THE PRECAMBRIAN ROCKS OF THE CANTON QUADRANGLE 43 



The area inclosed, however, is predominantly a micaceous gneiss 

 weathering with a dark rust color, best exposed around the base of 

 the prominent plagioclase pegmatite dike, and farther north, along 

 the brow of the hill back of the first house north of the cemetery. 

 This formation takes part in the structural irregularities which 

 characterize the garnet gneiss near by, but as the outcrops of a 

 formation of this composition are always poor, so in this case also 

 it is impossible to follow the folds in the pyritous gneiss with any 

 precision. 



The third stratum of pyritous gneiss, which is too thin to be indi- 

 cated on the map, outcrops at several points along the brow of the 

 garnet gneiss hills overlooking the lower course of Van Rensselaer 

 creek. It is first observed just east of the north-south zigzag road 

 which crosses the middle of the sigmoidal flexure, then at the end 

 of the next north-south road crossing the creek, next lOO yards be- 

 yond this, then underlying the small lens of granite gneiss in the 

 east wall of the amphitheater, and finally, having been turned upside 

 down by the general flexure of the inclosing gneiss, overlies a band 

 of amphibolite on the north slope of the 980-foot hill on the south- 

 east limb of the sigmoid. The stratum is merely an unusually 

 pyritic layer of mica gneiss. It is not prominently developed nor 

 well exposed, and probably has a maximum thickness of not over 

 10 or 15 feet. As these few outcrops, though separated by one- 

 fourth to one-half of a mile, are in alignment according to the de- 

 mands of the local isoclinal structure, there can be little doubt that 

 whether continuous or not, they represent the same horizon. 

 Toward its eastern end the bed departs from the edge of the garnet 

 gneiss, and when last observed is found near the middle of this for- 

 mation. Were the garnet gneiss conceived to be of igneous origin, 

 this distribution of the pyritic stratum would be in harmony with 

 a partially xenolithic character. In view, however, of the evidence 

 already presented in favor of regarding the garnet rock as of sedi- 

 mentary origin, the pyritic gneiss can hardly be interpreted as other 

 than an interbedded stratum of similar origin. Nevertheless on 

 this basis it is difficult to account for its sudden departure from the 

 edge to the middle of the associated formation, unless this behavior 

 is due to the vagaries of tectonic disturbance or to a stratigraphic 

 thinning out of the underlying garnet gneiss. 



These three occurrences of pyritous gneiss have been mentioned 

 principally to indicate that this type of rock is of rather general dis- 

 tribution in association with Grenville mica gneiss, garnet gneiss 

 and limestone. Though the content of pyrite is not high enough 



