GEOLOGY OF THE LUZERNE QUADRANGLE 25 



exposures are generally not good in the woods, but most of the rock 

 is there apparently highly foliated, moderately porphyritic grano- 

 syenite or quartz diorite. 



The small area mapped as syenite three-fourths of a mile north- 

 west of Efner lake is somewhat problematical. It is medium 

 grained, dark gray, well foliated and richer in hornblende than the 

 usual syenite. It may be simply a dioritic facies of the syenite or 

 it may possibly represent rather thorough digestion of some of the 

 old gabbro by a local portion of the syenite-granite magma. 



The eastern portion of the area which lies in the southwestern 

 corner of the quadrangle is of particular interest because it con- 

 tains a fairly coarse-grained, highly foliated, biotitic, porphyritic 

 quartz diorite with phenocrysts of pink feldspar set in a greenish 

 gray groundmass. In the western part of the area the rock is more 

 like normal syenite, locally somewhat porphyritic. No. 9 of the 

 table represents a thin section of the rock from the eastern part of 

 this area. 



Outcrops are relatively scarce in the Corinth area where most of 

 the rock seems to be highly foliated, moderately coarse grained, 

 somewhat porphyritic, brown to pinkish. No thin section of this 

 rock was examined, but it is probably a quartz dioritic facies of 

 the syenite much like that east of Hunt lake. Similar rock con- 

 stitutes the small area i^ miles west of Hartman. 



The granite of the quadrangle also varies locally to quartz diorite 

 as well shown in a big ledge by the road three-fourths of a mile 

 north of the mouth of Ferguson brook. A thin section (no. 26 of 

 the table) of this rock shows it to be a true quartz diorite. 



Medium-grained granite. This rock occupies fully one-half of 

 the area of the quadrangle, and it is by far the most extensive 

 formation separately represented on the accompanying geologic 

 map. Rock of similar character is abundantly developed through- 

 out the Adirondacks. Most of the statements above made in regard 

 to the foliation, granularity and granulation of the syenite also 

 apply to this granite which is but a facies of the syenite. 



The color of the great bulk of the granite is pink of varying 

 shades, but locally it is light brown to greenish gray. Most of the 

 rock is moderately foliated ; some shows little or no foliation ; while 

 local portions are highly foliated. In addition to quartz and feld- 

 spar the only minerals generally recognizable with the naked eye 

 are hornblende and biotite, either one of these alone or both almost 

 invariably being present. Magnetite, apatite and zircon are seldom 



