l8 NEW YORK STATE MUSEUM 



Special descriptions. It is the present purpose to describe 

 enough masses of the gabbro and metagabbro to give a good idea 

 of the character of the rock and its relation to the syenite-granite 

 series. 



In the area one-half of a mile east of Thurman station most of 

 the rock is medium grained, ver}' massive and non foliated, excellent 

 exposures occurring along the road. A thin section of this gabbro 

 shows the following volume percentages of minerals: labradorite, 

 40; olivine, 18; hornblende, 12; hypersthene, 10; garnet, 6; diallage, 

 5 ; biotite, 5 ; magnetite, 3 ; and a little pyrite and apatite. Certain 

 of the fine large olivines are surrounded by almost perfect, highly 

 granulated, successive reaction rims of hypersthene, plagioclase and 

 garnet. A pegmatite dike several feet wide and 100 feet long cuts 

 the middle southern portion of this gabbro body. The stone quarry 

 on the east side is in granite close to the gabbro border, and the 

 granite contains a clearly defined inclusion of the gabbro several 

 rods wide. This included gabbro is medium grained and slightly 

 ophitic toward its interior, but amphibolitic along its borders with 

 foliation parallel to that of the granite. 



Highly foliated amphibolitic gabbro makes up the small area by 

 the road 13^ miles south of Athol. Several narrow dikes of granite 

 cut it parallel to the foliation. 



The large mass of gabbro at the top of Bald mountain is almost 

 all very typically medium grained and ophitic. 



Much of the gabbro in the area extending westward from the 

 railroad 2 miles south of Athol is foliated and amphibolitic. Around 

 the sides it is intricately cut by granite, as is well shown in a rail- 

 road cut. 



The main bulk of the gabbro in the area i^/t. miles west of Black 

 Spruce mountain is very typical, medium to moderately coarse 

 grained, ophitic and nonfoliated. Near the granite contact, as well 

 exhibited along the brook toward the north, it is foliated and am- 

 phibolitic with many local variations where it is cut by some small 

 granite and pegmatite dikes. 



By the road i^ miles north of Potash mountain a small body of 

 very massive, nonfoliated, medium-grained, moderately ophitic 

 gabbro is cut by one very small aplite dike. This gabbro is fine 

 grained close to the granite. 



The Potash mountain gabbro is largely amphibolitic and cut by 

 several small and large dikes of granite and pegmatite. 



Quartz syenite and pegmatite dikes cut the small body of gabbro 

 \y2 miles north-northwest of Stony Creek village. 



