9l4 THE GEOLOGY OF MINNESOTA. 



[Graywacke. Sericite schist. Granite. 



ROCKS COLLECTED BY H. V. WINCHELL. 



No. 2H. GRAYWACKE. (Sheared, or sericitic schist: fine.) 



Stuntz island, sec. 21, T. G2-15. 



Ref. Annual Report, xv, pages 276, 280, 283, 304, 310, 312, 3H, 413. 



Meg. Schistose indistinctly, also presenting a basaltic appearance. 



Mic. The rock is mostly a sericitic schist. The very fine micro-gran ulitic 

 groundmass having mica and much calcite, contains numerous forms of old feld- 

 spars that are much altered by the generation of secondary minerals, such as mica 

 and calcite. The points of darkening, on rotation between the nicols, are distinct, 

 but the twinning bauds are lost. In some places also no trace of the original feld- 

 spar is left, except its shape and size outlined in an area that has a general uniform 

 fineness contrasted with the surrounding variations. A little epidote and leucoxene 

 appear, the former in the areas of the altered feldspars. The feldspars show no new 

 growths of feldspar. One section. 



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



No. 2aH. SERICITE SCHIST. 



Pebbles contained in No. 2H. 



Ref. Annual Report, xxv, page 276. 



Meg. Soft and greenish, schistose. 



Mic. The rock consists entirely of very fine sericitic scales, and debris of feld- 

 spathic character, having a marked schistose structure. N. H. w. 



No. 4H. GRAYWACKE. 



Prom the island crossed by the line between sees. 15 and 16, T. 62-16, Vermilion lake. 

 Ref. Annual Report, xv, pages 281, 413. 



Meg. Gray, sericitic, hard, tough, compact, with pyrite. 



Mic. Quartz and old feldspars lie loosely in a micro-granulitic groundmass. The 

 latter are plainly striated, but still are very much replaced by secondary writ'lte and 

 calcifc. They, as well as the quartz, are interlocked at their margins, with the fine 

 groundmass. One section. 



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



No. 6H. GRANITE. (Homblendic.J 



North side of the bay in S. E. % sec. 7, T. 62-16, Vermilion lake. 

 Kef. Annual Report, sv, pages 282, 414. 



.]/>//. Reddish gray, somewhat gneissic. 



