616 THE GEOLOGY OP MINNESOTA. 



[Granite. Dioryte. 



Mic. Quartz arid feldspar make up most of the rock. The latter mineral is 

 usually clouded by alteration and is sometimes reddened. Magnetite is present, and 

 there are alteration products, chief among which is chlorite. 



One section. 



Age. Archean. u. s. G. 



No. 967. GRANITE. (Epidotic.) 



North side of sec. 21, T. 61-12 W.; bay on the north side of Birch lake. Occurs in the form of a dike cutting 

 coarse granitic rock. 



Ref. Annual Report, xv, pages 336, 391. 



Meg. A medium-grained, reddish granite. 



Mic. The section shows much feldspar, considerably clouded, and some epidote, 

 hornblende, chlorite, magnetite and quartz. 

 One section. 



Age. Archean. u. s. G. 



No. 968. GRANITE. (Hornblendic. ) 



Near the same place as No. 967. 



Ref. Annual Report, xv, pages 336, 337, 391. 



Meg. A rather coarse-grained, gray granite. The specimen is crossed by a 

 band of lighter color and finer grain. 



Mic. The essential minerals of this granite are feldspar, quartz, hornblende 

 and biotite. Chlorite, epidote, sphene and magnetite also occur. 



One section. 



Age. Archean. u. s. G. 



No. 969. DIORYTE. 



From a dike, eighteen inches wide, in theS. E. J^ sec. 29, T. 61-12 W.; Birch lake. 

 Ref. Annual Report, xv, pages 337, 391; vol. iv, page 261. 



Meg. A medium-grained, greenish rock, composed largely of hornblende. It is 

 crossed by a vein-like form of rusty, porous, feldspar rock. 



Mic. The dark portion of the rock is composed very largely of green horn- 

 blende, while the vein of feldspar rock is made up of much clouded feldspar. 



One section. 



Age. Archean. u. s. G. 



No. 970. DIORYTE. 



Schistose part of same dike as No. 969. 

 Ref. Annual Report, xv, pages 337, 391. 



Meg. A fine-grained, dark-gray rock, with coarser feldspars. 

 Mic. The section shows a rock composed essentially of green hornblende and 

 more or less altered feldspar. Sphene is common. One section. 



Age. Archean. Ug s . G> 



