214 The Ottawa Naturalist. [February 



hand it appeared to be equally certain that the same plutonic 

 igneous material was at other points, not far distant, intrusive 

 through precisely similar strata. Such apparently contradictory 

 evidence in regard to the geological relations of these rock masses, 

 remained unexplained until the discovery of the extensive series 

 of exposures of similar rocks in the northern part of the town- 

 ship of Tudor. Here, the evidence was very complete and 

 convincing that the supposed conglomerates were in reality 

 autoclastic rocks and the so-called pebbles extremely deformed 

 portions of a series of more or less parallel dykes, evidently 

 highly differentiated apophyses of the neighboring parent 

 plutonic mass. The diversity in composition of the coarse frag- 

 ments, at first urged as one of the strongest proofs of iheir 

 clastic origin, is believed now to depend on the com- 

 position of the neighboring irruptive mass. The whole 

 series of exposures illustrate in great perfection c\cr\' gradation 

 in the process of the formation of these seeming elastics, showing 

 how exceeding difficult it is, if not impossible, in cases ofcvtreme 

 deformation and movement, to distinguish between these auto- 

 clastic rocks and the ordinary coarse fragmentals characteristic 

 ,of littoral action. 



Exposures of these rocks which have suffered least from 

 dynamic action, show a series of very approximately parallel 

 bands or dykes generally of whitish or very light greyish rock 

 embedded in and apparently cutting a dark grey almost black 

 micaceous schist. Precisely similar phenomena are rather 

 familiar to most workers in Archaean geology, and 

 are characteristic of intrusive contacts, where the more acid 

 plutonics come against darker coloured schistose material. The 

 contrast in colour is most marked, and this is further accentuated 

 by the kaolinization of the felspar so abundant in the lighter 

 coloured portion of outcrops which have exposed to atmospheric 

 decay. The action of the weather seems to be relatively more 

 severe with the darker portions of the rock, causing these to dis- 

 integrate more rapidly and leaving the lighter coloured areas in 

 rather prominent relief The length of these lighter coloured 



