PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 737 



Quartzyte. Hematite . ] 



irregularly in the quartz in certain places. This slide shows a small amount of 

 microcline(?) and apparently a small amount of another feldspar, and also a grain of 

 colorless to-urtiuilinc, which seems to he of secondary origin, since it surrounds several 

 small quartz grains. This tourmaline has a yellow or orange color of double refrac- 

 tion, and a strong polychroism, darker when it agrees with the horizontal thread. 

 It has n p in agreement with its elongation, and an imperfect cleavage parallel with 

 the cross section. One section. 



At/i: Pokegama (bottom of the Animikie.) N. H. w. 



No. 1526. QUARTZYTE. 



Pokegama falls; same place as the last 

 Ref. Annual Report, xviii, pages l.\ i;o. 



Meg. Shows another spottedness. Here the* rusty spots weather out and 

 produce a pitted surface on the quartzyte in which the round surfaces of the grains 

 are exhibited. 



Mic. Between the rounded quartz grains is much of a substance which is 

 isotropic, but transparent, clear and colorless, having some hematitic staining in the 

 form of dirty particles, as well as some indefinite microliths. Occasionally some of 

 this inter-granular, isotropic substance is replaced by, or at least charged with, coarser 

 crystalliths which appear to be actinolite, or both actinolite and mica. Still more 

 rarely a cleaved grain resembling feldspar is seen in the midst of the same substance. 

 Sometimes a dim translucency between crossed nicols appears in small spots, 

 denoting imperfect crystallization. This substance is so abundant sometimes that 

 the rounded quartzes that lie in it do not come into contact. It everywhere acts as 

 a filling which surrounds them. While in general the rock consists of coarse clastic 

 quartz, there are roundish spots or areas where this substance prevails, and this is no 

 doubt the cause of the megascopic spottedness mentioned. The microscopic aspect 

 is seen in figure 3, plate III. There seems to be no way to interpret this structure 

 other than to refer it to fine volcanic ash accumulated cotemporary with the fonna- 

 tion of the rock. 



If this be volcanic ash it is comparable with the similar phenomena seen at the 

 eastern end of the Mesabi range in the vicinity of Gunfiint lake, and with the 

 volcanic phenomena reported on the Penokee range by Van Hise.* The trichiths 

 mentioned in No. 1521 do not appear in this rock nor in No. 1525A. One section. 



Aye. Pokegama (bottom of the Animikie). N. H. w. 



No. 1527. HEMATITE. 



Prairie River falls, S. E. J4 sec. 34, T. 56-25 W. 



Ref. Annual Report, xviii, pages 15, GO ; Bulletin vi, pages 120, 422. 



'' Hulli'lill il/llir <;<>,ln,li,;:l Nij'-ii-tl/ ')/ A nli-fii-ii , veil. iv. ].. 1:15. IHOii. 



*)', 



