THE LOWER HURONIAN. 287 



place, and would vitiate any estimates. For these reasons it has been 

 found impossible to determine, even approximately, the thickness of the 

 conglomerate. In places it is wanting or is represented merely by a thin 

 mass. In other places, as, for instance, on Vermilion Lake, it shows great 

 development and must be very thick. 



INTERESTING LOCALITIES. 



The islands in Pike Bay offer good exposures of the typical Ogishke 

 conglomerate of the western area. There are also splendid exposures on 

 the large island in sec. 14, T. 62 N., R. 15 W., and on both sides of Arm- 

 strong' Bay. Smaller exposures occur nearer Tower, one southwest of 

 Tower in SW. ^ of sec. 6, T. 61 N., R. 15 W., another just on the outskirts 

 of Tower, on the south slope of Lee Hill, and another on the south slope of 

 Soudan Hill. 



One of the best places in which to study this conglomerate in its typical 

 development is on the southwest side of Stuntz Island, which lies across the 

 mouth of Stuntz Bay of Vermilion Lake. On the bare exposui-es here the 

 conglomerate is made up of pebbles and bowlders of granite-porphyry, por- 

 phyritic microgranite, rhyolite-porphyry, a feldspathic porphyry, jasper, and 

 comparatively rare fragments of greenstone. The coarsest conglomerate 

 lies near the center of the island and is separated from the acid intrusives 

 to the north by a marked depression. Pebbles of, the intrusives are present 

 in the conglomerate. As we go southward across the exposures the con- 

 glomerate grows finer and occasional beds of grit, striking east and west, 

 occur in it until finally on the extreme southwestern point of the island there 

 may be seen at low water a few feet of typical Knife Lake slates. The 

 evidence here is conclusive that the conglomerate has been derived from 

 the sediments to the north and that there is a gradation from it into the 

 Knife Lake slates to the south. On the highest knob at the west end of the 

 island the conglomerate is penetrated by a number of basic dikes varying 

 from 1^ inches to 6 feet in width. At one place near the highest point nine 

 dikes were counted within a distance of 60 feet, lying essentially parallel 

 and trending a little south of east. These dikes cut across the schistosity 

 and the bedding of the conglomerate and also across the fragments in it, 

 showing sharp contacts. They do not seem to have produced any contact 

 effect on the conglomerate. The dikes themselves are only very slightly 

 schistose, and the schistosity is confined to the edges. 



