442 W. J. MILLER ADIRONDACK ANORTHOSITE 



grained, with few dark minerals, and this appears to be quite typical 

 Keene gneiss. All the types mentioned grade into each other. 



On the hillside, one-half of a mile southeast of the hill just mentioned, 

 there are outcrops of a moderately coarse grained, rather gabbroid rock 

 with some labradorite phenocrysts. Its mineralogical composition, num- 

 ber 3 of the above table, shows that it is Keene gneiss with strong anor- 

 thosite affinities. There are still other good exposures in this Sentinel 

 Eange area. 



Sunrise Notch area. — This is the largest area of Keene gneiss in the 

 quadrangle (see figure 1). It is about 3i^ miles long and from one-half 

 to two-thirds of a mile wide. Most of the outcrops are quite typical 

 Keene gneiss, though usually not strongly foliated. The rock is generally 

 medium grained, with scattering labradorite phenocrysts. It weathers 

 brown. 



A locality of special interest is a cliff on the southern border of the 

 area, three-fourths of a mile east of the summit of Sunrise Notch. Most 

 of this rock is very gneissoid and only moderately gabbroid Whiteface 

 anorthosite, a little finer grained than usual. Within this rock there is a 

 wide band of fine grained, very gneissoid, gray rock with a reddish tinge 

 due to numerous tiny garnets. The composition of this local band, num- 

 ber 10 of the above table, causes it to be classed as Keene gneiss with 

 strong syenite affinities. Its contact against the anorthosite is not very 

 sharp. Evidently a dike or tongue of the Keene gneiss magma here in- 

 truded the Whiteface anorthosite near its border, and the temperature 

 was high enough to cause fusion of the anorthosite walls of the dike or 

 tongue. 



Area west of East Kilns. — This area, between 1 and 2 miles west of 

 East Kilns, shows certain interesting and important features. Much of 

 the rock has strong syenite affinities because of the high content of ortho- 

 clase. 



Near the middle of the northern boundary syenite contains inclusions 

 of Whiteface anorthosite as bunches, lenses, and bands from two or three 

 inches to several yards long, the boundaries of the inclusions usually not 

 being very sharp. Evidently very little assimilation of anorthosite took 

 place here. 



Along the northwestern side several ledges are very gabbroid in appear- 

 ance, in some places very gneissoid and in others not. Locally there is 

 very intimately associated syenite and Whiteface anorthosite. Appar- 

 ently these ledges show the effects of partial digestion or assimilation of 

 anorthosite by the syenite magma. 



