612 THE GEOLOGY OF MINNESOTA. 



[Gneiss. Oummingtonite schist. Granite. 



No. 955. GNEISS. (Granitoid.) 



From boulders in N. W. J sec. 26, T. 61-12 W.; north shore of Birch lake. 

 Ref. Annual Report, xv, pages a33, 334, 391. 



Meg. A medium-grained, dark-gray, granitic gneiss. 



Mic. A schistose rock appearing like a sheared granite, the grains being broken 

 and apparently granulated around the edges. The chief minerals are quartz, feldspar 

 and dark brown biotite. 



One section. 



Age. Boulders of Archean rocks. u. s. G. 



No. 956. GNEISS. (Hornblendw muscovadite? ) 



From boulders in N. W. % sec. 26, T. 61-12 W.; north shore of Birch lake. 

 Ref. Annual Report, xv, pages 333, 391. 



Meg. A dark-gray gneiss of medium grain. 



Mic. The section shows a somewhat confused aggregate composed essentially 

 of the following minerals: feldspar, biotite, hornblende, chlorite, magnetite and quartz. 

 The feldspar is in irregularly interlocking grains and commonly forms the back- 

 ground of the rock, this mineral holding the other minerals poikilitically. 



One section. 



Age. Boulders of Archean (?) rock. u. s. G. 



NO. 957. CUMMINGTONITE SCHIST. 



From boulders in N. W. % sec. 26, T. 61-12 W.; north shore of Birch lake. 

 Ref. Annual Report, xv, pages 333, 391. 



Meg. Similar to No. 950. 



Mic. This rock appears similar to No. 950, except that it (No. 957) is coarser 

 grained and the cummingtonite is of a greenish tint, is slightly pleochroic and is often 

 colored brownish, due to staining or alteration. 



Two sections. 



Age. Boulders of Archean rock. u. s. G. 



No. 958. GRANITE. (Breccia.) 



N. E. J4 S. E. M sec. 21, T. 61-12 W.; point on the north side of Birch lake. 

 Ref. Annual Report, xv, pages 333, 391; Annual Report, xvii, pages 195, 207. 



Meg. Irregular masses of dark -gray, fine-grained rock, inclosed in a cement of 

 rather fine-grained, light-gray to pinkish granite. 



Mic. The dark masses are composed of a granitic aggregate of hornblende, 

 feldspar, much of which is clearly plagiodase, and quartz. The cementing rock is an 

 ordinary biotite granite. The sections do not show the j unction of the two kinds of rock. 



Two sections. 



Age. Archean. u. s. G. 



