522 THE GEOLOGY OF MINNESOTA. 



[Grit. Diabase. Schist. 



Mi<: A very tine-grained aggregate of quartz, probably some feldspar, chlorite, 

 niuscorite, epidotc, pijrite and other opaque grains. Scattered through the section are 

 angular quartz grains of considerably larger size than the main mass of the minerals. 



One section examined. 



Age. Keewatiu; probably Upper Keewatin. u. s. G. 



No. 741. GKIT. 



Same locality as No. 740. 



Ref. Annual Report, x, pages 91, 93, 94. 



Metj. A fine-grained, gray grit made up largely of quartz and feldspar. 



Mic. The section is composed largely of quartz and feldspar grains. The 

 quartz is in sharply outlined, angular, sub-angular and sub-rounded grains; those 

 which show rounding are, however, not common. The feldspar grains are less dis- 

 tinct than those of quartz, and are much clouded and altered to a kaolinic mass, which 

 material, also at times, extends between the different grains of the rock. Calcite is 

 common; chlorite and pyrite also occur, and there are a few small rock fragments 

 probably of quartz-porphyry. 



One section examined. 



Aye. Keewatin; probably Upper Keewatin. n. s. G. 



No. 742. DIABASE. 



A dike cutting the conglomerate of Ogishke Muncie lake; N. W. y N. E. % sec. 26, T. 05-0 W. This dike 

 is ten feet wide, and it strikes 10 south and east. 

 Ref. Annual Report, x, pages 91, 93. 



Mey. A fine-grained, dark, greenish-gray diabase. 



Mic. In texture the section approaches a gabbro, but is still to be referred to 

 diabase. The chief minerals are plagiodase, augite and magnetite. In general the 

 first mineral is decidedly kaolinized, although in places it is quite fresh. Equal 

 extinction angles in sections normal to 010 are as high as 29. The augite is altering 

 to uralite and chlorite, and in these alteration areas is a little secondary quartz. 

 Apatite needles occur and are especially common in some of the alteration areas. 

 A little pyrite is present. 



One section examined. 



Aye. Probably Keweenawan. 



No. 743. SCHIST. 



N. E. 14 N. E. y sec. 26, T. 65-6 W; near Ogishke Muncie lake. 

 Ref. Annual Report, x, pages 91, 95. 



Meg. A roughly schistose, rusty weathering, soft rock which effervesces rather 

 readily with cold hydrochloric acid. It is fine grained, but in places is distinctly 

 crystalline like marble. 



