GEOLOGY OF THE LONG LAKE QUADRANGLE 



507 



A slightly different, though yet more silicious rock is a quartz 

 gneiss from the small Grenville area lying between Long lake and 

 Pickwacket pond. It is a quartz, feldspar, phlogopite rock, with 

 zircon as the only observed accessory mineral. The feldspar is so 

 altered as to unfit the rock for chemical anabasis, but still admits of 

 accurate microscopic determination. Part of it is oligoclase, about 

 Abj Ani, and the remainder seems orthoclase, at least it is un- 

 twinned. With no analysis of the phlogopite available it is as- 

 sumed to have the composition of the phlogopite from Edwards, 

 N. Y.^ With these assumptions the microscopic analysis yields the 

 following result (2-H-1). 



Units measured Sp. Gr. 



Quartz 2060 x 2 . 65 



Feldspar ~ 326x2.64 



Phlogopite 198 X 2 . 85 



Zircon 3x4.5 



Total 2587 



Units 

 by weight 



% 



weight 



= 5459 = 





79-13 



= 861 = 





12.48 



= 564 = 





8.18 



= 14 = 



I 



. 2T 



6898 



00 .00 



SiO, . 



A1203 



FeO... 

 MgO . . 

 CaO... 

 Na^O . 

 K2O.. 

 Zr02. 



Qz. 



79 



Total I 79, 



Alb. 



Anor. 



Phlog. 



6.48 1.34 



1.80! I . 1 2 



i.oS 



0.66 



3 



91 







95 







03 



2 



52 







03 







74 



Zir. 



O.Q7 



o . 14 



9.36 3.12 



8.18 



Total 



90 



93 



3 



87 







03 



2 



52 







66 



I 



II 







74 







14 



TOO 



00 



It is quite possible that 20% or less of the feldspar is orthoclase, 

 which would affect the soda-potash ratio perceptibly and the silica- 

 alumina ratio slightly. The composition of the phlogopite may also 

 vary somewhat from that assumed, and is likely to in the iron con- 

 tent more especially. While these uncertainties considerably affect 

 the calculation when regarded as an exact rock analysis, they would 

 affect it in such slight manner, from the standpoint of the general 

 rock character, that it may be regarded as quite certain that we 

 are dealing with a metamorphosed sandstone, slightly aluminous 

 and slightly calcareous, but otherwise entirely normal. 



Associated with the quartz gneisses about Lake Catlin is a much 

 less quartzose rock which is quite micaceous. The thin section 



I Dana. Syst. Min. Ed. 6, p. 633, no. 8. 



