PETROGRAPHY OF THE KEWEENAWAN 



657 



Keweenawan, and no such case has been noted in Minnesota. Slight 

 peculiarities were not rare; as, for example, the gneissic appearance, 

 mentioned by Professor Hall regarding a Pine City exposure. This 

 was prominent in the lower twenty-five feet of a thick hackly flow.^ 



In Michigan some diabase dikes in rocks near the lavas have been 

 compared with the lavas, as an indication of their relationship. A 

 similar comparison may be instituted here for Minnesota, and 

 extended to include other occurrences of basic rocks in the central 

 and northeastern part of the state. Earlier analyses reported by 

 Streng, Winchell, and Irving are included in the tabular comparison, 

 but analyses are not quoted. 



TABLE X 

 Chemical Classification by Locality and Form 



TABLE XI 



Types of Diabase Chemically Classified 



I C. W. Hall, Bm//. Geol. Soc. Am., XII, 313. 



