THE PRECAAIBRIAN ROCKS OF THE CANTON QUADRANGLE 47 



these inclusions of pyritic gneiss have had substantially the history 

 indicated above. 



QUARTZITE AND QUARTZ-SCHIST 

 Ouartzite and quartz-schist are comparatively unimportant in the 

 Canton quadrangle, both the quartzitic schists and. the true quartz- 

 ites being limited to some half dozen occurrences. This point is 

 of interest when it is recalled that in the Thousand Islands vicinity 

 (Gushing et al. 1910, pages 31-32) quartzite is one of the prorni- 

 nent Grenville formations. In the present instance it is not only 

 of no areal consequence, but by reason of its restricted development 

 it likewise possesses no special structural interest. Its main ex- 

 posures are found at three places along the Grass river, reaching 

 from a point four-tenths of a mile due east of the railroad trestle 

 to a point a few rods north of Stevens's limestone quarry. The 

 largest of these occurrences is at the south end of the quartzitic 

 strip as mapped and with its abundant snow-white roches mouton- 

 ees, forms a rough and somewhat picturesque topography, 



The rock is a pure white vitreous quartzite, hard and tough, and 

 free from any trace of bedding which would suggest its attitude or 

 structure. It is surmounted along its western side by an irregular 

 outlier of Potsdam conglomerate, of very similar physical charac- 

 teristics, whose discrimination from solid undecomposed Grenville 

 quartzite is a matter of some difficulty. This occurrence of quartz- 

 ite is mapped so as to extend across the river at Woodcock's rapids, 

 in order to indicate the possibility of its connection, after much thin- 

 ning out, with the ledges north and south of Stevens's limestone 

 quarry. 



The southerly of these outcrops, forming a small knoll on the left 

 bank of the river, is a white sugary quartzite not so tough as the 

 first, and with a thin interbedded layer of rusty gneiss. The north- 

 erly outcrop is in a cut or prospect in the hillside which exposes a 

 slightly banded layer of vitreous quartzite a few feet thick, highly 

 charged with disseminated pyrite. If these two outcrops on the left 

 bank of the river are parts of a continuous stratum, and the strike 

 maintains the direction indicated in the individual ledges, then this 

 bed of quartzite overlies the limestone which was formerly quarried 

 at the intermediate point. These last two occurrences are of some- 

 what different character than that first described, and may not be 

 continuous with it. Their being mapped as such is merely intended 

 to emphasize the presence of a quartzitic streak along the middle 

 of the Grass River limestone belt in this vicinity. 



