32 



NEW YORK STATE MUSEUM 



Light quartz and biotite make up the rest of the rock, with the 

 exception of a few pyrite grains. The biotite seems to be associated 

 with an alteration mineral which is probably chlorite. 



This stone, in the thin section, shows evidences of crushing, 

 for the quartz is considerably cracked and the feldspar, which is 

 mostly microcline with some microperthite, is also much cracked. 

 Micropegmatite was also noted and the feldspars show kaolinization 

 to some extent. Much titanite, biotite, chlorite, ilmenite, pyrite 

 and magnetite seem to be grouped together in large areas. All 

 of these may be alteration products from a brown titanium-bearing 

 hornblende. A few zircons and apatites were also seen in the 

 section. 



1 1 Gneiss 



Little Falls, Herkimer co. N. Y. 



HALLIMAN BROS. 

 See plate 16 



This is an augen gneiss which is being used for road metal and 

 has been used, to some extent, in the construction of local buildings. 

 The color is prevailingly greenish gray, though, in places, it is rather 

 pinkish. The feldspar eyes are well defined in some places. The 

 texture, as a whole, is rather fine. 



The microscope showed that the eyes are made up of microper- 

 thite around which is a fine grained matrix of quartz and feldspar 

 which has weathered to mica in some places. Through these 

 large crystals of microperthite are stringers of quartz and feldspar. 

 Green hornblende, apatites and magnetite grains were also noted 

 in the section. 



14 Granite 



Northville, Fulton co. N.Y. 



NORTHVILLE GRANITE 8c MARBLE CO. 

 See plate 17 



This garnetiferous gneissic granite has been quarried only on a 

 small scale for local monuments. The color is quite dark due to 

 the large amount of hornblende in the rock. It is rather coarse 

 grained, though variable in texture. Green feldspar and light 

 quartz are easily recognized and there are many large crystals of 

 garnet, some of them reaching a size of over £ inch. 



In the thin section the feldspar was seen to be largely a soda 

 plagioclase, with some orthoclase which had altered in places to 



