234 THE MARQUETTE IliOX-BEAlilNG DISTI.'K'T. 



(loulit that tlie slate is the noncougloiueratie phase of tlie formation. 

 This shite, l)v l)e('oniiiig more and more (juartzose, j)asses into vitreous 

 quartzite, whicli sliows hirge exposures just north of Mud Lake. This 

 more resistant rook seems to have heen upturned without liaviug- received 

 tlie minor plications which are found in the slate. The soft slate was 

 hetweeu the heavy beds of quartzite on the one side and the strong Mona 

 schists on the other; and doubtless the larger part of the readjustment 

 Avhich was necessary when the layers were folded together took jilace in the 

 slates, and are thus explained the profound d^'namic effects there seen. 



An examination of the conglomerates and slates in thin section fully 

 confirms all that has lieen said in reference to the relations of the rocks as 

 seen in the ficdd. The predominant pebbles from the State road con- 

 glomerate conqirisc ;dinost everv phase of the peculiar rocks of the Mona- 

 scliist formation in the neighborhood of Marquette. There are also 

 found abundantly coarse-grained granite, the peculiar red granite, and a 

 finer-grained, felilsj)atlii('-looking granite, all of which in dikes cut the Mona 

 schists. The matrix of the conglomerate is of the ground-up detritus of the 

 same material, feldspar however being jiredominant, because of the basic 

 character of the rocks from which the material is derived. In thin section 

 a few chert fragments were found. These A^ere not in the form yf pebbles, 

 but this occurrence microscopically connects this conglomerate with the 

 conglomerate which occurs on ]\Iount ( )mimi. It has been stated tliat 

 probably the conglomerate grades u]) into the slates and graywackes on 

 the south side of the road. The latter jirove in thin section to be identical 

 in character with the matrix of the conglomerate. The quartzites are found 

 to be typical of the formation, and need no descri])tion. 



Mount omimi. — ( )u the stcep uorthem slope of Mount ( )mimi (Atlas Slieets 

 XXXVI and XXXVI II), in the northern jiart of sees. 33 and 34, T. 48 N., R. 

 25 W., occurs a conglomerate, varying from 10 to 40 feet in thickness. This 

 conglomerate has a ferruginous gray wacke background, and contains numer- 

 ous pebbles of banded, cherty-lookiug (juartz, of white crystalline quartz, 

 of ferruginous chert and jasper, of heavily ferruginous pebbles, of white 

 schistose graywacke, and of green schi.st. It is underlain by coarse gray- 

 wacke and slate, and is overlain by slates and graywackes, interstratified 



