IN THE NEIGHBOURHOOD OF STJDBURY, CANADA. 35 



(A) Quartzites. — These rocks vary in colour from almost wliite to 

 grey. The recognizable f ragmcntal grains are commonly from about 

 •005'' to -025" in diameter. The rock consists of quartz, with occa- 

 sional felspar (fragmental), and mica (variable in amount). 



The grains of quartz are generally clear, though microlithic 

 enclosures and exceedingly minute cavities do occur. The slightly 

 ragged outline of the grains, and the way in which they are (so to 

 say) fused oue with another and with the matrix, prove to my mind 

 that there has been secondary enlargement ; but to what extent I 

 cannot determine, for I have not been able to distinguish (as one 

 sometimes can) the true boundary of the original grain. From 

 their general outline I believe them to have been formerly angular. 

 Chalcedonic quartz is also present, sometimes interstitially, some- 

 times in aggregates, and this occasionally may also be an original 

 constituent. The felspar fragments exhibit in some cases the striping 

 of plagioclase and the cross-hatched structure of microcline ; it is 

 possible that these also have been enlarged. The mica, which occurs 

 in scales from about -002" or '003" downwards, is light brown in 

 the darker, colourless or almost so in the lighter quartzites. Their 

 well-formed outlines indicate that, even if there has been a nucleus 

 of detrital origin, they have developed their present boundaries 

 in situ. 



Passing now to the quartzites with marked fragments — altered 

 pebbly sandstones — we find that their matrix strongly confirms the 

 view just expressed (specimens from about one mile west of Wahne- 

 pitae to one mile east of Sudbury Station). Brown mica is more 

 abundant, the flakes are larger, often about '005", and occasionally 



Fig. 1. — If atrial of Conglomerate from the Sudhury District, showing 

 well-develoj)ed mica fidkes associated tuith quartz (the white 

 ground of the figure). X 140. 



even more in length, excellently developed, but without any definite 

 orientation (fig. 1). Smaller films of white mica are intermingled 



d2 



