PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 817 



Granite.] 



the rims interlock with their neighbors, but the old forms are seldom so thickly set 

 as to come into contact with each other. Some Motite, epidote, sphene and hornblende 

 are scattered through the slide, while quartz is abundant. One section. 



Age. Archean. N. H. w. 



No. 1992. GRANITE. 



Same place as No. 1991. 



lief. Annual Report, xxiv, page 2. 



Meg. Coarse, granitic or pegmatitic, vein-like rock, enclosing areas of No. 1991, 

 much lighter colored than No. 1991. 



Mic. The large feldspars have a micro-perthitic structure, the later feldspar having 

 insinuated itself along the cleavages and in other irregular fissures or points of weak- 

 ness. From this microscopic form the secondary growth spreads into larger patches, 

 and in several such it shows the microcline quadrillage. Microcline is also in independ- 

 ent larger grains. It thus appears that microcline forms a refilling for a semi-decayed 

 or crushed feldspar. Frequently thus an old feldspar, with ragged remnants, is filled 

 in and surrounded by a microcline border, about one-half of the area showing the quad- 

 rillage and the other not. Still it is not always plainly microcline which forms the 

 secondary ingrowths, but a fine, thread-like feldspar scattered in minute films which 

 become visible because of their different orientation. They extinguish simultaneously 

 and lie approximately parallel, in two series, one of which is in the direction of the 

 basal cleavage. The older crystal, in this case, is apparently andesine-oligoclase, having 

 an extinction of 3 on n e . The slide is entirely free from the colored bisilicates. The 

 quartz has been much fractured and has a shadowy extinction. One section. 



Age. Archean. 



Remark. The old feldspars here are not so much decayed, but crushed and 

 recemented. N. H. w. 



No. 1994. GRANITE. (Red.) 



N. W. y sec. 23, T. 63-17, north part of Vermilion lake. 

 Ref. Annual Report, xxiv, page 2. 



Meg. Dike, three inches wide, cutting mica schist. 



Mic. The rock shows but little contrast between old and new feldspars, but 

 the whole is an interlocking mass of feldspar and quartz, with a trifling amount of 

 chloritized hornblende. The feldspar is slightly colored by hematite, by weathering, 

 and consists of microcline, oligoclase and orthoclase. One section. 



Age. Archean dike. N. H. w. 



No. 1995. GRANITE. (Granitized schist.) 



Same place as No. 1994. 



Kef. Annual Report, xxiv, page 2. 



Meg. This rock, as observed in the field, is a mica schist permeated by granitic 

 elements. 



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