440 THE CRYSTAL FALLS lEGN-BEARING DISTEIGT. 



calcite. Magnetite, ilmenite, and limonite are usually rather abundant. 

 Pyrite also occurs in a few grains in nearly every slide. The differences in 

 color depend mainly upon the relative proportions of the chlorite and nius- 

 covite, the former being characteristic of the dark-colored, the latter of the 

 light-colored, rocks. The very dark-green or black varieties contain also 

 an opaque and probably organic pigment in very minute particles. The 

 quartz and feldspar grains are usually very small and irregularly shaped. 

 The larger, however, of which a few occur in the slides from the less com- 

 pressed rocks, have well-rounded contours. In other cases extremely 

 flattened and strung-out lenses composed of many small particles represent 

 what were doubtless originally single clastic grains. 



Two varieties of cleavage are well illustrated in the thin sections, 

 namely, that caused by the parallelism of the component minerals, and 

 " ausweichungs-clivage." The former is characteristic of the coarser- 

 grained varieties, and the latter of the finer grained, where the direction of 

 pressure has made a large angle with the bedding. In some cases the little 

 leaves of muscovite outline parallel and equal folds, less than 0.2 mm. from 

 crest to crest, each of which is ruptured, sometimes with slight displace- 

 ments, sometimes with none, entirely across the slide. The structure is most 

 distinct in the red phyllites, in which the fractures and the arrangement of 

 the muscovite plates are clearly outlined by the ferruginous stain. Each 

 kind of cleavage in a different way tells the story of extreme pressure. 



SECTION V. THE HEMIiOCK FORMATION. 



The Mansfield formation of the Michigamme Mountain area changes 

 along the strike into rocks of an entirely different character, which, as 

 already said, have been named the Hemlock formation. 



DISTRIBUTION, EXPOSURES, AND TOPOGRAPHY. 



The Hemlock formation in the Fence River area consists of several 

 varieties of schists which occupy a belt between 2,000 and 3,000 feet in 

 width between the dolomite on the west and the Grroveland formation on 

 the east. The best exposures occur on the two river sections already 

 referred to (p. 431), but outcrops are by no means lacking elsewhere. At 

 the northwest corner of the area, in sec. 6, T. 45 N., R. 31 W., the schists 

 are found striking N. 60°-70° W., and dipping northeast about 40°. East 



