REPORT OF THE DIRECTOR I9II 169 



chemical sediment deposited on the sea bottom, and thus originally 

 interbedded with the other Grenville rocks. This would account 

 for the association of pyrite with the gneisses rather than with 

 crystalline limestones, in agreement with the familiar tendency of 

 the mineral to appear in shales and sandstones rather than lime- 

 stones. Furthermore the tendency in later rocks, as well as in 

 modern muds, for pyrite- to occur in such as are rich in organic 

 matter, finds in the present instance a parallel in the association of 

 pyrite with graphite. This association is quite general for the 

 rusty gneisses and is very striking at the Cole and Stella mines, as 

 already pointed out. Altogether, a consistent explanation of the 

 rusty gneisses and accompanying pyrite seems, at first sight, to be 

 afforded by regarding them simply as metamorphosed pyritiferous 

 and carbonaceous shales and sandstones. 



From an explanation so seductively simple it is difficult to turn, 

 and the writer is of the opinion that, with present evidence, there 

 is much in favor of this view so far as the ordinary rusty gneisses 

 with a little disseminated pyrite are concerned. But in applying the 

 hypothesis to the larger masses represented in the ore deposits, 

 difficulties arise. Here we come in contact with marked concentra- 

 tions of pyrite, in veinlike masses, pods and lenses, often very thick, 

 with much vein quartz and pegmatite containing both pyrite and 

 graphite, the whole presenting little resemblance to sedimentary 

 deposits. Obviously some of these phenomena are entirely outside 

 the realm of sedimentary agencies and there appears to be ample 

 ground for ascribing most of this pronounced concentration to a 

 later period of circulation, involving a large amount -of transfer of 

 material and replacement. 



In view of the well-known tendency of pyrite to circulate and seg- 

 gregate in sedimentary rocks subjected to the action of ordinary 

 ground waters it is quite possible that the process of concentration 

 was begun in this way before the rocks were metamorphosed, and 

 Newland^ regards such premetamorphic concentration as probably of 

 dominant importance. The complete recry stall ization of. meta- 

 morphism would, of course, destroy all the original structural rela- 

 tions between pyrite and the clastic minerals which would show 

 whether the former was original or secondary, and thus after 

 metamorphism it would be impossible to distinguish with certainty 

 between pyrite of sedimentary origin and that resulting from 

 ground water concentration, except as the latter might occur in 



1 Loc. cit. 



