20 NEW YORK STATE MUSEUM 



Number i is a fine example of a transition rock from a granitic 

 syenite to granite as seen along the river in big ledges one-half of 

 a mile south of The Glen. The color of the rock is pinkish gray. 

 Especially noteworthy are the comparatively low quartz and high 

 hornblende contents, and the absence of microcline. 



Number 3 is typical looking pink, biotite granite from the granite 

 ridge just west of Crane mountain. 



Number 6 is a very quartzose, hornblende, biotite, pink granite 

 with considerable microcline as seen in excellent outcrops along the 

 road i^ miles south of Riverside. 



Only a few of the observed masses of Grenville or mixed gneisses 

 which occur within the granite are large enough to be shown on 

 the geologic map. Small inclusions or stringers, sometimes sharply 

 outlined and sometimes seeming to grade into the granite, are very 

 numerous. Only a few examples will be cited. Thus, a large, 

 homogeneous mass of very typical granite, one-quarter of a mile 

 above the mouth of Glen brook, contains a number of clear-cut 

 Grenville hornblende gneiss inclusions. These inclusions are 

 mostly long (10 to 20 feet), narrow stringers which are drawn 

 out parallel to the foliation of the granite. Similar inclusions are 

 common i mile south of The Glen along the east bank of the river, 

 and in the Mill mountain mass. On the west bank of the Hudson 

 river and just opposite the Ferry (east of Heath mountain) a 

 ledge of coarse-grained hornblende granite contains ten or fifteen 

 fine examples of small (none over 3 feet long) ver}'- angular in- 

 clusions of Grenville hornblende gneiss. 



Features of special interest in connection with the granites are 

 the frequent and comparatively sudden transitions from the gray 

 to pink varieties, and from the more syenitic or basic facies to the 

 more truly granitic facies. The effect is to give wide bands or 

 layers of varying color and composition and yet all clearly belong- 

 ing to the same rock mass because of the true gradation of one 

 layer or band into another. Among many places where such 

 phenomena have been observed are in the vicinity of The Glen, 

 and along the road one-half of a mile north of the north end of 

 Loon lake. The writer has already described similar occurrences 

 in the region of the Port Leyden quadrangle.^ Professor Kemp, 

 in the bulletin on the Elizabethtown-Port Henry region, has re- 

 cently described and suggested an explanation for similar but even 

 more extreme phenomena as follows: ''The most acidic variety 

 will quite sharply replace it [the syenite] ; and in the same way a 



1 N. Y. State Mus. Bui. 135, p. 16-17. 



