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NEW YORK STATE MUSEUM 



amounts of the ferromagnesian minerals and magnetite. The 

 coarser, massive phase, which may be regarded as the original type, 

 is only occasionally observed in the field, for the whole mass seems 

 to have undergone more or less granulation and recrystallization 

 from pressure metamorphism. This circumstance indicates an 

 earlier period of intrusion for the syenite as compared with the red 

 granite of the same region, though the contact relations where 

 observed did not afford any definite evidence in that particular. 



Microscopic examination. The feldspar is principally a microper- 

 thitic intergrowth of orthoclase and albite, with a little acid plagio- 

 clase. In many places the feldspar constitutes over 80 per cent of 

 the entire rock. A deep green pyroxene is usually observable in 

 small, irregularly bounded individuals with which a darker horn- 

 blende is often associated in a manner suggestive of its derivation 

 from the pyroxene. Quartz and magnetite are important accessory 

 minerals, the former being particularly abundant in the more 

 foliated varieties. Zircon and titanite also occur and the presence 

 of a little pyrite may usually be observed. 





Fig. 8. Microscopic appearance of syenite from near Harrisville. Shows 

 groundmass of crushed feldspar, with larger fragments of the original crystals, 

 also a little pyroxene and magnetite 



The syenite often has a porphyritic appearance as the result of 

 crushing which has reduced all but a small remnant of feldspar to 

 a fine, granular aggregate. The texture is seldom perfectly mas- 

 sive. 



Chemical analysis. The chemical character of the syenite is 

 illustrated by the following analyses. No. 1 is of a sample taken 

 from the eastern contact near milestone 56 on the Carthage & 



