PETROGRAPHIC GEOLOGY AND DESCRIPTIONS. 815 



Granite.] 



microcline in a pneumatolitic manner, and also itself is converted to a microperthite 

 by the intergrowth of a secondary feldspar along its cleavages. In small amount a 

 vermicular micropegmatyte and other inclusions are formed by the quartz in the 

 microcline, but generally the quartz is grouped by itself in roundish interlocking 

 grains. 



The rock is quite fresh, but that it is a reconstructed rock is indicated by the 

 remains of " old feldspars," though not so evidently as in the granite of Kekequabic 

 lake. These remains are of three sorts: (1) Decayed areas isolated in the midst of 

 otherwise fresh feldspar (quite rare in this rock); (2) Remains of a triclinic feldspar 

 in the midst of orthoclase. These consist of scattered grains having their extinction 

 directions the same and simultaneous; (3) Lines of iron rust (limonite) as inclusions 

 running parallel through the orthoclase, simulating albite twinning bands of a 

 triclinic feldspar from which everything is lost except these lines, which were 

 probably accumulated along the planes of separation between the albite macles, or 

 within the macles themselves. The microperthite itself may be mentioned as a 

 fourth trace of an older state of the feldspars of this granite. Two sections. 



Aye. Archean granite. N. H. w. 



No. 1986. GRANITE. 



Menan island, Vermilion lake. The older of two granite dikes. 



Ref. Annual Report, xv, pages 288-290 ; Annual Report, xxiv, page 1. 



Meg. Two granite dikes, one cutting the other. 



Mic. The rock is made up of "old feldspars," much broken and corroded by the 

 surrounding matrix, lying in a micro-granulitic groundmass, quite resembling the 

 granite already described at Kekequabic lake. These old feldspars never interlock 

 with each other, but they are intimately interlocked about their borders by the 

 secondary fine interlocking groundmass. If two are in contact they have the 

 appearance of having been brought accidentally into that position, and sometimes a 

 broken line of glassy small feldspars, or perhaps only one or two grains or a few 

 scales of mica, have been developed along their contact edges. These old feldspars 

 also frequently have isolated, small, fresh and glassy feldspars and quartz scattered 

 irregularly through them, having independent orientations. The most of them are 

 plainly triclinic and approach oligoclase. Extinction on p is about 85, n s being 

 apparently the bisectrix, thus indicating oligoclase-albite. Microcline appears as one 

 of the fresh feldspathic growths. The small granular and interlocking feldspars are 

 mingled with interlocking quartz; it is impossible from the slide at hand to determine 

 them specifically, for they show no crystallographic characters on which to measure 

 extinction. The section contains a little epidote and sphene and a few scales of mica, 

 but is nearly free from the colored silicates. One section. 



Age. Archean dike. N. H. w. 



