﻿40 NEW YORK STATE MUSEUM 



finally we get a rock in which but few unmashed feldspar centers 

 remain, the hornblende has entirely disappeared, and the rock 

 is a finely granular aggregate of feldspars, mica scales, and 

 some quartz. 



Of accessory minerals, apatite and titanite are prominent, the 

 former being abundant for this mineral, and of good size, the 

 latter usually rimming the magnetite, as well as occurring away 

 from it. The feldspars comprise microcline, microperthite and 

 plagioclase (oligoclase-andesine), with the latter somewhat in 

 excess when the plagioclase in the microperthite is included with 

 it. The quantity of the two, however, is not far from equal in 

 most cases. There is little or no quartz in the least mashed rock, 

 and the quantity steadily increases in the gneissoid varieties. 

 Some of this increase is certainly due to reactions during recrys- 

 tallization since quartz commences to appear with the appear- 

 ance of biotite. On the other hand the rock varies somewhat 

 in acidity and some of the quartz is unquestionably primary. 



The coarse augen gneiss at the south has much the same 

 mineralogy as the remainder, though more quartzose and acid, 

 approaching a granite in composition. Smyth holds the view 

 that it is a separate intrusion from the main mass of the syenite, 

 and older, having noted an exposure in which the syenite 

 appeared to cut the augen gneiss. We did not have the good 

 fortune to observe any such exposure, hence his positive evidence 

 must outweigh our lack of such. Chemically also the augen 

 gneiss is much more acid than the syenite, being remarkably 

 like the Picton granite in composition. If the two are separate, 

 the augen gneiss is the older, and both are younger than the 

 Laurentian, while the Picton holds inclusions of the augen gneiss. 



This syenite differs considerably from the usual type of syenite 

 of the Adirondack region, represented here by the Theresa 

 syenite, both in general appearance and in mineralogy. Analyses 

 and more detailed description will be given in a later section of 

 this report. It is more gneissoid, giving the appearance of 

 greater deformation than the Theresa syenite, and hence it is 

 tentatively inferred that it is somewhat older than that. The 

 appearance may however be entirely deceptive, since the one 

 rock gives rise to abundant mica when deformed, and the other 

 furnishes little or none, nor any other mineral which promotes 

 foliation. Hence the same amount of deformation would produce 

 a better foliated rock in the former case than in the latter, a 

 rock which would appear more greatly deformed. 



