PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 353 



Dioryte. Granite.] 



Mic. The section shows quartz abundant, and a feldspar which is in part 

 microcline, and in part perhaps orthoclase or oligodase, but which is rather too much 

 kaolinized to warrant an attempt at specific determination. One section. 



Age. Archean (near transition to Coutchiching). 



Remark. Where No. 402 occurs in large masses its boundary is not always 

 parallel with the schists, but jogs across a foot or two of them and then runs again 

 parallel, sometimes also crowding them confusedly. This is on the island nearest 

 the point at the narrow passage for canoes bound west. The extremity of the point 

 is of the same character of rock, but the change from the finer grained chloritic to 

 mica slate or schist, is very gradual and imperceptible, the colors and characters 

 blending and mixing apparently in the same rock. N. H. w. 



No. 403. DIORYTE. 



Vermilion lake; same place as No. 401. 



Ref. Annual Report, ix, pages 99, 101; Bulletin ii, pages 120, 121. 



Meg. A dark-gray, rather fine-grained, apparently micaceous and hornblendic 

 rock. 



Mic. The most conspicuous mineral, and perhaps the most abundant, is a 

 pleochroic hornblende, which has elongated sections, but rarely shows good cleavages. 

 Next to this is epidote, scattered irregularly throughout. Feldspar is both original 

 and secondary, the former filled with micaceous microliths and having ill-defined 

 boundaries, and the latter being clear and quartz-like in extinctions, frequently with- 

 out cleavages or twinning. This feldspar is not common in this slide. When albite 

 twinning appears it has the aspect of the species albite, as described in the rock No. 

 872. Chlorite is hardly distinguishable from some of the hornblende. When 

 fortunately a grain is destitute of cleavage, remains dark or nearly dark on rotation, 

 and has a rounded or perhaps a somewhat angular-hexagonal outline, it may be tested 

 in convergent light. If it give a dark cross, or a very low angle 2 E, it is plainly 

 chlorite. Apatite is present in a few stout, highly refractive crystals, evidently from 

 the original crystallization from a molten magma. Sphene is scarce, and biotite 

 common. Pi/rite shows a few cubic sections. Two sections. 



Age. Archean. 



Remark. As remarked by Wadsworth this rock is probably an old eruptive. 

 The glassy feldspar has much the appearance of quartz, which latter we do not find 

 in the slide. It may be compared with rock Nos. 380, 875 and 872. N. H. w. 



No. 404. GRANITE (with biotite). 



Vermilion lake, on the north shore; perhaps in sec. 26, T. 63-17 W. 

 Ref. Annual Report, ix, pages 99, 100. 



Meg. A fine-grained gray granite, composed of gray to pinkish feldspar, quartz 

 and biotite. 



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