THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 93 



thoroughly metamorphosed amphibolites, is probably to be regarded 

 not as a primary constituent but as one of the products of incipient 

 metamorphism. 



The rock is undoubtedly a mass of partly recrystallized igneous 

 material, but it is more of the nature of gabbro than hyperite, as in 

 the thin section examined olivene and orthorhombic pyroxene are 

 absent, and the ophitic texture characteristic of hyperite in adjoin- 

 ing parts of the Adirondacks is not found. In mineralogical com- 

 position, the rock is Essentially similar to the less altered phases of 

 the gabbroid rocks found in the Pyrites and Pierrepont vicinities, 

 though finer grained than either of these. Granted its igneous 

 nature,, its age is not so readily determined, but the writer is in- 

 clmed to view it as an included fragment of the gabbro formation 

 whose original nature has been unusually well preserved. If the 

 mass were younger than the granite, it is not likely that its elonga- 

 tion and foliation would be discordant with the structure of the 

 granite immediately surrounding it. The basic rock strikes slightly 

 north of west, dips south, and is elongated north-northwest, but 

 locally the schistosity of the country rock is concentric, being par- 

 allel to the surrounding elliptical bands of the gabbro, and at a dis- 

 tance of 50 feet or so strikes north to the northeast. It vrould seem 

 as though the foliation of the gabbro were a relic of a secondary 

 structure induced when the rock was in its original location, and 

 that the great discordance is due to the xenolith having been given 

 a rotary motion while being carried to its present position by the 

 granite magma. Small, elongated, basic strips parallel and close to 

 the boundary of the black rock give the appearance of having been 

 ripped from the large mass during the process. Residual gabbroic 

 rock, competent in kind though perhaps not in quantity to supply 

 fragments of this kind, is found in the belt of amphibolite lying six- 

 tenths of a mile west of this point, and it is not unlikely that this is 

 the formation which in depth locally supplied the granite with the 

 xenoliths in question and with other more numerous inclusions 

 which have been completely altered to the usual type of amphibolite. 



STRUCTURE 



SCHISTOSITY AND PITCH 

 After the foregoing account of the lithologic and age relations 

 existing among the various rock types represented on the Canton 

 quadrangle, a few paragraphs may be devoted to those features 



