r34 



NEW YORK STATE MUSEUM 



plete series of specimens illustrating the gneiss. Nos. 1 to 5 in- 

 clusive were obtained in the eastern cut of the West Shore rail- 

 road at the Little Nose, and no. G came from the gneiss above 

 the wagon road at the same point. The gneiss strikes parallel 

 with the escarpment, viz, n 25-35 e magnetic, and dips conform- 

 ably with the paleozoics. A quarter of a mile west the railway 

 runs through a cut in the gneiss about 200 yards long. Nos. 7, 8 

 and 9 were obtained in the cut. A half mile farther west, as 

 shown by the third colored area, on the south bank of the Mo- 

 hawk, (see pi. 9) the gneiss appears again, and from it nos. 10, 

 11, 12, and 13 were obtained. At this point the gneiss does not 

 reach as high an altitude above the river as on the east, and it 

 then dips down and disappears. 



If one now crosses to the north side of the river and proceeds 

 eastward, the gneiss first appears where the colored area begins 

 on pi. 9, and attains a hight of about 75 feet above the water, 

 rising even higher to the eastward. Specimens 14, 15 and 16 

 were obtained at this point. Little variation can be noted in 

 the rock. To the east of the " Nose " and the bend of the river 

 there is a large gravel pit of the New York Central railroad. 

 Near the head of the pit is the last outcrop of the gneiss (no. 17) 

 in this immediate vicinity. A heavy talus then covers the gneiss 

 for a long distance around the foot of the escarpment, but it 

 reappears in the town to the north. 



Great interest was felt by us in the petrographic characters of 

 this gneiss, the more because Beecher and Hall had named their 

 lowest outcrops labradorite, and it was inferred that the an- 

 orthosites might outcrop at this remote southern point. Micro- 

 scopic sections were therefore prepared of nos. 2, 4, 5, 6, 10, 11, 

 13 and 17, which were selected to represent all the outcrops and 

 all the varieties. The specimens are practically the same rock, 

 except no. 11, which shows some variation. All the others are 

 garnetiferous gneiss, which under the microscope exhibits quite 

 invariably quartz as the most abundant mineral, and reddish 

 brown biotite as a constant associate. Plagioclase in minor 

 amount is commonly present, and in no. 4, there is a little micro- 



