630 THE GEOLOGY OP MINNESOTA. 



[Quartz schist. Quartz. Greenwacke. Greenstone. 



No. 1012. QUARTZ SCHIST. (Magnetic.. ) 



From boulders, which are angular, evidently from the rock near. Top of hill S. E. } sec. 19, T. 63-11, 

 south of Fall lake. 



Ref. Annual Report, xv, pages 324, 393. Compare Nos. 2111, 2112. 



Meg. Black, banded, magnetic, fine grained. 



Mic. In the quartz, which composes the most of the rock, is a powder of magnetite. 

 The latter is in grains of ultra- microscopic size, which by aggregation form larger 

 masses of irregular shape. The quartz is pierced also by the same spicules as 

 mentioned under No. 1000, supposed to be gnincriie from its twinning and its high 

 double refraction. 



Age. Archean (Lower Keewatin). N. H. w. 



No. 1013. QUARTZ. (Chalcedonic. ) 



From a vein in quartz schist, top of the hill, S. E. 1^ sec. 19, T. 63-11. 



Ref. Annual Report, xv, pages 245, 393; Annual Report, xviii, page 11; Annual Report, xxii, page 6; 

 Bulletin vi, page 69. 



Meg. Apparently the same kind of fine granular quartz as that of the quartz 

 schist, frequently called "chalcedonic quartz," but incorrectly, because the quartz has 

 not the fibrous structure characteristic of chalcedony, nor its negative, optical 

 character. 



Mic. The quartz is wholly recrystallized, whatever its original condition, in 

 interlocking grains which vary in size, being coarser along the centre of the vein. 

 Along the edges of the vein the quartz grains have about the same size as in the rock 

 in general. One section. 



Age. Archean (Lower Keewatin). N. H. w. 



No. 1014. GREENWACKE. 



Just south of the section line between sections 19 and 30, west of the trail; T. 63-11, south of Fall lake. 

 Ref. Annual Report, xv, pages 324-326, 393. 



Meg. An indefinite green rock or graywacke. 



Mic. There is much chlorite, hornblende, calcite and leucoxene, also considerable 

 quartz in scattered small grains of secondary origin, in this rock. There are forms 

 of some original feldspars, indicated by the greater transparency in areas, which are 

 crowded with calcite and other impurities, but the distribution of the elements is so 

 promiscuous that no ophitic structure is discernible. 



Age. Archean (Lower Keewatin). N. H. w. 



No. 1015. GREENSTONE. 



N. E. % sec. 30, T. 63-11; south of Fall lake, near Garden lake. 

 Ref. Annual Report, xv, pages 325, 394. 



Meg. Appearing like a fine, brecciated graywacke, rough and angular in general 

 outward aspect. 



