THE LOWER HURONIAN. 315 



on the cong'lomerate has been reHeved by movement in the matrix, and 

 this matrix has in most cases been rendered perfectly schistose. It will be 

 fomid that the schistosity, when it approaches a pebble, gradually bends 

 so as to run around the ends of the pebble, and then upon the flat sides 

 continues in its normal direction. 



The contact metamorphism resulting- from the intrusion of igneous 

 rocks seems to have been more far reaching in its character — at least so far 

 as it has produced changes in the petrographic character of the conglom- 

 erate — than the metamorphism due simply to orogenic movement. In all 

 probability the action of the intrusives is complicated by the fact that their 

 intrusion took place subsequent to some orogenic movements, so that they 

 acted on rocks which had already been somewhat metamorphosed. The 

 best area in which to study this contact action is in the vicinity of Snow- 

 bank Lake. Snowbank Lake lies in a granite massive, which has received 

 its name, the Snowbank g-ranite, from the lake. The Ogishke conglom- 

 erate surrounds this lake and is exposed with bare surfaces over large 

 areas. At a considerable distance away from the lake the conglomerate 

 possesses its normal characters, but as the lake is approached it will be 

 seen that gradually it changes. Tliis change is for the most part a petro- 

 graphic one, and has consisted of the production of micaceous and horn- 

 blendic schists from the finer-grained sediments associated with the 

 conglomerates and from the fine matrix between the pebbles of the con- 

 glomerates. The pebbles in the conglomerates have also been altered, 

 certain kinds, of course, very much more than others. In general these 

 finer materials are now well-developed mica-schists in which the conglom- 

 eratic character can, howcA'er, be readily recognized by the presence of 

 comparatively unaltered granite pebbles. This alteration has reached its 

 extreme where the conglomerates are nearest to the granite. 



Long after the intrusion of the granite and the metamorphism of the 

 conglomerates, the Keweenawan gabbro was intruded, and it has in turn 

 modified the conglomerates, which were already metamorphosed hj orogenic 

 movements and by the granite. The effect of the contact action of the gab- 

 bro lias extended for a considerable distance from the present exposures of 

 the gabbro. The exact distance can not be determined with certainty, as 

 its metamorphism blends with that produced by the granite. Possibly 

 a more detailed field and petrographic study than was warranted in the 



