PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 345 



Quartz-porphyry.] 



No. 386. QUARTZ-PORPHYRY. (Altered.) 



"On a small island near the southeast shore; rock like No. 384. Here the schistose structure, sloping 

 southeast, runs S. 50 W. by compass, and is sometimes a little wavy." Vermilion lake; perhaps in the centre of 

 the W. }i sec. 22, T. 62-15 W. 



Ref. Annual Report, ix, page 97. 



Meg. A greenish gray, roughly schistose rock quite similar to No. 384, but 

 having almost no visible quartz. 



Mic. The section is similar to No. 384. The feldspar fragments are numerous 

 and very much decayed. Only a few quartz grains are present. One section. 



Age. Archean (Keewatin). u. s. G. 



No. 387. QUARTZ-PORPHYRY (?) ( Slieared. ) 



"About a mile southwest of the last the rock varies to a schistose, chloritic syenyte, of a light-gray color. 

 This is apparently only a variation in the ingredients of No. 386. It is a firm rock, and at a distance appears like 

 massive granite or syenyte; yet, along the lake shore, it parts in a gneissoid manner. It rises higher than the 

 adjacent hills, and is coarsely jointed, so that its rhomboidal parts rise like whitened sheep's backs. It extends 

 perhaps twenty rods." Vermilion lake; near the centre of S. % sec - 21, T. 62-15 W. 



Ref. Annual Report, ix, page 97. 



Meg. A gray rock, somewhat sheared and thickly studded with porphyritic 

 crystals of white feldspar. There are also less numerous and smaller, though 

 abundant, porphyritic crystals of quartz. The groundmass in which these crystals 

 are embedded, is sparse, aphanitic and dark gray. (See Nos. 874, 874 [A] and 1957.) 



Mic. The section shows a rock which has been stretched or sheared, and this 

 structure is shown both by the crushed and fissured larger grain and by yellowish 

 lines which run roughly parallel in the section. The rock is composed of crystals 

 and fragments si feldspar and quartz in a finer groundmass. The feldspar seems to 

 be in part orthoclase and in part a plagioclase, probably anorthoclase. It is altering to 

 wricite, and also in places contains minute crystals and grains of a colorless, strongly 

 refractive mineral with low double refraction which is thought to be zoisite. The 

 groundmass is of very fine grain, and is composed of quartz, feldspar, sericite, calcite 

 and acfiiiolite ( ?). Pyrite and also probably granular epidote are also present. 

 The mineral referred to questionably as actinolite is in fibres, is usually yellowish, 

 although sometimes colorless, and makes up most of the yellowish lines mentioned 

 above. It is usually not pleochroic, but sometimes shows slight pleochroism, varying 

 from colorless to straw yellow, the latter being the color of the ray which vibrates 

 parallel to the length of the fibres. It may be that this mineral is muscovite, 

 slightly colored, rather than actinolite, as the rough measurements made showed 

 practically parallel extinction. (Compare No. 431.) Two sections. 



Age. Keewatin. 



Remarks. This rock would be usually taken for a stretched quartz-porphyry, 

 and this is probably its nature. But the fact that in this immediate vicinity is the 



