GEOLOGY OF THE LUZERNE QUADRANGLE I9 



The small body of gabbro one-half of a mile east of Stony Creek 

 village is quite clearly a big inclusion in the granite. 



Much of the gabbro in the area i^ miles north v/est of Stony 

 Creek village is medium to moderately coarse grained, ophitic and 

 non foliated, but some of it is well foliated, even the coarse-grained 

 part. Some amphibolite is locally developed. This gabbro is in 

 places cut by small pegmatites, one of which, toward the west end 

 of the area, contains lO to 20 per cent of magnetite. 



In the large area 2 miles south-southeast of Stony Creek village 

 there are many good outcrops. Most of the gabbro is ophitic, non- 

 foliated and medium to moderately coarse grained with crystals 

 ranging up to one-half of an inch long. Along some of the borders 

 it is seen to be amphibolitic where it is cut by a itw granite and 

 pegmatite dikes. 



Just north of the summit of West (Hadley) mountain the small 

 mass of gabbro is amphibolitic and cut by small pegmatite and silex- 

 ite dikes. The nearby granite contains some more or less digested 

 inclusions or shreds and lenses of the amphibolite. 



Big ledges within the area 1% miles west-southwest of Gailey 

 hill is medium grained, nonophitic and more or less foliated. A 

 little north of the road it is cut sharply by an aplite dike 2 inches 

 wide, and also by a small pegmatite dike. By the road the finer 

 grained amphibolitic facies is intricately cut by pegmatitic granite 

 forming a mixed rock. Near the northeastern border of the area 

 the foliated gabbro is cut very intricately by granite and pegmatite, 

 the metagabbro having been more or less shredded and cut to 

 pieces, both the granite and gabbro showing contortions. 



By the state road two-thirds of a mile southeast of Gailey hill 

 most of the rock (see map) is considerably foliated, medium 

 grained, nonophitic gabbro cut locally by pink granite usually par- 

 allel to the foliation, but some small dikes of granite cut across the 

 gabbro foliation. Good outcrops cover about an acre. In thin sec- 

 tion this gabbro shows by volume percentages the following min- 

 erals: plagioclase (oligoclase to labradorite), 51; hypersthene, 21; 

 hornblende, 19; magnetite, 6}4; biotite, 2; apatite, i; and a little 

 pyrite. In some cases, close to the contacts with masses of granite, 

 the metagabbro is finer grained. Also where closely involved with 

 granite the metagabbro is generally distinctly biotitic. Some gran- 

 ite, containing very little digested gabbro, is itself notably biotitic. 

 Toward the middle of this same area the foliated gabbro is cut by 

 considerable pegmatite mostly parallel to the foliation, producing a 



