22 NEW YORK STATE MUSEUM 



tongues of syenite cutting the Grenville and clearly defined inclu- 

 sions of Grenville in the syenite. According to the work of Gush- 

 ing on the Long Lake quadrangle, the syenite is also younger than, 

 and intrusive into, the anorthosite.^ For most part at least, the 

 granites of the Blue Mountain quadrangle are only differentiation 

 phases of the great syenite body and of practically the same age 

 as the syenite, though the possible presence of some unproved 

 granite either distinctly older or younger than the syenite must be 

 admitted. This matter is more fully discussed in connection with 

 the granite. Both the gabbro stocks or dikes and the diabase dikes 

 are certainly younger than the syenite. 



Normal quartz syenite. More than one-third of the area of 

 the quadrangle is occupied by the normal syenite, it being widely 

 distributed in exceedingly irregular bodies. 



As usual throughout the Adirondacks, the nornial or most 

 typical syenite is dark greenish gray when fresh and weathers to a 

 light brown, though apparently fresh pinkish or reddish syenites do 

 occur rather locally. The depth of weathering usually varies from a 

 fraction of an inch to several inches or, more locally, to a foot 

 or more. In general the amount of weathered rock here seems to 

 be greater than in the border regions of the Adirondacks, doubt- 

 less due to the fact that the central region was neither so long nor 

 so vigorously glaciated. Immediate surfaces of syenite ledges are 

 sometimes light gray to almost white, probably due to the leaching 

 out of iron compounds by water rich in decomposing organic 

 matter. A case in point is the big, bare ledge which looks like a 

 snow bank in midsummer well up on the side of Blue mountain 

 and clearly visible from the south for some miles. A hand speci- 

 men from this ledge shows a thin, white surface layer under 

 which is a brown zone an inch thick and which in turn merges 

 downward into the greenish gray fresh rock. 



As regards granularity, the normal syenite is mostly medium 

 grained; that is, the crystals range in length from I to 5 mm. 

 Sometimes, however, it is finer grained while again it becomes 

 moderately coarse to even slightly porphyritic. More or less granu- 

 lation of the rock is a very common feature, the feldspars showing 

 the greatest effect of the crushing of the mineral grains. 



All the rock is foHated, most of it moderately so. At times the 

 foliation is very faint, while at other times it is excessively devel- 

 oped, especially along shear zones where the rock may have an 

 almost schistose appearance. 



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



