PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 845 



Taconyte. Quartzyte.] 



triangular spaces embraced between the roundish taconite grains, which are filled 

 with much coarser secondary quartz interlocked in apparently the same manner as 

 in the grains. The difference of texture, while marking the outlines and size of the 

 original grains, seems to indicate that the pebbles (taconyte grains) were deposited 

 in their present places prior to the introduction of the intergranular silica. Lastly 

 there are narrow strips or belts of fibrous silica, apparently arranged along cracks, 

 to which they stand perpendicular, which, having a negative elongation can correctly 

 be styled chalcedony, the rest of the silica, composing the interlocking mass in general, 

 both coarse and fine, being simply ordinary quartz, so far as observed. 



In this slide are also two grains of distinctly different kind, being of quartz of 

 foreign origin, which must have accumulated when the taconitic " greensand " was 

 brought together. One is angular and has a single orientation. It lies in the midst 

 of fine interlocking quartz, with which it has no sympathy, but has a surrounding 

 coating of iron ore. The other is a round pebble of coarse interlocking quartzyte. 

 It has distinct boundaries as a pebble, and also lies in the matrix of fine interlocking 

 quartz. It is also coated with a film of iron, and iron enters somewhat within it. 

 It is suddenly and boldly set off from the matrix in which it lies. So far as they go 

 these foreign grains indicate a fragmental manner of accumulation for the original 

 globular constituents of this rock. One section. 



Age. Animikie. 



h'ciiidiii. The roundish taconitic grains in this rock, which is now almost 

 wholly of quartz, are of two sorts: (1) Very fine or flinty, siliceous, resembling the 

 quartz-feldspar mosaic of devitrified glass, and undistinguishable from flinty masses in 

 the Animikie at Gunflint lake, as those embraced in No. 312, and like the flint of Nos. 

 1277 and 1295. (2) Irregularly shaped, but roundish, forms that are largely opaque 

 with iron and still more resemble devitrified glass, or lava sand. The latter is repre- 

 sented in figure 3, plate V. N. H. w. 



No. 2139. QUARTZYTE. 



Mountain Iron mine, Mesabi Iron range. 



Kef. Annual Report, xxi, page 160, rock c \ Annual Report, xxiv, page 48. 



Mey. Greenish-gray, fine Pokegama quartzyte, clearly striped parallel with the 

 usual sedimentary strike of the region. Lies below the iron-bearing strata. 



Mir. This quartzyte appears quite different from the foregoing from this 

 region. It is plainly of clastic origin and structure. The grains are angular, and, 

 while they plainly have a secondary growth which forms an interlocking mass, they 

 are not wholly of secondary date. Mingled with them are a few grains of striated 

 ft'/i/xjjdr and inicmrlitK' and of nmscooitv. There is in this rock no visible taconitic 

 structure. One section. 



Age. Auimikie. N. H. w. 



