818 THE GEOLOGY OP MINNESOTA. 



[Mica schist. Albite and microeline. Gnuiss. 



Mic. It is not distinguishable from the last, except that it contains more chlo- 

 ritized hornblende. One section. 



Aye. Archean (granitized schist). N. H. w. 



No. 1996 i. MICA SCHIST. ( Subgranitized. ) 



Same place as the last. 



Ref. Annual Report, xxiv, page 4. 



Meg. With many granitic segregations within the mica schist, there are also 

 intermediate rocks, or stages of transition from schist to gneiss, and apparently to 

 granite. This represents one of the intermediate stages. . 



Mic, The rock is completely crystalline, but not with a new interlocking 

 structure; on the other hand the grains are subround and small, though exactly fitting 

 and filling all the spaces in which they lie. The feldspar* are much decayed by 

 weathering, but the decay has attacked their borders first, leaving the central portions 

 fresh, when any portion is left unaltered. Tn general, this decay is uniform through- 

 out the whole grain. Thus their appearance in this respect is the reverse of that 

 presented by the "old feldspars" already mentioned in several granites. The rock 

 contains much quartz and a considerable quantity of chloritized hornblende. One 

 section. 



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



No. 1997. ALBITE AND MICROCLINE. 



Same place as No. 1994. 



Ref. Annual Report, xxiv, page 4. 



Meg. .Coarse pegmatyte, consisting of pink and white feldspars and of quartz. 



Mic. Tn a zig-zag course forms a vein in the schist, ascending a bluff twenty 

 feet high. The pink feldspar is clearly microclhie, and extinction on the basal cleav- 

 age of the white is 3. Specific gravity being 2.61, in Thoulet's solution, may be 

 somewhat increased by micaceous inclusions. It is probable, however, that the white 

 feldspar is either albite or oligoclase albite. The long, fine, twinning striations are 

 more like those of oligoclase than those of albite. One section. 



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



No. 1998. GNEISS. 



N. V.. > 4 sec. 22 (north side), T. 63-17, Vermilion lake, near the same place as No. 1994, about four rods 

 west of the north-south section line between sections 22 and 23. 

 Ref. Annual Report, xxiv, page 4. 



Meg. Forms a knoll at the lake, shore, a dark gneiss, dipping north, evidently 

 a more massive condition of the schists of the vicinity. 



Mic. The darker color is due to the presence of more hornblende, which is also 

 accompanied by epidote. The alteration of the mostly non-interlocking feldspars, 



