118 



PROCEEDINGS OF THE CANADIAN INSTITUTE. 



On a small island in the central portion of the lake, situated about 

 two miles north of the mouth of Astron Bay, the rock, which is here 

 a coarse dioritic or ash-bed agglomerate schist, is traversed by a 

 granitic dyke striking 40'', with the cleavage 

 and longitudinal axes of the agglomerate 

 fragments in a nearly vertical attitude. The 

 ground plan of the dyke is given in the accom- 

 panying diagram (Fig. 2). 



The dyke is of irregular width, has a ragged 

 edge, which at places includes portions of the 

 schist, and is, therefore, taken to be an actual 

 intrusion. Its width varies from one to four 

 feet, and about 21 feet of its length is shown. 

 It is of a dark gray color, is coarsely crystal- 

 Fio. 2. line, and has the composition of a highly 



feldspathic g)'anite, but the crystals have a vjell-marhed foliated 

 arrangement parallel to the strike of the dyke. 



Two and a half miles south-west of Yellow Girl Point, Lake of the 

 Woods, lies a small island about four chains in length from east to 

 west and about two in width. The island is composed of evenly 

 laminated hornblende and micaceo-hornblende schists striking east 

 and west with a northerly dip at a very high angle. At its widest 

 part, the schists of the island, which are quite bare and well exposed, 

 are cut by a curved north and south striking dyke about 15 feet 

 wide, whose relation to the schists is shewn in Fig. 3. 



The schists abut sharply on 

 the dyke on both sides and 

 there is no appreciable differ- 

 ence in the strike of the schists 

 on one side from that on the 

 other. The rock of the dyke 

 is syenitic in composition, be- 

 FiG. 3. ing composed of a preponder- 



ance of a pale yellowish pink orthoclase with a black variety of horn- 

 blende and some quartz, plagioclase and mica. The dyke presents an 

 unmistakable gneissic structure which is best developed along its 

 sides, the rock being more undifferentiated and granitic in the central 

 portions. 



The island lies a little to the north of a larger island (Beacon 



