PETKOGRAPHIC GEOLOGY AND DESCRIPTIONS. 633 



Greenstone. Magnetite schist.] 



No. 1022. GREENSTONE. ( Granular. ) 



Same place; same exposed surface. 

 Ref. Annual Report, xv, pages 327, 394. 



Meg. Similar to the last. 



Mic. I-^tiflote is here common. The feldspar is but little more common than 

 in the last, and is fragmental; that is, it is in scattered rounded pieces, not in angular, 

 and is sufficiently preserved to show its albite twinning. The green coloring matter 

 ischlofitic, in general, and sometimes hornblendic, in the latter case strongly pleochroic 

 and faintly doubly refracting, the changing colors of pleochroism being very light 

 yellow and pale green. Leuco.rene is abundant, and scattered in small grains through- 

 out the slide. A very little quartz in fine grains is seen. One section. 



Age. Archean (Lower Keewatin). N. H. w. 



No. 1023. GREENSTONE. (Dense, fine.) 



Same place and exposed rock surface. 

 Ref. Annual Report, xv, pages 328, 394. 



Meg. More firm, fine-grained, schistose in the same direction. Taken in the 

 midst of the schists above. 



Mic. This is an average rock of the series above described. It has scattered, 

 chloritized, fine feldspars rather scarce, distributed in a dark-green, structureless 

 matrix, containing chlorite, calcite, quartz, a little epidote, leucoxene and finer 

 feldspars. One section. 



Remark. This series of greenstones was collected for the purpose of studying the 

 minute transitions between a fine green schist (No. 1017), presumed to be of clastic 

 origin, and a coarser greenstone (Nos. 1022 and 1023), which, in the field, was assumed 

 to be of igneous origin. The conclusion arrived at was that they were all derived 

 from originally massive igneous rock, and that the fine schist (No. 1017) was formed 

 by shearing of a rock like a diabase. It is evident now, however, that one of these 

 assumptions must be erroneous. A subsequent microscopic examination of the 

 slides, followed by a review of their characters in the light of long study and 

 comparison with known altered diabases, leads to the conclusion that they are all 

 of clastic origin, and of the nature, primarily, of basic debris which was perhaps 

 tuffaceous, the supposed igneous rock (Nos. 1022 and 1023) being simply coarser 

 debris of the same sort as No. 1017. 



Age. Archean (Lower Keewatin). N. H. w. 



No. 1024. i MAGNETITE SCHIST. 



S. W. % sec. 23, T. 63-11. Julian Bausman's, east of Farm lake. 



Ref. Annual Report, xv, pages 328, 394; Annual Report, xix, pages 121, 127. 



Meg. The rock is fibrous, but dark with magnetite, blue black in color. 



