540 THE GEOLOGY OP MINNESOTA. 



[Granitf. GaM.ro. 



No. 775. GRANITE (with horn blende mul biotite). 



Southeast end of Duck lake; S. W. 1,4 S. W. % sec. 2, T. 63-5 W. "At the southeast end of Duck lake 

 No. 77.3 lies on No. 775, which is the well-known and so-called 'red granite.' This lies in even and regular beds 

 of four to eight inches (or in beds of three to four feet), dipping south, amounting in all to about twenty feet, 

 the rock No. 773 being unconformable on it, but intimately cemented to it, as at Rice point. Over both of these, 

 further toward the southeast, No. 774 comes in again." 



Ref. Annual Report, x, pages 100, 101. 



Meg. A fine-grained, pink, granitoid rock, composed of pinkish feldspar, quartz, 

 biotite, hornblende. There are a few larger feldspars which give a sub-porphyritic 

 aspect to the rock. 



Mic. The section shows a fine-grained granite. The minerals are feldspar, 

 fjitftrfz, biotite, hornblende and magnetite. The feldspar is somewhat reddened and 

 much clouded; it is probably largely orthoduse. 



One section examined. 



Age. Cabotian. u. s. G. 



No. 776. GRANITE (icit/i 



Portage between Duck and L lakes; probably in S. W. HS.W.% sec. 2, T. 63-5 \V. 

 Ref. Annual Report, x, pages 100, 101; Bulletin ii, pages 96, 97. 



Meg. A medium-grained, brownish-gray, granitoid rock, composed of feldspar, 

 quartz, biotite, hornblende and probably augite. 



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



"Has its section composed of partially altered </ia//ag<>, fehhpm-. magnetite, and 

 secondary quartz, hornblende, biotite, etc. The diallage is filled with the usual black 

 needles and grains, which also occur abundantly in the feldspar. Part of the feldspar 

 appears to be of a secondary origin, while numerous ainphibolemicrolittis of secondary 

 origin extend through the quartz and feldspar. Fluid cavities occur in the quartz. 

 The hand specimen is a brownish-gray, granitoid or dioritic rock, with tabular pinkish 

 feldspar. It shows surface weathering." 



No section found. 



Age. Cabotian. u. s. G. 



No. 777. GABBRO. (Gnnmli/ic: 



L lake, probably just at the east of the portage to Wind lake; probably near the centre of N. W. J| sec. 11, 

 T. 63-5 W. "At the point where the portage leaves L lake is a bluff at the left, made up of the following (Nos. 

 777-780): 



"No. 777. A characteristic gabbro, seamed by red syenyte, and weathering nearly white, porphyritically, 

 so as to appear much like No. 773. This passes downward into 



" No. 778, which was obtained about thirty-five feet below the top of No. 777 and near the next. This is 

 apparently a form of the gabbro, when in closer contiguity with the sedimentaries, and has been penetrated by 

 minerals from them. It is finer grained than No. 777, and darker, but also seems to have orthoclase and mica. 

 These together make a thickness of about forty -five feet, from the top of the bluff downward. They are one^in 

 structure, dip and general characters. They dip south in heavy layers at an angle of about 30. 



"No. 779. Red syenyte, unconformable under No. 778, showing about fifteen feet. What appears like 

 bedding in No. 779 may be coarse jointage, as there are two sets of planes, one set being perpendicular to the 

 bedding of the gabbro overlying, and the other crossing it so as to have a dip south of about 70. 



* Bulletin U, p. ! 



