320 THE VERMILION IRON-BEARING DISTRICT. 



described. This is made up exclusively of both pebbles and matrix of 

 granite debris. The matrix contains many subangular individuals of 

 feldspar, derived in all probability from a porphyritic g-ranite or feldspar- 

 porphyry. In some places the fine graywacke, with the porphyritic 

 feldspars which are associated with the conglomerates, simulates very 

 much a feldspathic porphyi-y. East of this lake are here and there 

 exposures of Ogishke conglomerate, usually in rather' thin beds, asso- 

 ciated with graywackes and slates. About a quarter of a mile south of 

 the small lake just west of Ogishke Muncie Lake, the Ogishke conglom- 

 erate is again exposed in large masses with jasper pebbles present in great 

 abundance. This conglomerate extends eastward to the lake and along its 

 south shore, and eventually is connected with the great mass of conglom- 

 erate to the east of Ogishke Muncie Lake. As we go from the west end 

 of the lake eastward, the jasper pebbles rapidly diminish in quantity, and 

 eventually disappear, so that the conglomerate exposed on the south side of 

 Ogishke Muncie Lake is made up chiefly of pebbles of different varieties 

 of greenstone, with an occasional feldspathic porphyry and granite- 

 porphyry pebble. The typical Ogishke conglomerate also occurs north of 

 the west end of Ogishke Muncie Lake and is likewise exposed along the 

 greater portion of the north shore of the lake. Here it is in all cases the 

 typical jasper-bearing Ogishke, and this may be followed over the areas 

 outlined on the maps and traced with almost continuous exposures through 

 to West GruU Lake. It will be noted that we have here the two phases of 

 Ogishke conglomerate — that known as the typical form, consisting of 

 striking red jasper pebbles with large quantities of granite and greenstone, 

 and that variety which consists essentially of greenstone pebbles with no 

 jasper pebbles and only a few granite pebbles — separated from each other 

 by the width of the lake — about half a mile. Between these lies a syncline 

 of the Knife Lake slates. As these phases of the conglomerate are followed 

 to the east the distance between them gradually increases, a headland con- 

 sisting of Ely greenstone and granite of Saganaga Lake coming in between. 

 These conglomerates are evidently the same. The difference in petro- 

 graphic character can be readily explained as due to a difference in the 

 underlying rocks from which they were derived. North of the headland 

 of Ely greenstone and granite of Saganaga Lake the conglomerate con- 

 sists, to a great extent, of pebbles of granite derived from the granite of 



