GEOLOGY OF THE BROADALBIN QUADRANGLE 1 5 



except for occasional small porphyritic feldspars. The garnet and 

 magnetite are very fine grained and scattered through the rock. 



An extreme variation of the syenite from near the top of Buell 

 mountain is notable for high quartz (25 per cent), magnetite 

 (10 per cent) and biotite (15 per cent) and failure of hornblende. 



Another variation of the rock which in the field, two and one- 

 half miles north-northeast of Batchellerville, looks like typical 

 syenite shows in the slide: 45 per cent orthoclase; 10 per 

 cent plagioclase (andesine to oligoclase) ; 20 per cent quartz; 20 

 per cent hornblende (changing to chlorite) ; 5 per cent magnetite; 

 and small amounts of zircon, apatite and zoisite. This variety is 

 notable for its high hornblende content and lack of microperthite. 

 In still other cases biotite and hornblende occur in the same slide. 



The failure of green pyroxene in the syenite here harmonizes 

 with the observations of Gushing regarding the Adirondack syenites 

 in general, namely, that in the more quartzose varieties the horn- 

 blende is likely to predominate even to the complete exclusion of the 

 pyroxene. 



The syenite from the Round lake area is generally pretty 

 quartzose, has biotite instead of hornblende, and is unusually mas- 

 sive in appearance though clearly gneissoid. It is certainly an in- 

 trusive rock of syenitic or granitic makeup and in the absence of 

 evidence to the contrary is classed with the other syenite of the 

 quadrangle. 



In the small area directly west of Cranberry Creek the rock is a 

 pure syenite but very porphyritic and gneissoid. 



The following analysis of what is regarded as the most typical 

 syenite, from the quarry, near the river, one mile northwest of 

 Northville, has been made for the writer by Professor E. W. Morley: 



Si a 66.35 



AI2 Os , 14.09 



Fe^ O3 1 .81 



Fe 4.49 



Mg 1.05 



Ca 3.16 



Sa= 3.32 



K2 O 4.08 



H. O 35 



Ti O2 1 .00 



P. O. 40 



Mn O 17 



S .04 



CI 02 



F - 03 



Ba O 03 



Zr O trace 



100.39 



