806 THE GEOLOGY OP MINNESOTA. 



[Black slate. Diabase. 



glassy, but tinted with a faint tint of rose red. It has no cleavage nor optical 

 anomalies, but irregular fissures cross it in all directions. Apparently one crystal 

 mass extends continuously over the whole slide. There are also a few small spher- 

 ules of delessite or thuringite. One section. 



Age. In the Pewabic(?) quartzyte. 



Remark. It is impossible to distinguish the species of this garnet, but its most 

 obvious characters seem to indicate either pyrope or almandine. Chemical analysis 

 only will determine the species. N. H. w. 



No. 1896. BLACK SLATE. 



S. W. J4 sec - 21, T. 65-4 W., near Paulson's camp. 

 Ref. Annual Report, xxii, page 12. 



Meg. Fine grained, magnetited, much crumpled, bedded, or sheeted. This is 



an isolated ridge of the Animikie(?) separated from the main mass by a high green- 

 stone range of Keewatin rocks. 



Mic. In a background of fine interlocking quartz and feldspar are much 

 magnetite, and considerable cummingtonite* these all being in tine grains, having a 

 tendency to globular shapes. At the same time occasional crystals of some pyroxene 

 of much larger size embrace all the foregoing, poikilitically, including also numerous 

 globules that appear to be of the same pyroxene, though having independent orien- 

 tation. One section. 



Age. Perhaps jaspilitic slate of the Keewatin. 



Remark. While this rock is supposed to be a part of the Animikie, and grades 

 petrographically into the iron-bearing quartzyte at the mine about a mile further 

 south, which is the ore of the region, yet it grades into the rocks (in the field work 

 often called muscovado) that resemble muscovadyte, and apparently into the true 

 muscovadyte which is a phase of the gabbro. Further study is needed in order to 

 separate, in this case, the modified Animikie from the modified Keewatin. N. H. w. 



No. 1898. DIABASE. 



From the hill at the west side of the outlet from South Fowl lake. 

 Ref. Annual Report, xxii, page 12. 



Meg. From the central part of the well-known dike which cuts the hill 

 vertically, visible in the cliff. 



Mic. The original augites, which preceded the feldspars, have been altered in 

 large part to a greenish, obscure, hornblendic substance. In general, however, 

 throughout the slide, there is a curious intergrowth of hornblende and pyroxene, each 

 having its characteristic extinction angle, the pyroxene being most frequently 

 plainly enveloped by the hornblende, as described in No. 1899. One section. 



Age. Manitou(?) N. H. w. 



* This is the mineral frequently known as griinerite, after the determination of Lane and Sharpless, but which, according 

 to the comparative analyses, as given by Hintze, should be called cummingtonite. 



