14 NEW YORK STATE MUSEUM 



cent estimates of Professor Adams for the Grenville of Canada. 

 Beginning at the west the base of this section is quartzite, in thin 

 to thick beds, about 800 feet thick, which grades into graphitic 

 (feldspar-c[uartz-garnet-biotite) rather thin-bedded gneisses ap- 

 proximately 1500 feet thick. Then come something Hke 6000 feet 

 of thicker bedded feldspar-quartz-garnet-biotite gneisses which are 

 succeeded b}^ about 500 feet of thin bedded quartzites. Finally, at 

 the summit of the section, come at least 1000 feet of gray garnet 

 gneisses. The upper quartzite is not thought to be a repetition of 

 the lower quartzite because it is thinner bedded, more impure, and 

 is not succeeded by the graphitic beds. There is, of course, the 

 possibility that profound faulting has affected the section but there 

 is no evidence for this in the field. 



SYENITE 



The syenite as here described is regarded as being of the same 

 age and general character as similar rocks so common in the Adi- 

 rondacks. Within the quadrangle the rock shows its igneous origin 

 by its composition and uniform character in large masses as well 

 as by its relation to the Grenville. It is clearly intrusive into, and 

 therefore younger than, the Grenville as proved by frequent inclu- 

 sions of the latter rock within its mass. In the field the homo- 

 geneous appearance of the syenite is in marked contrast to the 

 variable Grenville. The rock always shows a distinct gneissic struc- 

 ture which is often so straight and well developed as to give a 

 schistose appearance. The color of the fresh rock is greenish to 

 light gray and it weathers to a light brown. The main mass of the 

 rock is usually medium grained but it is frequently fairly porphyritic 

 with phenocrysts (up to one-half inch) of feldspar more or less 

 drawn out parallel to the foliation. In thin section the syenite, is 

 usually highly granulated and this, together with the frequent 

 schistose character, indicates that it has been subjected to very in- 

 tense compression. 



Perhaps the best representative of the average syenite of the 

 quadrangle is the mass forming the high hill to the north of North- 

 ville. Under the microscope slides from this rock contain on an 

 average: 25 per cent orthoclase; 18 per cent microperthite ; 8 per 

 cent plagioclase (oHgoclase) ; 22 per cent quartz; 15 per cent horn- 

 blende ; 6 per cent garnet ; 5 per cent magnetite ; together with a 

 little apatite, zircon and zoisite. This rock is much like Cushing's 

 typical Loon lake syenite except that the pyroxene is here entirely 

 replaced by hornblende. This rock is greenish gray and fine grained 



