768 THE GEOLOGY OP MINNESOTA. 



[Granite. Dioryte. Quartzyte 



Remark. There is but little sign of metamorphism in this rock. It appears in 

 the main to be a debris of basic rock produced by erosion. Although it shows this 

 coarser grain in a direction toward the granite, that change is not attributable to the 

 advent of the granite, for the feldspars are all "old" feldspars. The hornblendes 

 show no secondary growths. This rock suggests some of the coarse green schists of 

 Kekequabic lake. N. H. w. 



No. 1722. GRANITE. 



Boot island, in the central part of Snowbank lake. 



Ref. Annual Report, xxi, page 156 ; Annual Report, xxii, page 157. 



Meg. Rather fine grained, but with large crystals of a feldspar. 

 Mic. The coarse feldspar crystals seem to be largely of microcline. They 

 enclose numerous smaller feldspars. One section. 



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



No. 1723. DIORYTE. (Camptonyte?) 



Near the same place as No. 1721. 

 Ref. Annual Report, xxi, page 156. 



Meg. A dike, from six inches to thirty-six inches wide, cutting through the 

 eastern continuation of No. 1721, which here becomes a coarse conglomerate, some- 

 what metamorphosed. 



Mic. In a fine groundmass consisting solely of feldspar and hornblende micro- 

 liths, the former tending indistinctly to a streamed structure (i. e., a diabasic 

 structure), are idiomorphic crystals of feldspar and hornblende. These later crystal- 

 lizations are slightly zoned. One section. 



Age. Archean (dyke). 



Remark. The structure of this rock is much like that of esterellyte, with the 

 exception that the flowage structure has not been noted in esterellyte in Minnesota. 

 In like manner it cuts a rock (No. 1721), which resembles the green schists of Keke- 

 quabic lake, which are cut by the esterellyte of that locality. These coincidences 

 are so striking that it is a reasonable inference to assume their equivalence of age, 

 and an alliance in origin. N. H. w. 



No. 1724. QUARTZYTE. (Gray r/rit. ) 



Shore of Snowbank lake, N. W. J^. sec. 35, T. 64-9. 

 Ref. Annual Report, xxi, page 156. 



Meg. Gray, fine-grained crystalline rock. It appears some like the Ogishke 

 conglomerate, and at the same time it is granitic, or granitized. There are areas 

 which show a true granitic structure with abundant orthoclase(?) crystals. This 

 rock and Nos. 1721 and 1723 are a part of the greenstone of this area. They some- 



