PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 543 



Granite. Quartz-porphyry.] 



Mic. M. E. Wadsworth's description of this rock is as follows:* 

 "A gray crystalline granitoid rock, composed of gray feldspar, biotite, hornblende, 

 etc. Its section is similar to the preceding No. 776, but it has few microliths. The 

 diallage lias fewer inclusions than that of No. 776, and is largely altered to horn- 

 blende and biotite. The quartz is quite abundant, and the biotite is largely 

 associated with and surrounds the magnetite. The analysis by professors Dodge 

 and Sidener gave the following result:" 



SiO 2 53.43 



A1 2 O S 13.81 



Fe 2 s 5.08 



FeO z 9.86 



MnO trace 



CaO 8.25 



MgO 4.64 



Na 2 O 2.51 



K 2 1.12 



H,O 0.27 



Total 98.97 



Two poor sections examined. 



Age. Cabotian. u. s. G. 



Remark. " Along the north side of Wind lake, these formations, the red and 

 the gray, are somewhat interbedded, and so brecciated and mixed that the bluffs are 

 spotted pi-omiscuously with the two colors. Sometimes, also, they seem to have 

 been fused and blended into a rock that is neither red nor gray." N. H. w. 



No. 782. GRANITE (ivith biotite). 



Southeast side of Wind lake; perhaps in S. E. % sec. 15, T. 63-5 W. 

 Ref. Annual Report, x, page 101. 



M<-<j. A fine-grained, granitoid rock, pinkish-gray in color, composed of feld- 

 spar, quartz and biotite.' 



Mic. The section shows a fine-grained granite, composed of quartz, feldspar, 

 liiolite, magnetite and a little chlorite. Most of the feldspar is considerably clouded 

 and appeal's to be orthodase; some of the least clouded grains have the characters of 

 a plagioclase near olir/odase. One section examined. 



Age. Cabotian. u. s. G. 



NO. 783. QUARTZ-PORPHYRY(?) 



Southeast side of Wind lake; perhaps in S. E. % sec. 15, T. 63-5 W. " This is one of the metamorphosed 

 sandstones of the Cupriferous." 



Ref. Annual Report, x, pages 101, 121. 



Meg. A very fine-grained, granular rock of a flesh color. The minerals appear 

 to be quartz, feldspar and biotite. The rock looks much like a fine-grained feldspathic 

 quartzyte. 



*Sulletin ii, p. 97. 



