlorite, quartz, and feldspar, with the iron ores, rutile, tourma- 

 line, and apatite as the accessories. Garnets are abundant in some of the 

 sections, and with these also occur actinolite, epidote, titanite, and an unde- 

 termined colorless amphibole in stout single prisms. In the eight thin sec- 

 tions which I have examined from this formation I have found no material 



