PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 565 



Sandstone. Quartzyte. Granite.] 



Mir. The section is too thick for study. The rock is made up of water-worn 

 quartz grains which frequently are enlarged. Between the grains there is some 

 dust-like red (hematite) and gray material. 



One section. 



Age. Potsdam. u. s. G. 



No. 837. SANDSTONE. (Red.) 







Fragments from 205 feet below the surface;" from the deep well at the Washburn C mill, Minneapolis. 

 Ref. Annual Report, xiii, page 39. This is evidently No. 16 of the section given at pages 280, 281, of vol- 

 ume ii of the Final Report. 



Meg. A medium-grained, red sandstone. 



Mic. The section shows well rounded quartz grains in a rather abundant 

 cement of calcite and red iron oxide. 

 One section. 

 Age. Near the bottom of the St. Peter sandstone. u. s. G. 



No. 838. QUARTZYTE. (Red.) 



Redstone, near New Ulm. 



Ref. Annual Report, xiii, page 39. 



Meg. A rock of rather fine grain and brick-red color. Numerous quartz grains 

 occur embedded in a copious red, very fine-grained cement. 



Mir. There are rounded and sub-rounded quartz grains and some clouded, 

 altered feldspars in a matrix which is abundant and is composed of fine flakes of 

 micaceous material. These flakes appear to be both Muscovite and kaolinite. The 

 quartz grains are surrounded by a narrow rim of red iron oxide, and in the matrix are 

 also areas outlined by iron oxide, thus suggesting that some part of that which now 

 seems to act as the matrix of the rock was originally feldspar grains. One section. 



Age. Potsdam. u. s. G. 



No. 839. GRANITE (with augite). 



Sauk Rapids. 



Ref. Annual Report, xiii, page 39. Same as Museum No. 4466 (Annual Report, x, page 167). 



Meg. A medium-grained gray granite, composed of white to flesh-colored 

 feldspar, quartz, hornblende and biotite. 



Mic. The section shows a granitic aggregate, composed essentially of feldspar, 

 i I IK n't z, hornblende and biotite. The feldspar is more or less clouded and consists of 

 orthoclase and a minutely twinned plagioclase. The hornblende is green and seems 

 to be, in part, if not in whole, derived from augite. In the centers of some of the 

 hornblendes a little augite still remains. Magnetite, brown sphene, which is pleochroic, 

 and apatite are also present. One section. 



Age. Archean. u. s. G. 



