22 NEW YORK STATE MUSEUM 



MIXED GNEISSES 



Under this heading are included various gneisses but chiefly more 

 or less intimate mixtures of Grenville, syenite, and granite. For 

 most part the Grenville appears to predominate but because of 

 the presence of so much other rock it is thought best to map these 

 mixed gneisses separately. It is often difficult to draw the bound- 

 ary lines between these gneisses and the other rocks because any- 

 thing like sharp contacts are wholly lacking. The Grenville has 

 been much cut up by intrusions of syenite or granite so that small 

 masses of good igneous rock and good Grenville often exist in 

 close proximity. At times rather clear-cut inclusions of Grenville 

 occur within the igneous masses. Again, gneisses are commonly 

 seen which could scarcely be called good Grenville nor yet good 

 syenite or granite, but which in every way look like rocks which 

 may have resulted from the incorporation, by fusion, of Grenville 

 into the molten masses. The more the writer observes these mixed 

 gneisses along the western and southern border of the Adiron- 

 dacks, the more is he impressed with the very strong evidence in 

 favor of assimilation. 



A great variety Of gneisses is shown in the area northeast of Batch- 

 ellerville. Grenville is present to a greater or less extent throughout 

 the area and is at times very pure as, for example, where it forms 

 the wall rock of the feldspar mine on the south side or just east 

 of the end of the branch road shown on the map. Porphyritic 

 granitic looking gneiss is abundant from the mine northward, while 

 syenite shows in large exposures one-third of a mile south of the mine. 

 South of the branch road gray, rather massive, granitelike gneisses 

 are common. 



Due north of Northville the mixed gneiss area, with numerous 

 outcrops, affords a fine illustration of intimately associated Gren- 

 ville, syenite, and granite. The continuation of this area to the 

 west of the river well shows the passage of the mixed gneisses 

 into pure syenite through uninterrupted exposures. The Grenville 

 generally preponderates but often massive syenitic rocks are present. 

 One and one-quarter miles due north of Buell mountain a mass 

 (forty or fifty feet across) of typical thin-bedded Grenville quart- 

 zite forms a clearly defined inclusion in the syenite. 



In the area west-northwest of Cranberry Creek the Grenville is 

 frequently intimately associated with masses of granite porphyry or 

 syenite. The Grenville is often badly twisted and looks like inclu- 

 sions or masses more or less melted in with the igneous rock. 





