930 THE GEOLOGY OF MINNESOTA. 



[Greenstone. Hornblende schist. 



noted in No. 39S, but the stellate structure is wanting. Further, in the midst of this 

 actinolitic product are areas of loose magnetite and occasionally of irregular siderite 

 with a few small grains of quartz. Indeed, it appears that quartz and siderite 

 alternate in areas, forming the supporting background for this yellowish actinolitic 

 product. In a second slide the forms of the primordial pellets are distinctly preserved, 

 but they are replaced by the products of alteration, sometimes by siderite, which 

 frequently is of a single crystal orientation occupying nearly the whole area of the 

 original pellet, sometimes by a biotitic and ferruginous substance, and sometimes 

 by a globular or an interlocking quartz h'ner than the rest of the rock, but usually 

 they are in some part still preserved as greensand, often with shrinkage cracks. 

 These pellets are surrounded by an interlocking quartz. In still another section the 

 same characters are seen as in the last. Three sections. 



Age. Animikie. N. H. w. 



No. 55S. GREENSTONE. ("Mottled.") 



N. W. M s - w - M sec - 34 - T - 59-16, Mesabi Iron range. 

 Ref. Annual Report, xxii, page 128. 



Meg. Greenstone. 



Mic. Feldspar of a triclinic species composes this rock essentially, but there 

 was originally a ferro-magnesian mineral in small amount which is now turned to 

 chlorite. Some opaque leucoxene, some sphene, calcite and epidote are subsidiary in 

 amount. The structure seems to indicate that this rock has suffered pressure 

 amounting almost to crushing, but the feldspars are not lost as to crystalline form, 

 showing occasionally an interlocked growth. They have been subsequently rece- 

 mented and regenerated by a microperthitic deposition of a fresh feldspar. The rock 

 may have been a hornblende granite or a diabase with little augite. One section. 



Age. Keewatin. N. H. w. 



No. 58S. HORNBLENDE SCHIST. 



About 200 paces north of No. 57S. 

 Ref. Annual Report, xxii, page 128. 



Mey. Hornblendic. 



Mic. Hornblende and secondary interlocking glassy feldspars with a little biotite 

 compose this rock. One section. 



Age. Keewatin, recrystallized. N. H. w. 



No. 59S. HORNBLENDE SCHIST. 



Same locality as No. 58S. 



Ref. Annual Report, xxii, page 128. 



Meg. Hornblendic. 



Mic. Same kind of rock as No. 58S, but containing evidently also a considerable 

 quartz in the interlocking groundmass. One section. 



Age. Keewatin, recrystallized. N. H. w. 



