PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 873 



Dioryte. Qabbro. Diabase.] 



No. 2252. DIORYTE. (Uralitic.) 



Near the lake mentioned, and on the knob presenting a northeastward vertical cliff mentioned under No. 

 2251. S. W. M sec. 33, T. 64-9. 



Ref. Annual Report, xxiv, page 78. 



Meg. Has the aspect of an igneous greenstone of medium grain; occurs as an 

 irregular intrusive in the midst of the general greenstone. 



Hie. The relation subsisting between the hornblende and the altered feldspars 

 is imperfectly that of an ophitic rock, showing that this rock was one that congealed 

 from fusion, and is of later date than the greenstone which it cuts irregularly. One 

 section. 



Age. An ancient greenstone cutting Lower Keewatin greenstone. N. H. w. 



No. 2253. GABBRO (ivith quartz). 



Same place as No. 2252, 



Ref. Annual Report, xxiv, page 78. 



Meg. Sprawling, dike-like areas, nearly white, in rock No. 2252. 



Mic. Quartz is quite abundant in this rock, but it plainly was last to take its 

 place amongst the other minerals. The feldspar is labradorite, as shown by its acute 

 bisectrix n g , and its extinction angle at about 20 on a section cut perpendicular 

 to n t . The augite is scarce and is broken and uralitized, but not wholly lost. One 

 grain shows an angle n t .:c of 54, which indicates an cegyrine-augite. These augites 

 are idiomorphic toward the labradorite, as well as toward the quartz. One section. 



Age. Gabbro cutting Lower Keewatin greenstone. 



Remark. Owing to its light color, and the evident quartz, this rock was taken 

 in the field to be granitic. The augite is inconspicuous and on alteration has lost its 

 usual dark color, becoming light yellowish green, and the resultant uralitic mineral 

 is scarcely pleochroic. A little original magnetite was apparently titaniferous, as it 

 appears now as a dark Icttcoxene with a white reflecting surface. N. H. w. 



No. 2254. DIABASE. (Uralitized.) 



At the west end of another small lake, a little further north, yet in S. W. % sec. 33, T. 64-9. 

 Ref. Annual Report, xxiv, page 78. 



Meg. A greenstone, cutting a coarse Keewatin conglomerate; fine grained at 

 the conglomerate contact. 



Mic. This rock was originally ophitic. It now has no augite, but uralite; also 

 leucoxene, calcite and epidotc. Two sections. 



Aye. Dike in Upper Keewatin. N. H. w. 



No. 2255. DIABASE. (Uralitized.) 



North side of the west end of the same lake ; top of the southward facing cliff. 

 Ref. Annual Report, xxiv, page 79. 



