542 THE GEOLOGY OF MINNESOTA. 



[Granite. Syenyte. Gabbro. 



Mr;/. A rather fine-grained, crystalline, dark, brownish-gray rock, composed of 

 feldspar, biotite, hornblende, probably augite and a little quartz. 



NIC, M. E. Wadsworth's description of this section is as follows:* 



" The section is composed of feldspar (largely plagio<-lx<'), n/it/ite cores, and 

 secondary </nnifz, biotite, hornblende, inat/netife, and microliths. The augite cores are 

 surrounded by and pass into both biotite and uralite. The rock is now a quartz- 

 biotite-dioryte, but the writer has no doubt that it is simply an altered diabase to 

 which its augite and feldspar ally it." 



Two sections examined. 



Age. Cabotian. a. s. o. 



No. 779. GRANITE (icitli i.iitit<- <m<l linrniili'inlej. 



Same locality as No. 777. 



Re/. Annual Report, x, pages 100, 101. 



Meg. A rather fine-grained, reddish, granitoid rock, composed of feldspar, 

 quartz, hornblende and biotite. 



Mir. The section shows a fine-grained granite composed essentially offeldx/xir, 

 which is much clouded and frequently reddened, quartz, hnrnli/i-nde and fiinfite. 



One section examined. 



Age. Cabotian. r. s. G. 



No. 780. SYENYTE(?) (iritl tuujiir). 



Same locality as No. 777. 



Ref. Annual Report, x, pages 100, 101; Bulletin ii, page 85. 



Meg. A medium-grained granitoid rock, composed of feldspar, a little quartz 

 and black minerals. Similar to No. 776. 



Mir. M. E. Wadsworth's description of this rock is as follows :f 



"It is a yellowish-gray granitoid rock, composed at feldspar, magnetite, biotite 

 and hornblende. It is so altered that the transition is complete, except in the case 

 of a few pyroxene grains, so as to form a quartz-dioryte, although it contains much 

 orthoclase and some biotite and might thus be styled a granite. The orthoclase, 

 tjnnrtz, biotite and hornblende all appear to be secondary, as are probably the 

 numerous microliths by which they are traversed." One poor section examined. 



Age. Cabotian. u. s. G. 



No. 781. GABBRO(?) (with' quartz). 



Portage between L and Wind lakes; probably in E. J^ sec. 11, T. 63-5 W. 

 Ref. Annual Report, x, page 101: Bulletin ii, page 97. 



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

 biotite and a little quartz. 



'Bulletin ii, p. 120. 

 t Bulletin U, p. 85. 



