UPPER HURONIAN. 389 



along the north side of the road leading to Fay Lake, where it is verj thin, 

 but to the west it increases greatly in thickness, until it is found covering 

 an area having a width north and south of nearly a mile along the line 

 between sees. 26 and 27, T 65 N., R. 5 W. The Gunflint formation has 

 been found in direct contact with this conglomerate at a number of places, 

 but in no place could a conglomerate be found which could be said to be at 

 the base of the Gunflint formation and separable from the Ogishke con- 

 glomerate. At no place in this district can positive evidence be found of 

 the relation of the Gunflint formation to the underlying Lower Hui'onian 

 series. Wliere these rocks are in contact no strike or dip could be found in 

 the conglomerates below the iron-bearing formation. The strike and dip 

 can be determined where the iron formation is separated from the Ogishke 

 conglomerate and Knife Lake slates by an area within which there are no 

 exposures. In these cases the strikes of the rocks are nearly at right 

 angles to each other, and there is a great discrepancy in dip. This evi- 

 dence weighed in favor of an unconformable relationship. The evidence 

 was not considered conclusive, for in view of the close folding in the 

 district the possibility was recognized that conformable rocks may have 

 been so folded that with lack of exposures showing the actual connection 

 and transition they may appear unconformable. 



Indubitable proof of the unconformable relationship of the Gunflint 

 iron-bearing- beds to the Lower Huronian series was found by Leith in the 

 Mesabi district.". There the conformable series of rocks — Upper Huronian — 

 to which the Gunflint formation belongs, was found overlying the Lower 

 Huronian series with a basal conglomerate between. Thus the conclusion 

 reached from the study of the imperfectly exposed beds in the Vermilion 

 district was confirmed. 



Relations to the Keiveenaivan (Dulutli) gahhro. — In all cases where the 

 Gunflint formation is exposed in the Vermilion district it is found that the 

 Duluth gabbro is in contact with the 'series on its southern side. It is 

 veiy noticeable, also, that in all cases where the Gunflint beds are in con- 

 tact with this gabbro the rocks have been extremely metamorphosed. This 

 metamorjDhism is most noticeable immediately at the contact, diminishing 

 in extent as the distance away from this contact increases. These facts 



«The Mesabi iron-bearing district of Minnesota, by C. K. Leith: Mon. U. S. Geol. Survey Vol. 

 XLIII, 1903, p. 180. 



