r88 NEW YORK STATE MUSEUM 



Microscopic characters 



The coarser and more acid syenite at the village (nos. 1, 2) is 

 composed of feldspar, quartz, hornblende and biotite, with acces- 

 sory magnetite, apatite, zircon and pyrite. In much of the rock 

 the hornblende is not fresh but gone to a chloritic aggregate, and 

 at times a little calcite has developed. The accessory minerals 

 call for no comment, except to note that the presence of consider- 

 able zircon i& the rule in all the Adirondack syenite, and that 

 apatite is more abundant here than is usual. 



The feldspar augen show universally a well marked, micro- 

 perthitic structure, of fine rather than coarse fiber. All show 

 strain shadows, and unmistakable ruptured fragments show fre- 

 quently. The body of the rock consists of a fine mosaic of feld- 

 spar fragments separated by quartzose bands and strings of the 

 dark silicates. This feldspar seems to have entirely recrystal- 

 lized. Little oligoclase individuals appear here and there, and 

 an occasional fragment shows microperthitic structure, but in 

 most no trace of this can be detected. The lack of this structure, 

 and of the numerous opaque, dotlike inclusions which character- 

 ize the augen indicate that these fragments can not have origi- 

 nated by a simple breakage. The chemical analysis shows how- 

 ever that they must have closely the same composition as the 

 augen feldspars from which their material was in all probability 

 derived. Numerous grains of micropegmatite, certainly quite 

 secondary, also appear in this mosaic. Feldspar constitutes from 

 70^ to lofc of the rock. 



Quartz is next in abundance and makes on an average 15^ of 

 the rock. No quartz augen are to be seen, but the thin section 

 shows it to be disposed in thin leaves of fragmental material, the 

 fragments being of much larger size than the mosaic feldspar. It 

 recalls similar leaf quartz from other syenites and granites in 

 the Adirondacks, though the leaves are much more broken into 

 fragments than usual. Many of these show strain shadows and 

 are full of inclusions similar to those found in the feldspar augen, 

 and it would appear that the quartz was more plastic than the 

 feldspar under the conditions which prevailed during metamorph- 



