1014 THE GEOLOGY OP MINNESOTA. 



PLATE IV. 



Page. 



FIGUKE 1 Three polygonal or basaltic masses of taconitic hematite, formed by the 

 shrinkage of volcanic ash, Prairie River falls. Rock No. 1527, natural 

 size ' 738 and 991 



PIG. 2 Diabase, showing a glomero-porphyritic aggregation of the labradoritcs. 

 supposed to illustrate the manner of segregation of anorthosyte masses 

 from diabase. Rock No. 2051, natural size 830 



