924 THE GEOLOGY OF MINNESOTA. 



[Mica schist. Graywacke. Amphibolyte. 



No. 387H. MICA SCHIST (with biotite). 



Partridge river, N. E. % S. W. J sec. 9, T. 58-14. 



Ref. Annual Report, xvii, pages 90, 137. (Compare No. 1708.) 



Meg. Dark, silico-argillaceous and micaceous. 



Mic. There is an interlocking fine quartz as a basis of this schist, which was 

 later in its granular deposition than the mica which cuts the quartz and maintains 

 its form in the granular structure. But there are larger, later micas, which give 

 way to the quartz. These are colorless, and appear to be of Muscovite. One 

 section. 



Age. Animikie. N. H. w. 



No. 389H. GRAYWACKE(?) ( Subcrystalline. ) 



Near the centre of S. E. ^ sec. 8, T. 59-14. 

 Ref. Annual Report, xvii, pages 91, 137. 



Meg. Gray, gneissoid, having the aspect of an igneous rock. 



MicS A fine-grained rock, consisting largely of old feldspars, has been perme- 

 ated by secondary fresh quartz and fresh feldspar (near oligoclase). Some shreds of 

 hornblende are changed to chlorite, while fine Muscovite scales permeate thickly the 

 original feldspars. There are also several grains of sphene and of biotite. One section. 



Age. Keewatin (regenerated). N. H. w. 



No. 390H. GRAYWACKE. (Fine.) 



S. E. 14 sec. 11, T. 59-14, Mesabi range. 

 Ref. Annual Report, xvii, pages 91, 137. 



Meg. Fine, gray, micaceous. 



Mic. This rock is finer, but is essentially the same as No. 389H; it shows also 

 hornblende; and Muscovite and biotite are intimately associated. The feldspars have 

 the form and size of clastic debris. Some of the larger muscovites enclose poiki- 

 litically several of the small old feldspars. One section. 



Age. Keewatin. N. H. w. 



No. 397(a)H. AMPHIBOLYTE. 



S. E. y N. E. Yi sec. 26, T. 61-12, near Birch lake. 

 Ref. Annual Report, xvii, pages 93, 137. 



Meg. Hornblendic quartzyte. 



Mic. The slide consists almost entirely of hypersthene, in which are embraced, 

 however, poikilitically, a number of round, small grains of quartz, and others of 

 about the same size and shape of a highly refractive mineral resembling olivine, and 

 a few of magnetite. This gives place to a fibrous divergent network of some amphi- 

 bole, which in turn passes into a distinct cummingtonite (often known as grilnerite), 

 having multiple twinning. At the extreme other end of the slide is another crystal 



