PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 895 



Granite.] 



structure to pervade the rock. None of the mineral grains show any evidence of a 

 clastic origin. The quartz is clear and limpid and is in larger grains than the other 

 minerals; it makes up about half of the rock. The feldspar, while cloudy in small 

 areas, is usually clear; most of it is orthoclase, but some good-sized plagioclases are 

 present. The biotite is brown and fresh; it, more than any of the other minerals, is 

 chiefly confined to certain irregular lines. The biotite is in small scales, most all of 

 which are arranged with their long axes in the direction of the schistosity of the 

 rock. Hornblende of the ordinary green variety is present in a few irregular areas; 

 it appears very fresh. All the minerals of the rock present a decidedly fresh and 

 unaltered appearance. One section. 



Age. Archean (Keewatin). u. s. G. 



No. 521G. GRANITE. 



North shore of Snowbank lake where the east line of sec. 24, T. 64-9 W., cuts the shore. 

 Kef. Annual Report, sx, pages 60, 103 : Annual Report, xxii, page 156. 



Meg. A very fine-grained, dark-gray granite. 



Mic. Dr. A. H. Elftman's description of this section is as follows (Twenty- 

 second Annual Report, page 156): "Specimen No. 521G, from the S. E. J of N. E. 

 \ sec. 24, T. 64-9, is a fine dark hornblende granite. Under the microscope this 

 shows the feldspars, hornblende, sphene and magnetite. The hornblende has altered to 

 chlorite and shows no traces of augite." One section. 



Age. Archean. u. s. G. 



No. 522G. GRANITE. (Augitic. ) 







Small island in Snowbank lake, N. E. % S. W. % sec. 19, T. 64-8 W. 

 Ref. Annual Report, xx, pages 66, 103 ; Annual Report, xxii, page 156. 



Meg. A medium-grained, pinkish-gray granite. 



Mic. Dr. A. H. Elftman's description of this rock is as follows (Twenty-second 

 Annual Report, page 156) : " No. 522G , from the island in the N. E. J S. W. \ sec. 

 19, T. 64-8, is an augite granite. The mineral constituents are the same as in No. 

 271E.* Augite and hornblende are present in separate plates. There is no direct 

 alteration of the former into the latter, but the hornblende possesses the fibrous 

 cleavage of uralite and is a paramorph after the augite. Biotite is secondary from 

 the hornblende. In this section we have a change of augite to hornblende, which in 

 turn is altering to biotite and chlorite.'' Two sections. 



Age. Archean. u. s. G. 



*The description of No. 271E is as follows ( T >,: hi second A n n>ml Rt'i>fl, p. 155) : "On the west side of the narrow bay 

 in the W. % of sec. 20, T. 64-8, is a large outcrop of a light-gray granite :>To. 271EI. The ruck is medium grained, and the ferro- 

 magnesian minerals constitute about one-half of the rock mass. Under the microscoite this rock is shown to be an augite granite. 

 Orthoclttsi , inii'rni'Uni- and iillym-hisi' occur in equal proportions. All of the feldspars have a well-defined, clear zone around a 

 kaolini/ed centre and are in some cases porphyritically developed. Quartz is not very abundant and occurs in small grains. 

 The augite and hornblende are closely associated. The nn/iiii is of a light-green color, has no pleochroism and extinguishes from 

 45 to 50. It forms the cores of the hornblende, which has a darker color, is pleochroic in brown and dark green, and extinguishes 

 at less than 22. The cleavage of the hornblende is a continuation of that in the augite core. The line of division between the two 

 minerals is distinct, and the extinction angle of both minerals is readily measured along the same eleavagc. One pyroxene plate is 

 unaltered, and its extinction and striations bring it near to diallage. Hornblende occurs in several places in bent bundles of 

 slender rods. ,S'/*/ir/jc occurs in double wedges and rounded grains. M't'/ni-ti'i' anil t<i<.litr are secondary and are not abundant.'' 



