GEOLOGY OF THE LUZERNE QUADRANGLE 15 



good exposures covering most of an acre. Lumps of serpentinous 

 material are common within, the limestone. The small narrow area 

 2% miles northwest of Stony Creek village consists of fairly well- 

 bedded pyroxene-garnet gneiss, mostly " rusty " in appearance 

 probably due to weathering of contained pyrite. 



Areas west of ConklingviUe. At the old graphite mine 1%. miles 

 west of ConklingviUe there is a lens of Grenville strata in the large 

 area of Grenville and granite mixed rocks. The rocks are mainly 

 garnet gneiss, graphitic schist (the so-called "ore rock"), some 

 quartzite, and a very little limestone altogether forming a lens about 

 40 feet wide with strike variably northwest and dip 40 to 50 de- 

 grees north. The locality is more fully described in the chapter on 

 Mines and Quarries, 



At the edge of the quadrangle 3^ miles west of ConklingviUe 

 a small lens of nearly pure Grenville quartzite occurs within the 

 mixed rock area. 



Jeffers mountain areas. On the south face of Jefifers mountain 

 a lens of pure quartzite 5 rods long lies in the granite parallel to its 

 foliation. 



By the main road on the south side of the river three-fourths of 

 a mile west of the summit of Jeffers mountain, pure well-bedded 

 Grenville quartzite, showing a thickness of 25 feet, lies against 

 granite (see map). 



Gabbro and Metagabbro 



General features. Most of the rocks here discussed are to be 

 classed as true gabbro and metagabbro younger than the Grenville 

 series and older than the syenite-granite series. The true gabbro is 

 commonly very massive, medium grained, and very dark with good 

 to poor ophitic texture. In many cases a magmatic flow-structure 

 foliation is locally well developed. Another type of foliation, which 

 is common and clearly secondary, has resulted from the pressure 

 upon bodies of the gabbro where they have been caught up in the 

 syenite or granite magma. 



The massive gabbro, where it is free from contamination with 

 granite or pegmatic intrusions, generally contains about 50 per cent 

 of plagioclase (andesine to labradorite), hornblende, hypersthene 

 diallage, biotite, in some cases olivine and garnet, and usually small 

 quantities of magnetite, pyrite and apatite. Pleochroism of the 

 hornblende is generally from green to grefenish yellow; of the 

 hypersthene from greenish gray to pale reddish brown; and of the 



