292 THE VERMILION IRON-BEARING DISTRICT. 



The pebbles have been frequently crossed by fractures which divide them 

 into rhomboidal pieces, but have not in general been greatly deformed. 

 The fragments usually retain their relative positions. At least 90 per cent 

 of the pebbles in the conglomerate are rhyolite- and feldspar-porphyry, 

 granite- porphyry, and microgranite, the last of which occurs in numerous 

 exposixres in the immediate vicinity. Intermingled with these in very 

 small quantity are fragments of jasper and greenstone. The fragments of 

 porphyry are well-rounded pebbles, and the conglomerates grade into the 

 finer-grained grits and slates and are occasionally traversed by bands of 

 this finer-grained material, so that there can be no question whatever that 

 they are normal water-deposited conglomerates. 



South of Tower, near milepost 92 on the Duluth and Iron Range Rail- 

 road, there is a cut which passes through the Ogishke conglomerate and 

 the associated Knife Lake slates. The conglomerate is very well exposed on 

 the east side of the road, where the weathered surfaces give one a better 

 opjiortunity to study the different kinds of pebbles in the rock than can be 

 had in the small fresh exposures in the cut. The conglomerate is of essen- 

 tially the same character here as at the exposures near Vermilion Lake. 

 The Knife Lake slates lie north and south of it, and the conglomerate and 

 the overlying slates have been intruded by both acid and basic dikes, the 

 acid dikes apparently corresponding to the Giants Range granite, which 

 forms the main portion of the Mesabi or Giants range bordering the northern 

 ]30rtion of the Mesabi district. This occurrence of the conglomerate at 

 tliis place is evidently due to a subordinate anticline which raised it, erosion 

 having then removed the superimposed slates and exposed the conglomerate 

 as we now find it. The sediments here have all been altered, and now the 

 matrix of the conglomerate and the finer-grained bauds that occur occasion- 

 ally in it have been metamorphosed to amphibole and especially to mica- 

 scliists, whose origin could not be determined but for their association 

 with and gradation into undoubted sediments. 



In the SW. I of sec. 6, T. 61 N., R. 15 W., at the second falls above 

 the bridge on the county road, on the west bank of West Two Rivers, 

 there is a clifi^ consisting of Ogishke conglomerate. This conglomerate is 

 here only a short distance from ellipsoidal greenstone of the Ely formation, 

 which is exposed on the east side of the river, and it consists of numerous 

 pebbles of schistose greenstone, evidently derived from the underlying 



