GEOLOGY OF THE LAKE PLACID QUADRANGLE 33 



dence of the sort in the northern portion of the great body of 

 anorthosite demonstrating that tlie syenite-granite series is younger 

 than the anorthosite. In fact the only other evidence of this kind 

 thus far pubUshed is the important discovery by Professor Gushing 

 of dikes of syenite cutting the western margin of the anorthosite 

 in the Long Lake quadrangle.^ 



One mile south of Morgan pond, on a prominent spur of Wil- 

 mington mountain, two tongues or dikes of quartz syenite, clearly 

 exposed for 50 or 60 feet, cut through a big bare ledge of White- 

 face anorthosite (see map). The dikes are from 10 to 20 feet 

 ivide, and they are quite certainly off-shoots from the considerable 

 body of quartz syenite which lies to the west. As would be expected 

 in such narrow dikelike masses, the syenite is somewhat finer 

 grained than usual, but otherwise it is quite normal. No. 39 of 

 table 2 gives the mineral composition of a thin section from one 

 of the dikes. The dike rock has weathered moderately to a light 

 brown. It is very slightly gneissoid. The contacts against the 

 anorthosite are not perfectly sharp and there may have been very 

 slight assimilation along the borders. 



Along the brook three-fourths of a mile west of The Flume, a 

 tongue of quite normal quartz syenite 20 feet wide cuts typical 

 Marcy anorthosite. This dike is an ofif-shoot from the considerable 

 body of similar syenite extending southwestward (see map). 



On the mountain spur i}i rniles northeast of the summit of 

 Little Whiteface mountain, a number of tongues of granite cut the 

 Whiteface anorthosite. The relations are very clear in the big 

 bare ledges. Of the three tongues of granite, shown on the map 

 in somewhat exaggerated form, the middle one is only 20 feet wide, 

 while the other two are some rods in width. The dike granite 

 contains several per cent of hornblende, is clearly gneissoid, and 

 weathers to pink or brown. South of the dikes just mentioned, 

 several tongues of granitic syenite, none over 2 or 3 feet wide, cut 

 the typical Whiteface anorthosite. 



Inclusions of Whiteface anorthosite in syenite and granite, fur- 

 nishing decisive evidence that the syenite-granite series is the 

 younger, were observed at a number of localities. A few of these 

 will be cited. Ledges of syenite by the river one-fourth of a mile 

 east of High fall contain inclusions of Whiteface anorthosite 

 arranged parallel to the foliation of the syenite. Near the base of 

 Little High fall three-faurths of a mile northeast of High fall, 



*N. Y. State Mus. Bui. 115, p. 479-82. 1907. 

 2 



