602 PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 



[Slate. Greenstone. Granite. 



Remark. From the field notes and the slide this rock may be regarded as a 

 quartz-porphyry which has been sheared, but this origin for the rock is not 

 absolutely certain, as a tuffaceous deposit or a recomposed quartz-porphyry might 

 take this form. Compare No. 913, which is a similar rock and seems to be clearly a 

 quartz-porphyry. u. s. G. 



No. 921. SLATE. (Black.) 



South shore of Pine island, Vermilion lake, at the west line of sec. 6, T. 62-15 W. 

 Ref. Annual Report, xv, pages 303, 389; Annual Report, xvii, pages 194, 215. 



Meg. A fine-grained, hard, black slate. 



Mic. The rock is very fine grained and is composed of quartz, probably also 

 feldspar, chlorite, muscovite, kaolinite, epidote and pyrite. There is also much dust-like, 

 black material. 



One section. 



Age. Keewatin. u. s. G. 



NO. 922. "GREENSTONE." 



South shore of Pine island, Vermilion lake; S. W. J sec. 1, T. 62-16 W. 

 Ref. Annual Report, xv, pages 303, 304, 389. 



Met/. A fine-grained, grayish-green rock, resembling some of the "greenstones" 

 of the Keewatin, Calcite is present in small seams. 



Mic. The -section shows a fine-grained rock, which is probably an altered, basic, 

 igneous rock, but its original species cannot be told. The constituent minerals form 

 a confused mass composed of zoisite, fibrous, almost colorless hornblende, epidote, 

 feldspar, muscovite, quartz and calcite, the minerals being named approximately in 

 the order of their abundance, the most abundant being named first. 



One section. 



Age. Keewatin. 



Remark. From the field notes one might judge that this specimen was part of 

 a "greenstone" dike. u. s. G. 



No. 923. GRANITE (in contact with biotite schist). 



Southwest corner of Avis island, Vermilion lake, near centre of sec. 35, T. 63-17 W. 

 Ref. Annual Report, xv, pages 291, 389. 



Mi'!/. The granite is of medium grain and light gray in color. It is composed 

 of feldspar, quartz and muscovite. The biotite schist is of medium grain for such a 

 rock and is dark gray in color. The contact between the two rocks is sharp and 

 distinct and runs about parallel with the cleavage of the schist. 



Mic. The granite is composed of grains which vary considerably in size and 

 which interlock irregularly. The rock seems to have suffered some granulation. 

 The essential minerals are quartz, feldspar and ni *<<>/ He, The quartz frequently 



