PETBOGRAPHIC GEOLOGY AND DESCRIPTIONS. 771 



Quartz-feldspar schist.] 



There are, at the same time, fewer of the "old feldspars" now apparent, and hence 

 the granulitic structure has the appearance of a second generation from a molten 

 rock, there being no visible schistosity. One section. 

 Age. Archeau (metamorphosed Keewatin). 



No. 1729. QUARTZ-FELDSPAR SCHIST. 



North side of the same point, in a narrow westward -running bay. (Not shown on the township plats ) 

 Underlies No. 1728. 



Ref. Annual Report, xxi, page 157. 



Meg. Appearing porphyritic with feldspar. 



Mic. This differs from No. 1724 in the following respects: Quartz less common, 

 almost wanting, but present in the finer portion of the slide, and in one case devel- 

 oped in the central part of the feldspar; the feldspars are frequently large, giving a 

 porphyritic facies, but they are decayed about their margins and over large irregular 

 areas, the little sericitic scales being uniformly prevalent. These large feldspars are 

 much twinned on the Carlsbad, albite and pericline plans, and having an extinction 

 on Kp of 86 seem to be near anorthoclase or microcline-anorthoclase. Numerous 

 smaller fragments of the same feldspar are in various stages of decay even to total 

 obliteration. In case of the complete disappearance of a smaller feldspar grain its 

 former presence is only evinced by the existence of a finely granular spot in the 

 slide, the replacing minex-als being interlocking fine feldspars, sericite and hornblende, 

 like the same minerals in the slide at large, but usually with less of the hornblendic 

 element. It is of course probable that all the finest original feldspathic debris has 

 thus been replaced, and that the feldspars remaining visible are only visible because 

 of their greater size, and hence greater endurance. There is no schistose structure. 

 The rock suggests esterellyte. 



Age. Archean (Keewatin). N. H. w. 



No. 1730. QUARTZ-FELDSPAR SCHIST. (Kpidolic.) 



At the same place as No. 172',). 

 Ref. Annual Report, xxi, page 157. 



Meg. Somewhat porphyritic with feldspars, irregularly associated with and 

 blending into No. 1731. 



Mic. The porphyritic aspect is due, as in No. 1729, to the occurrence of numer- 

 ous clastic fragments of feldspar of large size. These are, however, very much 

 altered, crowded with epidote, sericite and zoisite and almost lost in the general gran- 

 ulation; indeed, it appears that many of the smaller feldspar fragments have become 

 entirely unidentifiable as such by reason of this tendency to fine granular disinte- 

 gration and the generation of secondary interlocking quartz and feldspar. This gives 

 the rock in general a fine micro-granitic structure. The large amount of epidote, 



