PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 635 



Granite. Mica schist. Gneiss.] 



cleavages, but its polarization colors. Mixed with the hornblende is a considerable 

 amount of a highly refractive and highly doubly refractive mineral, in fine detached 

 grains which are sometimes grouped round black, opaque particles as centres, which 

 are probably epidote. A few black, metallic particles are surrounded by a hematitic 

 stain. One section. 



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



No. 1027. GRANITE. 



From an island in the lake, in sec. 1, T. G4-11, cut by an apparent dike of mica schist. Bassimenan lake. 

 Ref. Annual Report, xv, pages 357, 358, 394. 



Meg. A fine-grained, pinkish, granitic rock. 



Mic. Quartz constitutes most of this rock, but it also has microcline and andeshic- 

 oliyoclase, the latter shown by an extinction angle of 72 on the bisectrix n p . The 

 feldspar is sometimes clouded by a gray substance, which gives it the appearance of 

 the sub-opaque leucoxene, whose nature is unknown, but which may be of the nature 

 of kaolin. These, with a little hornblende are the essentials of this rock. The large 

 microcline crystals sometimes embrace poikilitically both quartz and andesine- 

 oligoclase. One section. 



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



No. 1028. MICA SCHIST. 



Same locality as No. 1027. 



Ref. Annual Report, xv, pages 358, 394. 



Meg. A fine-grained, micaceous (biotitic) schist with hornblende and apparently 

 quartz and feldspar. The hand sample is crossed by a vein, one-fourth to one-half 

 inch wide, of pegmatyte which is composed mainly of pink feldspar. No section. 



Age. Archean. u. s. G. 



No. 1029. GNEISS. 



Same locality as No. 1027. 



Ref. Annual Report, xv, pages 358, 394. 



Meg. A medium-grained, dark-colored rock, gneissic in structure, composed of 

 biotite, hornblende, pinkish feldspar and quartz. No section. 



Age. Archean. u. s. G. 



No. 1030. GRANITE. 



From the same place as No. 1027, at three feet from the left of the contact on No. 1028. 

 Ref. Annual Report, xv, pages 358, 394. 



Meg. A fine-grained, flesh-colored, granitic rock. 



Mic. Essentially the same rock as No. 1027, but finer grained and having more 

 hornblende. There are also small amounts of biotite and of sphene, as well as of 

 pyrite. One section. 



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



