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NEW YORK STATE MUSEUM 



of intrusive. Ordinarily they consist only of quartz and varying 

 amounts of orthoclase and plagioclase, and in rare instances may be 

 nearly free of quartz and consist almost wholly of orthoclase or 

 plagioclase (albite-oligoclase). A nearly quartz-free, orthoclase 

 pegmatite dike is found just below the dam. in Canton village. In- 

 truded parallel to the foliation it is thickest (about 15 feet) at 

 the northeast end, and divides in the opposite direction into three 

 tongues which taper southwestward as shown in the diagram 

 (figure 15), the longest extending nearly to the left bank of the 

 river. In its bulkiest portion the crystals of orthoclase attain their 

 maximum size of 6 inches or more, and interlock to form an almost 



DAII 



15 ft. 







^ 1 \ / 











Fig, 15 Coarse-grained sheared quartz-orthoclase dike cutting micaceous 

 pyritous gneiss. Crenulations in gneiss pitch about 30 degrees north-north- 

 west; the dike is foliated parallel to its elongation, (a) Gneiss; (b) coarse 

 pegmatite. 



The mill-dam, below Main street bridge, Canton village. 



massive rock. A thin section, however, taken from a finer-grained 

 portion of one of the smaller tongues, shows the pegmatite, plate 14, 

 upper figure, to have suffered incipient granulation which may be 

 related to the development of a northward pitch (30 degrees) in the 

 intruded garnetiferous biotite schist. A prominent dike, 50 feet by 

 75 feet in diameter, of the plagioclase type, in fact the only one of 

 this kind noted, forms a white knoll seven-tenths of a mile south- 

 southwest of Little River crossroads. The dike is massive, medium- 

 grained, weathers snow-white, cuts Grenville rusty gneiss and is in 

 turn penetrated by a number of white quartz veins. Though some- 

 what abnormal in mineral composition, the plagioclase dike un- 

 doubtedly had its origin in a late differentiation of the magma of 

 the granite boss neighboring it on the west. 



