PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 341 



Dloryte. Porodyte.] 



lapping of the grains. In places the feldspar is in larger irregularly and indistinctly 

 outlined areas, and contains the other materials of the rock poikilitically. These 

 areas have undulatory extinction quite frequently. It is not improbable that quartz 

 is also present, although none was determined certainly. 



Age. Archean (Keewatin). 



Remarks. This rock differs from others just described in that the feldspar areas 

 are not so evidently the result of a fracturing of a larger grain. Here it does not 

 seem improbable that the larger feldspar areas are the result of recrystallization 

 in situ. u. s. G. 



No. 380. DIORYTE (vrith quartz). 



Vermilion lake; one mile southwest from the mouth of the stream from Mud lake; S. E. J N. W. J4 sec. 

 12, T. 62-15 W. 



Ref. Annual Report, ix, page 96; Annual Report, xv, page 306. This is the same rock as No. 875. Com- 

 pare No. 403. 



Meg. Massive, greenish-gray, medium-grained rock with some hornblende and 

 a triclinic feldspar. 



Mic. The section shows much dichroic, green hornblende, calcite, old feldspars 

 which are plainly a plagioclase and chlorite, with a little epidote and apatite. Some 

 of the feldspars are nearly lost in the products of their own decay, being charged 

 with micaceous scales and sometimes holding micropegmatitic quartz. Quartz also 

 exists as large isolated grains, and in one case an angular quartz is surrounded by a 

 gray mass that has distinct crystalline orientation and which is probably a feldspar. 

 This supposed feldspar, which is non-striated, also embraces two small hornblendes, 

 and some calcite, and may be of secondary origin. The hornblende is generally 

 idiom orphic toward the feldspar, as well as toward the calcite and the chlorite. 



One section. 



Age. Archean (Keewatin). 



Remark. This is a peculiar rock in that the hornblende, as well as some quartz, 

 antedated the feldspar and appear now as idiomorphic crystals surrounded by the 

 feldspar. It seems to be a changed basic eruptive of the dioryte family. In the slide 

 made from No. 875, the same features are visible, and further, it is apparent that the 

 feldspars had two periods of growth, since they are zoned. It is the earlier feldspar 

 generation that embraces the hornblende crystal mentioned above. Still another 

 interesting feature is apparent in the section of rock No. 875, viz.: a quartz crystal, 

 also embraced in a feldspar grain, has governed the orientation of pegmatitic quartz 

 which has entered the surrounding feldspar. N. H. w. 



No. 381. PORODYTE. 



Vermilion lake; probably near the north line of sec. 13, T. 62-15 W. 

 P,ef. Annual Report, ix, page 96; Bulletin ii, page 123. 



