580 THE GEOLOGY OP MINNESOTA. 



[Greenwacke. Quartz and chlorite. 



No. 868A. GREENWACKE. 



From the same rock as No. 868, continuous with it; a rhomboidal mass showing a more rough and granular 

 weathered surface. 



Kef. Annual Report, xv, pages 246, 268, 387; Bulletin vi, pages 25, 41-43, 421, plate V, figure 6. 



. Gray, rough, sheared rock, the weathered surface being roughened by 

 projecting feldspar and quartz. 



Mic. This rock is hardly distinguishable from No. 868. Its greatest difference 

 consists in the more evident forms of old feldspathic grains which speck the surfaces. 

 There is no structure visible that proves the rock to have been originally plutonic or 

 effusive, though there is no question that the materials had an eruptive origin. 

 Zoisite is abundant, especially in the fragmental grains of feldspar. Some of the 

 green coloring matter is hornblende, and there are a few grains of epidotc. 



Two sections. N. H. w. 



No. 868B. GREENWACKE. 



" Shows the gneissic structure sometimes seen in No. 868; same locality." 

 Ref. Annual Report, xv, pages 246, 268, 387; Bulletin vi, pages 43, 421. 



. Similar to Nos. 868 and 868 A. 

 Mic. The section is similar to No. 868A, but is more markedly schistose and 

 the feldspars are more altered. 

 One section. 



Age. Keewatin. u. s. G. 



No. 868C. QUARTZ AND CHLORITE. 



"Quartz from a vein, inclosing green chlorite and having a schistose structure; same exposed surface." 

 Ref. Annual Report, xv, pages 246, 268, 387; Bulletin vi, pages 43, 421. 



Meg. A mass of coarse, white, vein quartz and fine-grained, schistose greenstone. 

 Mic. The section was made from the greenstone. It is markedly schistose and 

 is composed essentially of chlorite. 

 One section. 



Age. Keewatin. u. s, G. 



No. 868D. CHLORITE. 



"Contains a piece of chlorite from a fissure and a grain resembling a changed crystal of feldspar; same 

 locality." 



Ref. Annual Report, xv, pages 246, 268, 387; Bulletin vi, pages 43, 421. 



Meg. Chlorite, similar to the chlorite of No. 868C. The supposed feldspar 



crystal is considerably altered, soft, and of a greenish-gray color. No section. 

 Age. Keewatin. u. s. G. 



No. 868E. GREENWACKE. 



Same rock surface as No. 868; most usual and typical form of No. 868; near the west end of the small ridge. 

 Ref. Annual Report, xv, pages 246, 387; Bulletin vi, pages 43, 421. 



