THE LOWER HURONIAN. 349 



strongly that it is onl}^ after very close study that they can be 

 discriminated. 



At the southwest end of the lake, whose tip just extends into the NE. 

 4 of sec. 11, T. 64 N., R. 8 W., there is a dike of granite-porphyry which 

 cuts across the bedding. Other granite dikes must occur throughout this 

 district cutting these slates, although few of them have been found. One, 

 for instance, occurs upon the south side of the large island in Knife Lake 

 north of sec. 31, T. 65 N., R. 8 W. 



Contact metatnorphism of the slates. — An excellent place at which to see 

 the character of the metamorphosed Knife Lake slates is along the Duluth 

 and Iron Range Railroad, near milepost 92. This place is also very easily 

 reached. 



In going south from Tower after passing the south side of the Ely 

 greenstone one observes the following series of sediments: 



On the first exposure south of the greenstone we get slates and gray- 

 wackes, which are, even in this first exposure, somewhat metamorphosed — 

 that is, they are very firm slates and quite thoroxighly indurated graywackes, 

 but still show very clearly their unmistakable sedimentary characters. The 

 first granite dikes observed in these sediments occur about a mile south of 

 their most northern outcrop. Continuing south from the first outcrops of 

 the sediments on the railroad, the ones to which we come thereafter take 

 on a more and more altei'ed character as we go farther south. At milepost 

 92 the presence of good conglomerates with accompanying finer sediments 

 showing well-marked sedimentary structures such as normal and current bed- 

 ding, indicates with absolute clearness the mode of origin of the rocks. The 

 microscopic study of these rocks is not so satisfactory as the macroscopic; 

 the changes which the rocks have uudei'gone have obliterated all features 

 which would enable one to determine with absolute accuracy by means of 

 the microscope the original characters of these rocks, although the coarse 

 macroscopic structures still remain. Farther south the outcrops become 

 scarcer as we approach the great muskeg area in the low ground north of 

 the Giants range. Nevertheless here the few outcrops which were observed 

 are exceedingly indurated banded rocks which can be more properly spoken 

 of as mica-schists than as graywackes. Still farther south the rocks are 

 mica-schists and mica-gneisses, with very much contorted banding, and 

 are cut by granite dikes. The change in the character of the rocks as 



