382 THE MAltQUETTE IKON-BEARING DISTRICT. 



grains have their greatest diameters in the same direction and have a 

 connnon extinction. In some shdes these parallel-arranged individuals cut 

 almost at right angles across the belts of magnetite and actinolite. These 

 facts suggest that the quartz is a secondary material, which has arranged 

 itself as demanded by the differential pressure. In other slides the quartz 

 has a peculiar irregular extinction, which reminds one of half-individualized 

 material. It appears unlike truly cherty or chalcedonic quartz, and yet is 

 unlike granulated, coarse-grained quartz. Where these peculiar varieties of 

 quartz occur the iron oxide is very largely magnetite, mostly in the form 

 of small crystals. In many slides the amphibole is decidedly i)leochroic, 

 and in some of them it gives beautiful blue and violet colors. The parti- 

 cles are so small that they could not be isolated, but it is thought that this 

 amphibole developed at the lower horizons because in the mingled nouclastic 

 and clastic material a wide variety of chemical elements were available. In 

 passing- from this area toward the Ishpeming and Negaunee area the quartz 

 shows more and more of I'earrangement and becomes more coarsely crys- 

 talline, grading into the irregularly laminated varieties which have been 

 denominated ferruginous chert. 



Cascade range. — Passiug uow to tlic cast cud of tlic soutliem belt, at the 

 Cascade range, in sees. 28, 29, 30, 31, 32, and 33, T. 47 N., R. 26 W. (Atlas 

 Sheet XXXII), we find the most extensive exposures of ferruginous chert 

 and jaspilite in the district. Also there are here complete sections from 

 the Ajibik quartzite below to the Goodi'ich quartzite above. Where the for- 

 mation has considerable width, as in sec. 28, the lower horizons of the 

 formation are the typical ferruginous chert, but as the Goodrich quartzite is 

 appn)ached the rock, as usual, becomes typical jasper. In the W. ^ sees. 29 

 and 32, and in sees. 30 and 31, where there is only a comparatively narrow 

 belt of the Negaunee formation between the Ajibik quartzite and the Good- 

 rich quartzite, the whole of the formation is typical banded jasper. It is 

 this locality which strongly suggests that the position of the iron-formation 

 rocks with reference to the overlying Goodrich quartzite, rather than the 

 particular horizon of the formation, determines whether the rock is mainly 

 ferruginous chert or jaspilite; for in sees. 28 and 33 the same horizon is fer- 

 ruginous chert which a mile or two to the west is typical banded jasper. 



