THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 69 



and other parts of the garnet gneiss belt, thick masses of amphi- 

 boHte are met with, which are ahnost or quite unaffected by the 

 acid intrusive in its characteristic pinkish granitic aspect, but this 

 does not apply to those irregular universal " flammen " or tongues 

 of whitish pegmatite which are discussed on page 8i. More- 

 over throughout the zones which are predominantly amphibolitic, 

 the granitic material has a rather uniform development and has 

 produced an injection rock of intermediate texture; but occasion- 

 ally large lenticles or sill-like masses, free from basic contamina- 

 tion, are met with, which may vary from 2 to 25 feet in thickness. 

 The most noteworthy of these granite lenses or sheets are indicated 

 on the map (figure 21), but it is to be remarked that innumerable 

 similar but smaller masses are found scattered throughout the garnet 

 gneiss and amphibolite belts, principally the latter. The largest 

 granite lens is that inclosed wholly in Grenville, three-fourths of a 

 mile south of the Beach Plains Church, in this case probably 150 or 

 200 feet thick. 



In the vicinity immediately south of Pierrepont, the localization 

 of the injected granite to the border zone between the amphibolite 

 and garnet gneiss is emphasized topographically. The outer edge 

 of the gabbroid area is not exposed, but in the low hummocks im- 

 mediately north of the Pierrepont hills, gabbro-diorite and related 

 amphibolitic types are exposed, the outermost of which are prac- 

 tically free from acid material ; as the higher hills are approached, a 

 small amount of injected granite is met with, but not until the 

 higher altitudes are reached (at the jog in the road) does the in- 

 truded granite break through in such quantity as to become by far 

 the most abundant rock. The curving line of abrupt northward- 

 facing hills thus marks the outer edge of a predominantly granitic 

 injection zone which, occupying dift'erent portions of the amphibo- 

 lite belt, can be traced the entire length of the sigmoid (see figure 

 11). On moving southward from the east-west narrow oval hill 

 which causes the jog in the road above referred to, one notices 

 that the granite becomes gradually less abundant in the amphibolite, 

 and that when the garnet zone is reached the distribution of the 

 three types is more nearly equal. Finally, at about the point where 

 the road forks, the granite ceases to be a prominent member of the 

 Precambrian complex. 



This succession, which is in a measure typical of the areal rela- 

 tions of the formations in this vicinity, is probably not duplicated 

 with exactness anywhere else in the sigmoid, because of the rapid 



