PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 685 



Granite. Feldspar schist.] 



Remark. If this were originally a basic intrusive rock, and were then sheared 

 and altered by such action, it would perhaps have produced a rock like this. If it 

 had been a coarse debris from basic rocks, produced by erosion, such as some parts 

 of the Ogishke conglomerate, and had been sheared in the same way, it would prob- 

 ably also have produced such a rock. The diopside shows distinct cleavages parallel 

 and perpendicular to the optic plain in a section perpendicular to an optic axis, being 

 therefore the pinacoidal cleavages rather than the prismatic. N. H. w. 



No. 1301. GRANITE. 



At a point about a mile north of Gunflint lake, on the same town Hue. 



Meg. An imperfect granite or gneiss. 



Mi<: The foregoing description of No. 1300 would also apply to this rock, only 

 requiring less hornblende and more quartz. One section. 



Age. Archean. N. H. w. 



No. 1304. FELDSPAR SCHIST. (Micaceous.) 







North from Gunflint lake, at the " black belt." 

 Ref. Annual Report, xvi, pages 70, 120. 



Meg. Shows a blending of the characters of the mica schist and those of the 

 regenerated porphyritic schist (porphyrel). 



Making a closer inspection of the rocks of the Vermilion group (t. e., the Coutchiching of Lawson) at this 

 point, they are found to extend north and south about fifteen rods. There is certainly a conformable transition 

 from the Keewatin to this, which is chiefly mica schist, at least superficially. At some depth within the rock 

 perhaps there would be found a greater proportion of hornblende, since it seems that the mica results from the 

 natural decay of the hornblende The interbedded, light-colored rock is the gray "porphyritic" rock of the lake 

 shore, but has some mica scales. It acts here much like the so called "dikes" of gneiss that are interstratified 

 with the Vermilion group or mica schists north of Vermilion lake. It fades out by very slow transitions into the 

 mica schist, and it also is replaced abruptly by it. It runs to needle-shaped points and vanishes conformably 

 in the darker rock. If it is, hence, eruptive, then this porphyritic rock everywhere is eruptive, and also the 

 schist into which it graduates at the lake shore. Rock No. 1304 shows a blending of the characters of the mica 

 schist with those of the rock that shows the porphyritic characters. The belt from which this came is about 

 ten inches wide, and such are numerous in the schists. Indeed, there can be seen almost eYery kind of transi- 

 tion and every direction of gradation between the schist, the hornblendic rock and the porphyritic and gneissic 

 rock. They all occur as strings and as isolated portions in each of the others. There are belts of coarsely horii- 

 blendic rock that alternate several times in the mica schist, conformably with the strike, but the former are 

 confused, lumpy and uncertain. They may have been basic eruptives in the sediments of the Keewatin at the 

 time of their accumulation, and so spread out as sheets approximately conformable to the sediments. 



The section foregoing was made on the town line extended north from the south side of the lake between 

 T. 65-1 and T. 65-2 W. 



Mic. Green ltont/>/e>t<te and a little biotite give color to the rock. There is much 

 secondary quartz and glassy feldspar and some larger feldspars that appear to be ortlto- 

 r/W. There are also much decayed feldspars, on one of which a determination by 

 extinction on n v in the acute angle of the optic plane indicates andesine-oligoclase. 

 The glassy feldspars generally show no cleavage nor twinning, and therefore it is 

 difficult to determine them specifically. It appears in some cases that an old feld- 

 spar furnished the nucleus on which the fresh feldspar grew. One section. 



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



