PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 871 



Greenstone. Granite.] 



unquestionable pebbly forms of different kinds of rock. This, however, all appears 

 to belong to the Upper Keewatin, and may be said to repeat the phenomena of Keke- 

 quabic lake on a small scale." This structure may be compared with the jointed gray- 

 wacke seen in figure 2, plate Y in vol. iv, and as a rock it is like the porphyritic 

 conglomerate, or porphyrel, of Zeta lake (vol. iv, page 281), except that the recrys- 

 tallization has proceeded farther than in the Zeta Lake porphyrel, and the rock has 

 been forced to occupy fissures in the elastics in the manner of an intrusive. N. H. w. 



No. 2247. GREENSTONE. (Igneous.) 



On the town line, north side of sec. 5, T. 63-9, not far from the lake. 

 Ref. Annual Report, xxiv, page 77. 



Meg. A gabbroid rock in which apparently pyroxene and magnetite exist, the 

 latter being reddish, and perhaps rutile or some other titanium mineral. Has a sharp 

 contact on a schistose and conglomeratic greenstone containing jaspilyte in indig- 

 enous masses. It differs from the greenstone containing the jaspilyte in that the 

 hornblendes (or pyroxenes) produce the prominent roughness, the feldspathic ingre- 

 dient occupying the depressions on the weathered surface, while in the prevalent 

 greenstone, which here embraces the jaspilyte, the surface roughness is produced by 

 a white siliceous net work which permeates the rock and stands out on weathered 

 surfaces. 



Mic. The feldspars, now much altered, still retain their ophitic relation to the 

 surrounding dark mineral, which, now uralite, was originally augite. With consid- 

 erable epidote in small isolated grains is also isotropic chlorite and semi-transparent, 

 highly refractive leucoxene, which in reflected light coming from the upper surface 

 of the slide appears dull white. Three sections. 



Age. Igneous greenstone of the Lower Keewatin. N. H. w. 



No. 2248. GRANITE. (Sub-porphyriMc.) 



On the town line, north side of sec. 5, T. 63-9, not far from the west end of the lake (which is near the 

 section line running north into the next town). 

 Ref. Annual Report, xxiv, page 77. 



Sub-porphyritic granite. This acts at first like an intrusive, but rapidly 

 widens out in the schistose greenstone. This specimen came from ten feet from 

 either side, weathers nearly white; has pyrite cubes. 



Mic. Quartz is quite common. It surrounds muscovite scales and interlocks 

 with itself and all the other minerals. It was hence the latest of the constituents to 

 take its place. It bears the same relation toward calcite, which is abundant. The' 

 rock contains a little sphene, pyrite, chlorite, and two feldspars, one of which appears 

 to be orthoclase. The feldspars which give the rock a sub-porphyritic aspect are 

 occasionally of the soda-lime series and embrace the muscovite scales in the same 

 manner as the quartz. One section. 



