456 



Report of the State Geologist. 



side of the limestone. The latter shows no distinct bedding planes, but the 

 lines of minerals, especially the serpentine, strike about N. 35° E. Scattered 

 through the limestone are bunches of the ferro-raagnesian minerals, pyroxene, 

 mica and hornblende. They form a dark strip several feet wide on the 

 western boundary of the limestone at the north end of the bridge. At the 

 south end and just behind a small barn, the gneiss contains an abundance of 

 magnetite in grains and lumps up to an inch in diameter. The gneiss on the 

 eastern side of the limestone contains much pyroxene along the contact and 

 is distinctly laminated, but farther to the east in the field it contains many 

 coarsely crystalline granite veins. 



Around the Forest-of-Dean mine and the adjoining reservoir, the gneiss 

 is a mixture of quartz, feldspar, hornblende and biotite, the two latter in 

 variable proportion. The gneiss dips southeast and pitches about 22 p to 

 the northeast. The ore-body is described under the economic division of 

 this report. The ore-bed is cut by a camptonite dike and two others occur 

 along the road to the southwest by the reservoir. 



Highland Township. The gneisses of this township are often quite 

 massive. Along the Hudson river the prevailing grey gneiss is composed 

 of quartz, orthoclase and biotite. A little plagioclase is present, and the 

 quartz often contains cavities. The general strike is from N. 40° to SO 1 *' E., 

 and the dip generally to the east. Pegmatite veins are common and form a 

 prominent feature of the gneiss. They usually run parallel to the bedding 

 of the gneiss, rarely cutting across it. and they also commonly partake of the 

 folding or other distortion which the gneiss has undergone, while their 

 boundaries are not always sharply defined. On the road from CranstOns 

 to Fort Montgomery and a short distance north of the latter are several 

 outcrops of graphite schist; it also occurs in the woods to the west and about 

 one and one-half miles southwest of the village of Fort Montgomery, along 

 the road to the Forest-of-Dean mine. In all of these exposures the rock 

 is much decomposed and stained from the disintegration of pyrite. The 

 gneiss is very basic south of Little Long pond, and is intersected by several 

 dik<-. 



Cornwall Township. The gneisses form the southern half of the 

 township, extending from Mountainville around the base of the mountain to 

 Cornwall-on-Hudson. They vary from massive to a bedded variety, and are 

 normally a mixture of quartz, feldspar and biotite, but sometimes contain 

 hornblende in great abundance. Towards Cornwall they become very 

 quartzose and arc seen in contact w ith the Hudson slates along a fault line. 



