THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 7I 



Such Optical irregularities are of course intimately related to the 

 degree of deformation which the various areas have undergone. 

 The Canton granite and that southwest of this village are only rel- 

 atively slightly affected by the intense crustal disturbances which 

 doubled the rocks of the Pierrepont vicinity into a tightly com- 

 pressed pitching isoclinal fold. The mass of gabbro-diorite at Py- 

 rites has apparently been a source of local intensification in the 

 deformation of the neighboring granite, for although the extreme 

 of granulation and optical strain of the sigmoid granites have not 

 here been attained, nevertheless the feldspars uniformly show the 

 effects of greater optical stress than do those of the more westerly 

 granites. As intimated, the feldspars of the sigmoid granites and 

 their variants have yielded to the deformative strain to a much more 

 marked degree than those of any other part of the quadrangle. 

 Plate 12, lower figure, taken from a thin section of a modified 

 granite of dioritic composition occupying the outer border of the 

 eastern flexure of the Pierrepont sigmoid, admirably illustrates the 

 optical anomalies and incipient granulation which are incidental to 

 isocline formation in the deeper zones of the earth's crust. The 

 following scale of progressive intensity is suggested by compara- 

 tive observations on the different stages of deformation in the 

 several areas of granite and its modified phases: (i) recrystalliza- 

 tion of the quartz, including microcline formation, (2) production 

 of optical anomalies in the plagioclase spar, (3) granulation of de- 

 formed feldspars and recrystallized quartz. Though it seems prob- 

 able that in this series there is an overlapping of the eff-ects proper 

 to the separate zones of flowage and of fracture, which would 

 prevent its being applied as a universal criterion of the progress of 

 regional metamorphism, it is nevertheless of local adaptability, and 

 agrees fairly well with deductions based on broader areal and 

 structural features. Thus the granite areas which are characterized 

 by quartz recrystallization without plagioclase deformation are the 

 broad belts south and west of Canton, which show ordinarily a 

 gneissoid structure but otherwise no special tectonic activity. 

 Those in which the plagioclase is also affected have been subjected 

 in addition to the generally superimposed regional pressure, to a 

 local deformative influence of no insignificant power originating 

 in the resistant gabbroid buttress at Pyrites interposed between the 

 adjacent bosslike bodies of granite. Those in which granulation 

 has been added to the effects already enumerated are in the area of 

 most intense tectonic activity, the isoclinal belt south of Pierrepotat 



