r56 NEW YORK STATE MUSEUM 



as rims around the magnetite. They further consist of biotite 

 and hornblende, some 20fc of quartz, and white feldspars, largely 

 andfe'sin, since five fragments in the slide which are properly cut 

 give equal extinctions of from 11° to 20° on opposite sides of the 

 albite twinning plane. The remaining feldspar would seem to 

 be anorthoclase, though this is not certain. These rocks are quite 

 like those associated with the magnetites at Hammondville, 

 Essex CO., and it ie of interest that here also a considerable belt 

 of lean magnetite is associated with the black and white gneisis, 

 and close to the belt of very coarse, basic pegmatite, largely com- 

 posed of coarse hornblende, with plagioclase, titanite and mag- 

 netite in addition, and apparently a pegmatitic development of 

 the black and white gneiss. This ore belt occurs on both sides 

 of the lake and was traced for more than a mile. It may extend 

 much farther. In places, possibly everywhere, the rock at the 

 contact with the ore is a peculiar granulite of somewhat rusty 

 appearance, and containing some 60fc of emerald green pyroxr 

 ene^ orange colored titanite, and abundant orange brown garnet 

 whose shade is very like the deeper color of the pleochroic titanite. 

 The remaining minerals are evenly granular quartz and feldspar, 

 which are exceedingly difficult to distinguish, since the feldspar 

 is very fresh and wholly unmarked. The whole makes a strik- 

 ingly beautiful combin'ation in thin section. Beyond this belt 

 the granitic gneisses appear again. It is difficult to tell whether 

 the ore and associated rocks should be regarded as members of 

 the adjacent Grenville series or not, though a strong impression 

 is produced that such is the case. 



Summary of section. The preceding details show that on the 

 east, south and west the Tupper lake syenite is bordered by a zone 

 of mixed rocks, consisting of very gneissodd syenite involved with 

 granitic gneiss. On the one hand, the syenite is found grading 

 into a granite which bears a strong external resemblance to it 

 and often contains the same augite, the passage from one to the 

 other being wholly unmistakable. On the other hand, there is 

 abundance of a granite, often very gneissoid, which shows always 

 intrusive contacts against the syenite when contacts are exposed, 



