746 THE GEOLOGY OP MINNESOTA. 



[fineiss. Amphibolyte. Graywacke. 



No. 1573. GNEISS. 



North bay, on lake Nipissing, Ontario. 

 Ref. Annual Report, xviii, pages 50, 51, 62. 



Meg. Gray gneiss, fresh, quite siliceous, banded. 



- Mic. The section shows qmu'tz and glassy feldspars much resembling quartz, 



with a little biotite, apatite and sphene. The centres of the feldspars are sometimes, 



but not usually, occupied by a 1 mass of alteration products in a manner precisely like 



those noted in the "old feldspars" of the region of Kekequabic lake. One section. 



Aye. " Laurentian." 



Remark. This rock is a recrystallized sedimentary one, shown by its universal 

 coarsely banded structure, and the constant and parallel direction and width of the 

 bands. The existence of the central decayed cores in the feldspars can be referred 

 to the survival of remnants of older feldspars existing in the original elastics. 



N. H. w. 

 No. 1579. AMPHIBOLYTE. 



Stobie mine, Ontario. Prom the dump of the deep shaft which was abandoned. 

 Kef. Annual Report, xviii, pages 52, 62. 



Meg. Coarsely crystalline with hornblende. 



Mic. Two-thirds of the slide is composed of a large hornblende crystal. In the 

 rest of the slide is a mingling of small hornblendes, feldspar, sphene, magnetite, hintitc. 

 Sphene frequently surrounds the magnetite grains. One section. 



Age. ( ?) N. H. w. 



No. 1590. GRAYWACKE. 



Railroad crossing of Vermilion river, Ontario. 

 Ref. Annual Report, xviii, pages 54, 63. 



Meg. There are four specimens of this number. Three of them show a dark, 

 laminated, little slaty, fine-grained, gray wacke-like rock. The other is much coarser 

 grained, non-laminated and rough weathering; it has distinct grains of quartz. 



Mi<-. The section was made from the last mentioned specimen. Quartz and 

 feldspar grains make up the mass of the rock. These are sub-angular, angular and 

 sub-rounded. The quartz is more abundant than the feldspar, which appears to be 

 sometimes orthoclase, sometimes pluffiorlnnc, and rarely microcline. The feldspar is 

 frequently considerably altered and filled with dust-like black inclusions. This black 

 material, which is perhaps carbonaceous, is common throughout the slide, especially 

 between the grains of quartz and feldspar. There are some small flakes of chlorite 

 and also of a colorless to yellowish, brightly polarizing, micaceous mineral, though 

 not certainly muscovite. One section. 



Age. " Huronian," probably Lower Cambrian. u. s. G. 



