358 THE GEOLOGY OF MINNESOTA. 



[Granite. Schist. 



with many microscopic crystals, appears in conspicuous grains. It has coarse irreg- 

 ular cleavages, and a faint rose tint. 



One section. 



Age. Archean (Coutchiching). N. H. w. 



No. 418. GRANITE. 







Location not exactly known, but somewhere on Outlet bay, east side, on Vermilion lake. 

 Bef. Annual Report, ix, page 101; Annual Report, x, page 17. 



Meg. Gray or flesh -red, medium -grained. 



Mic. Orthoclase (kaolinized), microcline, quartz, biotite, compose this rock. 



One thick section. 



Age. Archean (igneous). N. H. w. 



No. 419. BIOTITE SCHIST. 



Exact location unknown. At some point in the schist area of Outlet bay of Vermilion lake. 

 Ref. Annual Report, ix, page 101. 



Meg. Compact, fine-grained, gray schistose. 



Mic. The thick section only warrants the statement that this rock consists of 

 a dense, markedly schistose aggregate of clouded feldspar, biotite, quartz and chlorite. 

 One section. 

 Age. Archean (Coutchiching). N. H. w. 



No. 420. BIOTITE SCHIST. 



Location not exactly known, but near the southern limits of Outlet bay. 

 Ref. Annual Report, ix, page 101. 



Meg. Softer mica schist, fine and glistening. 



Mic. With much fresh and quartz-like feldspar appears biotite. After consid- 

 erable search amongst these translucent grains, not one could be found that could be 

 said unqualifiedly to be quartz, but the greater part of them gave, in convergent 

 lig 1 t, characteristic figures showing a biaxial mineral. These feldspars, differing 

 remarkably from those in some of these schists, are believed to be of secondary 

 origin, dating probably from the pressure and shearing of the original material. 

 The much-clouded feldspars, which sometimes prevail, but are often seen in the same 

 slide with the glassy forms, are therefore to be classed with the original elements of 

 the rock. A striated, original grain, cut perpendicular to n f , shows an angle of 10 

 between the optic plane and the albite macles, indicating oligoclase, the grain being 

 in the reverse position from that required by Fouque's tables. 



One section. 



Age. Archean (Coutchiching). N . H . w. 



