692 THE GEOLOGY OP MINNESOTA. 



[Diabase. Zirkelyte. 



of flint, or devitrified rhyolite (No. 1277). There are also several that are perfectly 

 isotropic, greenish gray in common light, but in convergent light on lowering the 

 lower nicol there appears a mesh or maze of very fine spicules and crystalliths, 

 which are also probably a result of devitrification. One section. 



Age. Animikie. 



Remark. This rock, although not seen in situ, is distinctly allied to the rock 

 No. 1319, in containing, amongst a prevalent sand of round quartz grains, a few grains 

 of devitrified glass, or aporhyolyte. There is here a strong suggestion that the 

 pre-Animikie surface was covered, to a greater or less extent, by volcanic rocks which 

 furnished this debris. These rounded pebbles of devitrified glass, although consisting 

 now largely of fine secondary quartz, and in that respect resembling some parts of 

 the taconyte of the Animikie, are free from iron. This slide is illustrated by figure 

 9, plate II. N. H. w. 



No. 1323. DIABASE. 



Top of the hill (or ridge running east and west) north of Animikie bay, Gunflint lake. 

 Kef. Annual Report, xvi, pages 78, 121. 



Meg. Gabbro like, sometimes porphyritic like No. 1314. 



Mir. The magnetite, which is in crystals and skeleton crystals, cuts the augite, 

 and slightly the feldspar. The rock is weathered. Decay in patches in the feldspars 

 has produced apparently a mica which is near muscovite. One section. 



Age. Sill in the Animikie. N. H. w. 



No. 1324. ZIRKEI.YTE. 



Near the diabase contact, near the top of the ridge north of Animikie bay, Gunflint lake ; same place as 

 the last. This underlies the diabase sill. Compare No. 1327. 

 Ref. Annual Report, xvi, pages 78, 121. 



Meg. Flinty lower part of a diabase sill. 



Mic. The slide consists entirely of the same fine-grained, flinty substance 

 already mentioned, more or less clouded by magnetite and by belts of radiating 

 trichites, the latter being in the main arranged along fissures, but sometimes disposed 

 in radiating clusters in the mass of the rock. There is also another coarser crystal- 

 lization, consisting of a highly doubly refracting mineral, apparently pyroxene or 

 adinolite, which along a certain boundary is abruptly separated from the finer rock, 

 but which in another part of the slide graduates into the finer, showing that they 

 have a similar origin. These coarser crystalliths graduate into finer and finer 

 needles, sometimes forming four-armed black crosses which polarize near the point 

 of crossing, but which, where separated, can be seen to blend into the finer trichites 

 and are lost in the finer mesh. This fine crystallization, whether polarizing or not, 

 is embraced in a fine siliceous ( ?) granular background the body of the so-called flint 



