PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 515 



Granite. Amphibolyte.] 



mineral, which was probably hornblende, is completely replaced by chlorite, (<!/<;/< 

 and a little epidote. 



One section examined. 



Aye. Archean, probably of date between the Lower and Upper Keewatin. 



No. 730. GRANITE (with chlorite). 



From the rapids between West Sea Gull and Sea Gull lakes. Near the centre of N. E. J4 sec. 9, T. 65 5 \V. 

 Kef. Annual Report, x, pages 88, 89. 



Meg. Similar to No. 729, but with more quartz. . 



MIC. The section is similar to the last two (Nos. 728 and 729), and orthoclase 

 and plagioclase are both present. The original ferromagnesian constituent, which, 

 judging from areas with outlines of hornblende cross sections, was hornblende, is 

 altered to chlorite and calcitc with some epidote. The chlorite is not as green nor as 

 abundant as in No. 729. 



One section examined. 



Age. Archean, probably of date between the Lower and Upper Keewatin. 



Remark. These three samples (Nos. 728, 729 and 730) are good representatives 

 of the mass of the Saganaga granite, which is a coarse-grained hornblende granite. 



An analysis* of a characteristic specimen of the Saganaga granite No. 686G from Saganaga lake (S. 



W. % N. E. % sec. 22, T. 66-5 W.) is as follows: 



SiO 2 69.34 



A1 2 O S 17.2f> 



Fe 2 O 3 and PeO 2.46 



CaO 3.43 



MgO 1.18 



K 2 '.71 



Na 2 O 4 A3 



H,O 1.17 



Total 99.87 



This- shows that the amount of K,0 is quite small, and the rock is thus more 

 properly called a quartz dioryte, or perhaps a soda granite, for it is evidently from 

 the alteration products- of the hornblende that a large amount of the lime is 

 contained in this mineral, thus leaving a smaller amount than would be thought 

 from the analysis alone, of the anorthite molecule in the feldspar. u. s. G. 



No. 731. AMPHTBOT.YTE. 



South side of West Sea Gull lake, near the stream which flows from Prog Rock lake. Near the centre of 

 the N. % sec. 17, T. 65-5 W. 



Ref. Annual Report, x, pages 88-90, 93-96. 



A fine-grained, greenish-gray rock, rather soft, and having a few veinlets 

 in which is some calcite. The samples are quite small and do not show any marked 

 schistosity. 



*M;ule by Mr. A. D. Mi-ils, gas inspector of Minneapolis. Tii'rnty-flnt Ami mil Report, p. 43. 



