PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 927 



Flint. Taconyte.] 



ROCKS COLLECTED BY J. E. SPURR. 



No. 37S. FLINT. 



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

 Ref. Annual Report, xxii, page 127 ; Bulletin x, page 53. 



Meg. Gray, fine, with calcite. 



Mic. Very fine mosaic of quartz (and feldspar?) interlocking, interspersed 

 sparingly with calcite, which also crosses it in veins, accompanied by a little hematite. 

 One section. 



Age. Animikie (iron-bearing member). N. H. w. 



No. 39S. TACONYTE. 



Same place as No. 37S. 



Ref. Annual Report, xxii, page 127 ; Bulletin x, page 53. 



Meg. Light-green, spotted, granular taconyte. 



Mic. In a framework of interlocking quartz of the typical character are many 

 roundish, greenish-yellow areas, which are not in crystalline condition (at first), but 

 simply amorphous, isotropic aggregates. These are crossed by numerous irregular 

 cracks, and along these cracks, in other grains, it is seen that a kind of change is set 

 up. This change progresses irregularly, frequently appearing in isolated points in 

 the yellow mass (figure 53) and forming more transparent, finely crystalline nests. 

 These nests multiply and also enlarge, such enlargements taking on a radial, or 



FIG. 63. GKEENSAND IN NO. 88S. 



spherulitic structure, thus converting the whole original grain into a finely reticu- 

 lated and radial network of fine, fibrous, crystalline matter. Many such spots are 

 wholly changed to this network, others are in process of change, and others show 



