GRANITIZATION OF ACIDIC LOWER HURONIAN SCHISTS 241 



My reasons for thinking that the gneiss areas within the Post- 

 Huronian eruptives are of the same age as the Lower Huronian 

 schists and not earher (as was the original idea of Sir WiUiam Logan 

 and the earher Canadian geologists) is perhaps a negative one, 

 namely: there is absolutely no evidence of an unconformity between 

 the gneisses and the schists.^ 



Of course, the gneiss may not be, as I suggest, a highly metamor- 

 phosed granite, or rock of similar lithological composition and origin. 

 It may be a metamorphosed aluminous sediment, but, judging from 

 the extreme rarity of rocks of such character in the Lower Huronian, 

 this hardly seems likely, though dynamic agencies competent to 

 cause regranitization of Lower Huronian acid eruptives may with 

 considerable justice be considered capable of utterly destroying the 

 identity of water-laid sediments. 



Since there are no granites now outcropping similar to those 

 exhibited by certain of the pebbles of the Dore conglomerate, it 

 stands to reason that the granite from which they were derived must 

 either be entirely covered by more recent rocks, or else have altered 

 its state. The former hardly seems likely, because the area is large, 

 and the granite pebbles of this particular sort occur everywhere 

 within the Dore conglomerate. In favor of the second hypothesis — 

 namely, a change of state — it may be said that wherever gneiss and 

 granite areas occur together (which is very frequently the case) there 

 seems to be some shght evidence that the latter is derived from 

 the former. The evidence consists in a peculiar ragged, though 

 sometimes gradual, transitional contact and in the numerous dykelets 

 of granite which ramify through the smaller inclusions of gneiss. It 

 may be objected that this contact is simply one characteristic of any 

 eruptive contact between granite and gneiss. It is of course not my 

 contention that the contact is not an eruptive one, but simply that 

 the granite may be derived from the gneiss. A somewhat homely 

 illustration of a similar phenomenon in nature to that of regraniti- 

 zation may be observed in the recrystallization of ice so frequently 

 seen on the surface of a glacier. Here one may often find a very 

 much banded mass of ice — the banding being due to compression — 



' According to the International Committee, these schists would be called Kee 

 watin. It will be seen that the geology as sketched in this paper is slightly different 

 from that given by the committee. 



