566 THE GEOLOGY OF MINNESOTA. 



[Granite. Epidosyte. Diabase. 



No. 840. GRANITE. (Hornblendic. ) 



East St. Cloud. 



Ref. Annual Report, xiii, page 39. Same as Museum No. 2128 (Annual Report, vii, page 51). 



Meg. Very similar to No. 839. 



Mic. The section, which is quite thick, shows a granite, composed of clouded 

 feldspar, quartz, green hornblende and Motile. One section. 



Age. Archean. . u. s. G. 



No. 841. GRANITE. (Hornbtendic. ) 



Near (north of) Motley. 



Ref. Annual Report, xiii, page 39. Same as Museum No. 2596. 



Meg. A medium-grained, gray granite, composed of quartz, greenish to pinkish 

 feldspar and hornblende. 



Mic. The section shows a granite, composed of much clouded feldspar, quartz 

 and hornblende. Some epidote and chlorite are also present. The sections are much 

 too thick for study. Two sections. 



Age. Archean. u. s. G. 



No. 842. EPIDOSYTE (?) 



Prom sections 17 and 18, Ashley, Stearns county. 



Ref. Annual Report, xiii, page 39. Same as Museum No. 4499 (Annual Report, x, page 168). 



Meg. A medium-grained, greenish, granitic rock, composed of feldspar and 

 epidote. 



Mic. The section shows a rock of rather coarse grain, composed essentially of 

 feldspar and epidote. The feldspar is in large allotriomorphic grains which some- 

 times show polysynthetic twinnings. The mineral is optically positive and a section 

 closely perpendicular to the acute bisectrix gave an extinction angle of 19 to 20. 

 A test with hydrofluosilicic acid showed the presence of a large amount of soda and 

 practically no potash and lime. The feldspar is thus albite. The epidote is yellow 

 and pleochroic; it exists in grains smaller than the feldspars, and frequently minute 

 grains occur in the feldspar. Two sections. 



Age. Archean. u. s. G. 



No. 843. DIABASE. 



From a dike in the Motley granite. 



Ref. Annual Report, xiii, page 39; Bulletin ii, page 116. Same as Museum No. 2593. 



Meg. A rather coarse-grained diabase. 



Mic. The section shows an ordinary diabase. The feldspar is plagioclase 

 (species not determined) and is in places considerably altered. The augite is largely 

 altered to hornblende, chlorite and dust-like material. Iron ore, probably ilmenite, is 

 present, and there is some secondary quartz. Two sections. 



Age. Dike cutting Archean rocks. u. s. G. 



