722 THE GEOLOGY OF MINNESOTA. 



[Gneiss. Greenwacke. 



No. 1416. GNEISS. 



Same locality as No. 1414. 



Ref. Annual Report, xvi, pages 103, 1CM, 1i~>. 



MCIJ. Reddish, porphyritic; intended to show the intergrading of the gneissic. 

 the porphyritic and the conglomeritic characters of this rock. 



Nic. The rock is mostly composed of ragged feldspars which are zoned, twinned, 

 replaced by micro-granular new growths and reconstructed by secondary feldspathic 

 material. The rock, therefore, is quite compact and firm. Hornblende, more or less 

 changed to chlorite, conies next in amount. This runs in irregular, spreading streaks 

 and strings, somewhat as in a schist, but not in a schistose uniformity of direction. 

 It is accompanied by magnetite and by actinolite. Epidoteis in scattered fine particles 

 and calcite is quite common. Throughout the whole, and generally between and 

 around the feldspars is more or less of the common micro-granulitic mosaic of 

 t/Ktirtz and feldspar. This varies in fineness. In some areas this structure alone 

 fills the slide, and spreads in a band which runs with more or less distinctness from 

 one side of the slide nearly to the other. This fine mesh is evidently due to a secon- 

 dary development of later date than the deposit of the feldspars in the places they 

 occupy, and indicates that a fine debris, largely feldspathic, has been entirely worked 

 over and given this new crystalline condition, a structure, however, which did not 

 much change the forms of the larger old feldspars. One section. 



Aye. Archean (modified Upper Keewatin). N. H. \v. 



No. 1417. GNEISS. 



Shingwak island, north of Animikie island, Kekequabic lake. 

 Ref. Annual Report, xvi, pages 105, 125. 



Meg. Rock appearing like No. 1416. 



Mic. The description No. 1416 will apply to this rock. One section. 

 Age. Archean. N. H. w. 



No. 1418. GNEISS. 



Same island. 



Ref. Annual Report, xvi, pages 105, l'J.~i. 



Meg. The red crystals are in bands that alternate with others of a greenish 

 biotitic rock. 



Mic. Similar to No. 1417, except that the larger feldspars are more obscured 

 and replaced by secondary, often micro-granulitic structure. One section. 



Ayr. Archean. N. H. w. 



No. 1419. GREENWACKE. (Pfbbl.ii tuff.) 



From a very small island directly south of Shingwak island. 

 Ref. Annual Report, xvi, pages 105, 125. 



Meg. Fine grained, greenish. 



