PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 929 



Quartzyte. Granite and amphiboly te.] 

 Taconyte. 



mingtonite it begins at points in the main greensand grain, involving certain of the 

 polygonal areas into which it is cut by the general cracking. 



6. It is apparent that the greensand is the source of the quartz, the cumming- 

 tonite and the iron ore, and that the quartz, gathering in the interspaces about the 

 greensand grains, is coarser than that in the areas of the grains themselves, because 

 of greater freedom of chemical transference in those open spaces. 



It seems to the writer that these features, and other facts mentioned in the 

 description of other rocks derived from the Mesabi Iron range, whether at Gunflint 

 lake or at Prairie River falls, indicate that the greensand was of the nature of a 

 ferruginous volcanic sand. This result is further discussed in Part III. N. H. w. 



No. 43S. QUARTZYTE. 



S. E. % S. W. % sec. 4, T. 58-16, Mesabi Iron range, near Biwabik. 

 Kef. Annual Report, xxii, page 127. 



Meg. Loose conglomeratic quartzyte with kaolin. 



Mic. Round grains of uniform size of clastic quartz are surrounded by a debris 

 which is probably of kaolinic nature which has been incorporated in the secondary 

 rim of quartz by which the rock is cemented and made firm. One section. 



Age. Pokegama quartzyte(?) (base of the Animikie). This rock may belong 

 to the Cretaceous instead of the Animikie. 



No. 47S. GRANITE AND AMPHIBOLYTE. 



S. W. y N. W. y sec. 35, T. 59-17, Mesabi Iron range. 

 Ref. Annual Report, xxii, page 127. 



Meg. Contact of granite on the Keewatin. 



Mic. The slide differs. One side consists almost wholly of green hornblende in 

 large crystals, but having a general parallelism of direction. With these are mingled 

 a little quartz (within the hornblendes), epidote and pyrite. The other part of the 

 slide, while containing also hornblende in form of elongated schistic fibres, consists 

 chiefly of much sliereifeldspars and interlocking quartz, with biotite. These feld- 

 spars (oligoclase, apparently), evidently of some anterior state, are now charged with 

 muscovite, some calcite, and occasionally contain quartz as secondary products, while 

 epidote also is in scattered grains. One section. 



Age. Archean. N. H. w. 



No. 53S. TACONYTE. (Greenland.) 



S. E. 14 sec. 4, T. 58-16, Mesabi Iron range. 



Ref. Annual Report, xxii, page 127 ; Bulletin x, page 68. 



Meg. Dark green, spotted-granular. 



Mic. The green primordial element is in one slide entirely broken up, and a 

 crystalline network is formed, consisting of the same actmolitic(?) ingredient as 



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