THE LOWER HURONIAN. 363 



RELATIONS TO ADJACENT FORMATIONS. 



Relations to the Lotver Huronian. — The Snowbank granite is foimd in 

 contact with the adjacent Lower Huronian sediments, both the Ogishke con- 

 glomerates and the Knife Lake slates. In a number of places dikes, oifshoots 

 from this mass, occur in the adjacent sediments. Moreover, the sediments 

 near the granite have been very much changed. They are full of mica in 

 relatively large crystals, and in general the rocks have been recrystallized 

 until they are now in places mica-schists. The crystalline character of 

 these rocks is most noticeable near their contact with the main granite mass 

 and at places where they are cut through by numerous dikes of the 

 granite and where the fragments of the sediments are 'inclosed in the dike 

 rocks. The farther away from this contact we go the less numerous the 

 dikes become and the less pronounced are the indications of metamorphism 

 until, at a distance varying in places from half a mile to a mile, the 

 sediments seem to show their normal character. The presence of the dikes 

 in the sediments and the contact effect of the granite on the sediments 

 clearly show the intrusive character of the granite. The facts referred to 

 briefly above were observed and recorded in their notebooks by the 

 members of the Minnesota survey, but the interpretation given to these 

 facts by the State geologist is very different from that given above. 

 According to him the Snowbank granite is a product of the metamorphism 

 of acid sediments, graywackes, and conglomerates, and the granite and 

 granite-porphyries are connecting linlvs showing transitions to the sedi- 

 ments. The complete fusion of these graywackes produced the granite. 

 Incomplete fusion accounts for the metamorphosed sediments surrounding 

 the granite massive. The dikes in the sediments at some distance from the 

 border of the granite are portions of the molten sediments which penetrated 

 the unfused ones. 



Relations to the Keiveenaivan gabhro. — The granite has not been found 

 in actual contact with the large mass of Duluth gabbro lying south of 

 and next to it. Along the contact there is a slight topographic break, 

 occupied by low ground, in which exposures are wanting. The granite 

 is of Lower Huronian age, and there can be no doubt that the Duluth 

 gabbro is younger than it is. However, if the gabbro exercised any 



"Geol. and Nat. Hist. Survey of Mitmesota, Final Rept., Vol. IV, 1899, pp. 287-294. 



