418 THE CEYSTAL FALLS lEON-BEAEING DISTRICT. 



siiddenly cut off, as if by faulting, or taper to thiu edges, or occur in sepa- 

 rated pebble-like forms. Neighboring lenses and fragments of bands are 

 most frequently roughly parallel with one another, but often they are 

 jumbled together in the greatest confusion. They no doubt represent an 

 original more continuous banding, which has suffered brecciation. Masses 

 thus shattered are also traversed and cemented by numerous small veins 

 filled chiefly with quartz, chalcedony, and specular hematite. The posi- 

 tions in which the separated patches of the Groveland formation now 

 survive, namely, in and near the bottoms of synclines, and therefore at the 

 points where sharp turning and crowding together have taken place, suffi- 

 ciently explain the extensive brecciation observed in these brittle beds. 



Very jDrevalent in all the varieties of the first kind of rock, in massive, 

 banded, and brecciated alike, is the occurrence of some of the constituents 

 in small roundish spots, which give to the whole formation a very detrital 

 aspect. In the quartzitic phases, as well as in the most ferruginous bands, 

 the eye recognizes, besides the little grains of clear quartz, which seem to 

 be unquestionably detrital, numerous small dots of blue hematite and bright 

 red dots of jasper. These are more abundant in some layers than in others, 

 but seem never to be entirely absent, and are exceedingly characteristic of 

 the formation wherever found. 



In a few localities the iron constituent is almost entirely in the form of 

 little micaceous scales of specular hematite, which have a parallel arrange- 

 ment. Hematite-schists, however, are not very common. The best exam- 

 ples occur in the northern part of sec. 36, T. 42 N., R. 30 W., along the 

 northern syncline. 



The second kind of rocks of the formation, the griinerite-schists, have 

 been found in small thickness and in one locality only, namely, in the 

 southern parts of sec. 33, T. 42 N., R. 28 W., where they underlie, in a 

 series of small anticlines and synclines, banded siliceous beds composed of 

 quartz and magnetite or martite. 



Under the microscope the essential constituents of the first or prevalent 

 kind of rock of the Groveland formation are quartz, magnetite, martite, and 

 hematite. With these, much smaller quantities of chlorite, epidote, and 

 apatite are generally associated as accessories. Of rarer occurrence are 

 calcite and probably siderite, sericite, tremolite, grlinerite, pyrite, limonite, 

 chalcedony, I'utile, titanite, tourmaline, microcline, and plagioclase. 



