UPPER HUEONIAN^ OF FELCH MOUNTAIN EANGE. 425 



upper schists and quartzites continue their southeastward strike without 

 deviation. 



These general relations indicate that the ferruginous mica-schists and 

 quartzites are part of an upper series which overlies unconformably the 

 Groveland and all the lower formations. This series has not been found 

 elsewhere in the Felch Mountain area. 



PETROGRAPHICAL CHARACTERS. 



The rocks of this formation, as seen in the outcrops, are principally 

 soft and deeply iron-stained mica-schists in which occur frequent thin beds 

 of ferruginous and micaceous quartzite. 



Under the microscope the schists are composed mainly of biotite, 

 quartz, muscovite, and magnetite. Chlorite, as an alteration product of the 

 biotite, is frequently abundant, and garnets also occur in some sections. 

 These schists are much coarser in grain than those of the Mansfield forma- 

 tion, and are wholly crystalline. No clastic material has been recognized 

 in the thin sections. 



The quartzites also are thoroughly recomposed rocks, without recog- 

 nizable clastic particles. Quartz is the most abundant constituent, and with 

 it muscovite, biotite, and magnetite are constantly associated. The micas 

 and the magnetite are frequently inclosed in a background of large inter- 

 locking quartz grains, which is very similar to the background of the Stur- 

 geon quartzite. Such inclosures lie in general alignment throughout the 

 thin sections, but, unlike many of the inclusions of the Sturgeon quartzite, 

 they seem not to be clastic particles but to have crystallized in place. In 

 one slide among the inclusions in the large quartzes of the background is a 

 colorless isotropic substance, of low refraction, occurring in large polygonal 

 areas, but without definite crystal form. It is usually stained with limonite, 

 which has penetrated ft'om the margins along straight lines, as if following 

 cleavages. This interesting mineral, which is certainly not garnet, and 

 probably not opal, deserves further investigation 



The rocks of the upper series, like those of the lower series, are greatly 

 altered. From their mineralogical composition and structure it is evident 

 that as originally deposited they consisted of beds of mud separated by 

 thinner beds of sand. But as they now stand they have been as greatly 

 changed from their original condition as the bedded rocks below. Also, 



