34 NEW YORK STATE MUSEUM 



an 8-foot boulder of syenite has in it several distinct inclusions of 

 Whiteface anorthosite, these usually not showing very sharp con- 

 tacts against the syenite. On top of the hill in the area of syenite- 

 granite and Grenville mixed gneisses, there are some small lenses 

 of Whiteface anorthosite in the syenite parallel to its foliation. 

 Near the middle of the northern boundary of the area of Keene 

 gneiss i^ miles west of East Kilns, a big ledge of typical syenite 

 has many inclusions of Whiteface anorthosite which are bunches, 

 lenses or bands from 2 or 3 inches to several yards long. Their 

 borders are not always sharp against the syenite. This is one of 

 the finest exhibitions of such phenomena observed by the writer 

 within the quadrangle. 



In the area of Whiteface anorthosite and syenite mixed gneisses 

 from one-half to 2 miles east of High fall, the anorthosite has been 

 much cut up by intrusions of syenite, good contacts having been 

 noted at several places, but neither definite dikes of syenite nor 

 inclusions of anorthosite were observed in this rough-wooded area. 



The Syenite-granite Series 



The syenite-granite series, prominently developed in the Lake 

 Placid quadrangle, comprises a variable lot of rocks all of which, 

 with one possible exception, are, apparently, facies of a single great 

 cooling magma. Most common is a quartz syenite which grades 

 into a basic (dioritic or gabbroic) facies on one side, and through 

 granitic syenite to medium-grained granite or coarse-grained 

 (usually porphyritic) granite on the other. Since such rocks, which 

 are very abundant in the Adirondack region, have been described 

 in detail in various State Museum bulletins and in other publica- 

 tions on Adirondack geology, no lengthy descriptions will be given 

 in this bulletin. 



That the syenite-granite series is younger than the anorthosite 

 series has already been shown in the discussion of the anorthosite. 



Quartz syenite. This is the most common and typical facies 

 of the syenite-granite series. It is known to occupy approximately 



35 square miles in very irregular areas mostly in the southern half 

 of the quadrangle. In areal extent it is, therefore, about the same 

 as the Marcy anorthosite but not so great as the Whiteface 

 anorthosite. 



As usual in the Adirondacks, this typical syenite is a medium- 

 grained rock, dark greenish gray where fresh, and it weathers to a 

 light brown. In some places a pinkish gray weathering was noted. 



