604 THE GEOLOGY OF MINNESOTA. 



[Diabase. Granite. Schist. 



No. 926. DIABASE. 



N. E. y sec. 31, T. 63-17 W.; Bear narrows, Vermilion lake. 

 Kef. Annual Report, xv, pages 295, 389. 



Mfff. A fine-grained, dark-gray diabase, with some pyrite. 



Mic. The section shows a rock consisting essentially of plagioclase and augite. 

 The former is usually in lath-shaped forms and is considerably altered. The augite 

 is in polysomatic areas and in plates which have an ophitic relation to the feldspars. 

 The augite is also some altered, and secondary minerals have been developed through- 

 out the slide. These secondary minerals are mainly chlorite, hornblende, biotite and 

 quartz. Magnetite and pyrite also occur in the slide. 



One section. 



Age. Probably a dike cutting Archean rocks. u. s. G. 



No. 927. GRANITE. 



From the point near the centre of sec. 23, T. 63-18 W.; West bay, Vermilion lake. 

 Ref. Annual Report, xv, pages 295, 389. 



Meg. A medium-grained granite, composed of quartz, white to pink feldspar 

 and a dark mineral which appears to be largely chlorite. 



Mic. A granitic rock, composed essentially of feldspar, which is highly altered, 

 isolated quartz grains and chlorite. Epidote and magnetite are present. 



One section. 



Age. Archean. u. s. G. 



No. 928. CHLORITE SCHIST. 



" Gray wacke-like rock containing syenyte in lenticular patches, southwest corner sec. 9, T. 63-17;" Long 

 bay, Vermilion lake. 



Ref. Annual Report, xv, page 390. 



Meg. The specimens vary from a fine-grained, green, somewhat schistose, chlo- 

 ritic rock, with some feldspathic material, to a rock of a little coarser grain and 

 resembling somewhat a dark graywacke. 



Mic. The section shows a rock which is composed essentially of three minerals, 

 quartz, feldspar and chlorite. Tbe feldspar is considerably clouded by decay and the 

 texture of the rock is almost granitic. 



One section. 



Age. Archean. u . s. G. 



No. 929. BIOTITE SCHIST. 



N. E. y sec. 14, T. 63-18 W.; north shore of West bay, Vermilion lake. 

 Ref. Annual Report, xv, pages 296, 390. 



Meg. The specimen is a dark-gray, biotite schist of medium grain for such a 

 rock. 



